Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753649Ab1FBTmh (ORCPT ); Thu, 2 Jun 2011 15:42:37 -0400 Received: from e9.ny.us.ibm.com ([32.97.182.139]:60320 "EHLO e9.ny.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752465Ab1FBTmg (ORCPT ); Thu, 2 Jun 2011 15:42:36 -0400 Date: Thu, 2 Jun 2011 12:42:31 -0700 From: "Paul E. McKenney" To: Will Drewry Cc: linux-kernel@vger.kernel.org, kees.cook@canonical.com, torvalds@linux-foundation.org, tglx@linutronix.de, mingo@elte.hu, rostedt@goodmis.org, jmorris@namei.org, Peter Zijlstra , Frederic Weisbecker , linux-security-module@vger.kernel.org Subject: Re: [PATCH v3 03/13] seccomp_filters: new mode with configurable syscall filters Message-ID: <20110602194231.GL2271@linux.vnet.ibm.com> Reply-To: paulmck@linux.vnet.ibm.com References: <1306897845-9393-3-git-send-email-wad@chromium.org> <20110602173654.GI2271@linux.vnet.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: User-Agent: Mutt/1.5.20 (2009-06-14) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 50698 Lines: 1368 On Thu, Jun 02, 2011 at 01:14:54PM -0500, Will Drewry wrote: > On Thu, Jun 2, 2011 at 12:36 PM, Paul E. McKenney > wrote: > > On Tue, May 31, 2011 at 10:10:35PM -0500, Will Drewry wrote: > >> This change adds a new seccomp mode which specifies the allowed system > >> calls dynamically. ?When in the new mode (2), all system calls are > >> checked against process-defined filters - first by system call number, > >> then by a filter string. ?If an entry exists for a given system call and > >> all filter predicates evaluate to true, then the task may proceed. > >> Otherwise, the task is killed. > > > > A few questions below -- I can't say that I understand the RCU usage. > > > > ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ?Thanx, Paul > > > >> Filter string parsing and evaluation is handled by the ftrace filter > >> engine. ?Related patches tweak to the perf filter trace and free > >> allowing the calls to be shared. Filters inherit their understanding of > >> types and arguments for each system call from the CONFIG_FTRACE_SYSCALLS > >> subsystem which already populates this information in syscall_metadata > >> associated enter_event (and exit_event) structures. If > >> CONFIG_FTRACE_SYSCALLS is not compiled in, only filter strings of "1" > >> will be allowed. > >> > >> The net result is a process may have its system calls filtered using the > >> ftrace filter engine's inherent understanding of systems calls. ?The set > >> of filters is specified through the PR_SET_SECCOMP_FILTER argument in > >> prctl(). For example, a filterset for a process, like pdftotext, that > >> should only process read-only input could (roughly) look like: > >> ? sprintf(rdonly, "flags == %u", O_RDONLY|O_LARGEFILE); > >> ? prctl(PR_SET_SECCOMP_FILTER, __NR_open, rdonly); > >> ? prctl(PR_SET_SECCOMP_FILTER, __NR__llseek, "1"); > >> ? prctl(PR_SET_SECCOMP_FILTER, __NR_brk, "1"); > >> ? prctl(PR_SET_SECCOMP_FILTER, __NR_close, "1"); > >> ? prctl(PR_SET_SECCOMP_FILTER, __NR_exit_group, "1"); > >> ? prctl(PR_SET_SECCOMP_FILTER, __NR_fstat64, "1"); > >> ? prctl(PR_SET_SECCOMP_FILTER, __NR_mmap2, "1"); > >> ? prctl(PR_SET_SECCOMP_FILTER, __NR_munmap, "1"); > >> ? prctl(PR_SET_SECCOMP_FILTER, __NR_read, "1"); > >> ? prctl(PR_SET_SECCOMP_FILTER, __NR_write, "(fd == 1 | fd == 2)"); > >> ? prctl(PR_SET_SECCOMP, 2); > >> > >> Subsequent calls to PR_SET_SECCOMP_FILTER for the same system call will > >> be &&'d together to ensure that attack surface may only be reduced: > >> ? prctl(PR_SET_SECCOMP_FILTER, __NR_write, "fd != 2"); > >> > >> With the earlier example, the active filter becomes: > >> ? "(fd == 1 || fd == 2) && fd != 2" > >> > >> The patch also adds PR_CLEAR_SECCOMP_FILTER and PR_GET_SECCOMP_FILTER. > >> The latter returns the current filter for a system call to userspace: > >> > >> ? prctl(PR_GET_SECCOMP_FILTER, __NR_write, buf, bufsize); > >> > >> while the former clears any filters for a given system call changing it > >> back to a defaulty deny: > >> > >> ? prctl(PR_CLEAR_SECCOMP_FILTER, __NR_write); > >> > >> v3: - always block execve calls (as per linus torvalds) > >> ? ? - add __NR_seccomp_execve(_32) to seccomp-supporting arches > >> ? ? - ensure compat tasks can't reach ftrace:syscalls > >> ? ? - dropped new defines for seccomp modes. > >> ? ? - two level array instead of hlists (sugg. by olof johansson) > >> ? ? - added generic Kconfig entry that is not connected. > >> ? ? - dropped internal seccomp.h > >> ? ? - move prctl helpers to seccomp_filter > >> ? ? - killed seccomp_t typedef (as per checkpatch) > >> v2: - changed to use the existing syscall number ABI. > >> ? ? - prctl changes to minimize parsing in the kernel: > >> ? ? ? prctl(PR_SET_SECCOMP, {0 | 1 | 2 }, { 0 | ON_EXEC }); > >> ? ? ? prctl(PR_SET_SECCOMP_FILTER, __NR_read, "fd == 5"); > >> ? ? ? prctl(PR_CLEAR_SECCOMP_FILTER, __NR_read); > >> ? ? ? prctl(PR_GET_SECCOMP_FILTER, __NR_read, buf, bufsize); > >> ? ? - defined PR_SECCOMP_MODE_STRICT and ..._FILTER > >> ? ? - added flags > >> ? ? - provide a default fail syscall_nr_to_meta in ftrace > >> ? ? - provides fallback for unhooked system calls > >> ? ? - use -ENOSYS and ERR_PTR(-ENOSYS) for stubbed functionality > >> ? ? - added kernel/seccomp.h to share seccomp.c/seccomp_filter.c > >> ? ? - moved to a hlist and 4 bit hash of linked lists > >> ? ? - added support to operate without CONFIG_FTRACE_SYSCALLS > >> ? ? - moved Kconfig support next to SECCOMP > >> ? ? - made Kconfig entries dependent on EXPERIMENTAL > >> ? ? - added macros to avoid ifdefs from kernel/fork.c > >> ? ? - added compat task/filter matching > >> ? ? - drop seccomp.h inclusion in sched.h and drop seccomp_t > >> ? ? - added Filtering to "show" output > >> ? ? - added on_exec state dup'ing when enabling after a fast-path accept. > >> > >> Signed-off-by: Will Drewry > >> --- > >> ?include/linux/prctl.h ? | ? ?5 + > >> ?include/linux/sched.h ? | ? ?2 +- > >> ?include/linux/seccomp.h | ? 98 ++++++- > >> ?include/trace/syscall.h | ? ?7 + > >> ?kernel/Makefile ? ? ? ? | ? ?3 + > >> ?kernel/fork.c ? ? ? ? ? | ? ?3 + > >> ?kernel/seccomp.c ? ? ? ?| ? 38 ++- > >> ?kernel/seccomp_filter.c | ?784 +++++++++++++++++++++++++++++++++++++++++++++++ > >> ?kernel/sys.c ? ? ? ? ? ?| ? 13 +- > >> ?security/Kconfig ? ? ? ?| ? 17 + > >> ?10 files changed, 954 insertions(+), 16 deletions(-) > >> ?create mode 100644 kernel/seccomp_filter.c > >> > >> diff --git a/include/linux/prctl.h b/include/linux/prctl.h > >> index a3baeb2..44723ce 100644 > >> --- a/include/linux/prctl.h > >> +++ b/include/linux/prctl.h > >> @@ -64,6 +64,11 @@ > >> ?#define PR_GET_SECCOMP ? ? ? 21 > >> ?#define PR_SET_SECCOMP ? ? ? 22 > >> > >> +/* Get/set process seccomp filters */ > >> +#define PR_GET_SECCOMP_FILTER ? ? ? ?35 > >> +#define PR_SET_SECCOMP_FILTER ? ? ? ?36 > >> +#define PR_CLEAR_SECCOMP_FILTER ? ? ?37 > >> + > >> ?/* Get/set the capability bounding set (as per security/commoncap.c) */ > >> ?#define PR_CAPBSET_READ 23 > >> ?#define PR_CAPBSET_DROP 24 > >> diff --git a/include/linux/sched.h b/include/linux/sched.h > >> index 18d63ce..3f0bc8d 100644 > >> --- a/include/linux/sched.h > >> +++ b/include/linux/sched.h > >> @@ -1374,7 +1374,7 @@ struct task_struct { > >> ? ? ? uid_t loginuid; > >> ? ? ? unsigned int sessionid; > >> ?#endif > >> - ? ? seccomp_t seccomp; > >> + ? ? struct seccomp_struct seccomp; > >> > >> ?/* Thread group tracking */ > >> ? ? ? u32 parent_exec_id; > >> diff --git a/include/linux/seccomp.h b/include/linux/seccomp.h > >> index 167c333..f4434ca 100644 > >> --- a/include/linux/seccomp.h > >> +++ b/include/linux/seccomp.h > >> @@ -1,13 +1,33 @@ > >> ?#ifndef _LINUX_SECCOMP_H > >> ?#define _LINUX_SECCOMP_H > >> > >> +struct seq_file; > >> > >> ?#ifdef CONFIG_SECCOMP > >> > >> +#include > >> ?#include > >> +#include > >> ?#include > >> > >> -typedef struct { int mode; } seccomp_t; > >> +struct seccomp_filters; > >> +/** > >> + * struct seccomp_struct - the state of a seccomp'ed process > >> + * > >> + * @mode: > >> + * ? ? if this is 1, the process is under standard seccomp rules > >> + * ? ? ? ? ? ? is 2, the process is only allowed to make system calls where > >> + * ? ? ? ? ? ? ? ? ? associated filters evaluate successfully. > >> + * @filters: Metadata for filters if using CONFIG_SECCOMP_FILTER. > >> + * ? ? ? ? ? filters assignment/use should be RCU-protected and its contents > >> + * ? ? ? ? ? should never be modified when attached to a seccomp_struct. > >> + */ > >> +struct seccomp_struct { > >> + ? ? uint16_t mode; > >> +#ifdef CONFIG_SECCOMP_FILTER > >> + ? ? struct seccomp_filters *filters; > >> +#endif > >> +}; > >> > >> ?extern void __secure_computing(int); > >> ?static inline void secure_computing(int this_syscall) > >> @@ -16,15 +36,14 @@ static inline void secure_computing(int this_syscall) > >> ? ? ? ? ? ? ? __secure_computing(this_syscall); > >> ?} > >> > >> -extern long prctl_get_seccomp(void); > >> ?extern long prctl_set_seccomp(unsigned long); > >> +extern long prctl_get_seccomp(void); > >> > >> ?#else /* CONFIG_SECCOMP */ > >> > >> ?#include > >> > >> -typedef struct { } seccomp_t; > >> - > >> +struct seccomp_struct { }; > >> ?#define secure_computing(x) do { } while (0) > >> > >> ?static inline long prctl_get_seccomp(void) > >> @@ -32,11 +51,80 @@ static inline long prctl_get_seccomp(void) > >> ? ? ? return -EINVAL; > >> ?} > >> > >> -static inline long prctl_set_seccomp(unsigned long arg2) > >> +static inline long prctl_set_seccomp(unsigned long a2); > >> ?{ > >> ? ? ? return -EINVAL; > >> ?} > >> > >> ?#endif /* CONFIG_SECCOMP */ > >> > >> +#ifdef CONFIG_SECCOMP_FILTER > >> + > >> +#define inherit_tsk_seccomp(_child, _orig) do { \ > >> + ? ? _child->seccomp.mode = _orig->seccomp.mode; \ > >> + ? ? _child->seccomp.filters = get_seccomp_filters(_orig->seccomp.filters); \ > >> + ? ? } while (0) > >> +#define put_tsk_seccomp(_tsk) put_seccomp_filters(_tsk->seccomp.filters) > >> + > >> +extern int seccomp_show_filters(struct seccomp_filters *filters, > >> + ? ? ? ? ? ? ? ? ? ? ? ? ? ? struct seq_file *); > >> +extern long seccomp_set_filter(int, char *); > >> +extern long seccomp_clear_filter(int); > >> +extern long seccomp_get_filter(int, char *, unsigned long); > >> + > >> +extern long prctl_set_seccomp_filter(unsigned long, char __user *); > >> +extern long prctl_get_seccomp_filter(unsigned long, char __user *, > >> + ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ?unsigned long); > >> +extern long prctl_clear_seccomp_filter(unsigned long); > >> + > >> +extern struct seccomp_filters *get_seccomp_filters(struct seccomp_filters *); > >> +extern void put_seccomp_filters(struct seccomp_filters *); > >> + > >> +extern int seccomp_test_filters(int); > >> +extern void seccomp_filter_log_failure(int); > >> + > >> +#else ?/* CONFIG_SECCOMP_FILTER */ > >> + > >> +struct seccomp_filters { }; > >> +#define inherit_tsk_seccomp(_child, _orig) do { } while (0) > >> +#define put_tsk_seccomp(_tsk) do { } while (0) > >> + > >> +static inline int seccomp_show_filters(struct seccomp_filters *filters, > >> + ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ?struct seq_file *m) > >> +{ > >> + ? ? return -ENOSYS; > >> +} > >> + > >> +static inline long seccomp_set_filter(int syscall_nr, char *filter) > >> +{ > >> + ? ? return -ENOSYS; > >> +} > >> + > >> +static inline long seccomp_clear_filter(int syscall_nr) > >> +{ > >> + ? ? return -ENOSYS; > >> +} > >> + > >> +static inline long seccomp_get_filter(int syscall_nr, > >> + ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? char *buf, unsigned long available) > >> +{ > >> + ? ? return -ENOSYS; > >> +} > >> + > >> +static inline long prctl_set_seccomp_filter(unsigned long a2, char __user *a3) > >> +{ > >> + ? ? return -ENOSYS; > >> +} > >> + > >> +static inline long prctl_clear_seccomp_filter(unsigned long a2) > >> +{ > >> + ? ? return -ENOSYS; > >> +} > >> + > >> +static inline long prctl_get_seccomp_filter(unsigned long a2, char __user *a3, > >> + ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? unsigned long a4) > >> +{ > >> + ? ? return -ENOSYS; > >> +} > >> +#endif ?/* CONFIG_SECCOMP_FILTER */ > >> ?#endif /* _LINUX_SECCOMP_H */ > >> diff --git a/include/trace/syscall.h b/include/trace/syscall.h > >> index 242ae04..e061ad0 100644 > >> --- a/include/trace/syscall.h > >> +++ b/include/trace/syscall.h > >> @@ -35,6 +35,8 @@ struct syscall_metadata { > >> ?extern unsigned long arch_syscall_addr(int nr); > >> ?extern int init_syscall_trace(struct ftrace_event_call *call); > >> > >> +extern struct syscall_metadata *syscall_nr_to_meta(int); > >> + > >> ?extern int reg_event_syscall_enter(struct ftrace_event_call *call); > >> ?extern void unreg_event_syscall_enter(struct ftrace_event_call *call); > >> ?extern int reg_event_syscall_exit(struct ftrace_event_call *call); > >> @@ -49,6 +51,11 @@ enum print_line_t print_syscall_enter(struct trace_iterator *iter, int flags, > >> ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? struct trace_event *event); > >> ?enum print_line_t print_syscall_exit(struct trace_iterator *iter, int flags, > >> ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ?struct trace_event *event); > >> +#else > >> +static inline struct syscall_metadata *syscall_nr_to_meta(int nr) > >> +{ > >> + ? ? return NULL; > >> +} > >> ?#endif > >> > >> ?#ifdef CONFIG_PERF_EVENTS > >> diff --git a/kernel/Makefile b/kernel/Makefile > >> index 85cbfb3..84e7dfb 100644 > >> --- a/kernel/Makefile > >> +++ b/kernel/Makefile > >> @@ -81,6 +81,9 @@ obj-$(CONFIG_DETECT_HUNG_TASK) += hung_task.o > >> ?obj-$(CONFIG_LOCKUP_DETECTOR) += watchdog.o > >> ?obj-$(CONFIG_GENERIC_HARDIRQS) += irq/ > >> ?obj-$(CONFIG_SECCOMP) += seccomp.o > >> +ifeq ($(CONFIG_SECCOMP_FILTER),y) > >> +obj-$(CONFIG_SECCOMP) += seccomp_filter.o > >> +endif > >> ?obj-$(CONFIG_RCU_TORTURE_TEST) += rcutorture.o > >> ?obj-$(CONFIG_TREE_RCU) += rcutree.o > >> ?obj-$(CONFIG_TREE_PREEMPT_RCU) += rcutree.o > >> diff --git a/kernel/fork.c b/kernel/fork.c > >> index e7548de..6f835e0 100644 > >> --- a/kernel/fork.c > >> +++ b/kernel/fork.c > >> @@ -34,6 +34,7 @@ > >> ?#include > >> ?#include > >> ?#include > >> +#include > >> ?#include > >> ?#include > >> ?#include > >> @@ -169,6 +170,7 @@ void free_task(struct task_struct *tsk) > >> ? ? ? free_thread_info(tsk->stack); > >> ? ? ? rt_mutex_debug_task_free(tsk); > >> ? ? ? ftrace_graph_exit_task(tsk); > >> + ? ? put_tsk_seccomp(tsk); > >> ? ? ? free_task_struct(tsk); > >> ?} > >> ?EXPORT_SYMBOL(free_task); > >> @@ -280,6 +282,7 @@ static struct task_struct *dup_task_struct(struct task_struct *orig) > >> ? ? ? if (err) > >> ? ? ? ? ? ? ? goto out; > >> > >> + ? ? inherit_tsk_seccomp(tsk, orig); > >> ? ? ? setup_thread_stack(tsk, orig); > >> ? ? ? clear_user_return_notifier(tsk); > >> ? ? ? clear_tsk_need_resched(tsk); > >> diff --git a/kernel/seccomp.c b/kernel/seccomp.c > >> index 57d4b13..0a942be 100644 > >> --- a/kernel/seccomp.c > >> +++ b/kernel/seccomp.c > >> @@ -2,16 +2,20 @@ > >> ? * linux/kernel/seccomp.c > >> ? * > >> ? * Copyright 2004-2005 ?Andrea Arcangeli > >> + * Copyright (C) 2011 The Chromium OS Authors > >> ? * > >> ? * This defines a simple but solid secure-computing mode. > >> ? */ > >> > >> ?#include > >> ?#include > >> +#include > >> ?#include > >> +#include > >> +#include > >> > >> +#define SECCOMP_MAX_FILTER_LENGTH MAX_FILTER_STR_VAL > >> ?/* #define SECCOMP_DEBUG 1 */ > >> -#define NR_SECCOMP_MODES 1 > >> > >> ?/* > >> ? * Secure computing mode 1 allows only read/write/exit/sigreturn. > >> @@ -32,10 +36,9 @@ static int mode1_syscalls_32[] = { > >> > >> ?void __secure_computing(int this_syscall) > >> ?{ > >> - ? ? int mode = current->seccomp.mode; > >> ? ? ? int * syscall; > >> > >> - ? ? switch (mode) { > >> + ? ? switch (current->seccomp.mode) { > >> ? ? ? case 1: > >> ? ? ? ? ? ? ? syscall = mode1_syscalls; > >> ?#ifdef CONFIG_COMPAT > >> @@ -47,6 +50,17 @@ void __secure_computing(int this_syscall) > >> ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? return; > >> ? ? ? ? ? ? ? } while (*++syscall); > >> ? ? ? ? ? ? ? break; > >> +#ifdef CONFIG_SECCOMP_FILTER > >> + ? ? case 2: > >> + ? ? ? ? ? ? if (this_syscall >= NR_syscalls || this_syscall < 0) > >> + ? ? ? ? ? ? ? ? ? ? break; > >> + > >> + ? ? ? ? ? ? if (!seccomp_test_filters(this_syscall)) > >> + ? ? ? ? ? ? ? ? ? ? return; > >> + > >> + ? ? ? ? ? ? seccomp_filter_log_failure(this_syscall); > >> + ? ? ? ? ? ? break; > >> +#endif > >> ? ? ? default: > >> ? ? ? ? ? ? ? BUG(); > >> ? ? ? } > >> @@ -71,16 +85,22 @@ long prctl_set_seccomp(unsigned long seccomp_mode) > >> ? ? ? if (unlikely(current->seccomp.mode)) > >> ? ? ? ? ? ? ? goto out; > >> > >> - ? ? ret = -EINVAL; > >> - ? ? if (seccomp_mode && seccomp_mode <= NR_SECCOMP_MODES) { > >> - ? ? ? ? ? ? current->seccomp.mode = seccomp_mode; > >> - ? ? ? ? ? ? set_thread_flag(TIF_SECCOMP); > >> + ? ? ret = 0; > >> + ? ? switch (seccomp_mode) { > >> + ? ? case 1: > >> ?#ifdef TIF_NOTSC > >> ? ? ? ? ? ? ? disable_TSC(); > >> ?#endif > >> - ? ? ? ? ? ? ret = 0; > >> +#ifdef CONFIG_SECCOMP_FILTER > >> + ? ? case 2: > >> +#endif > >> + ? ? ? ? ? ? current->seccomp.mode = seccomp_mode; > >> + ? ? ? ? ? ? set_thread_flag(TIF_SECCOMP); > >> + ? ? ? ? ? ? break; > >> + ? ? default: > >> + ? ? ? ? ? ? ret = -EINVAL; > >> ? ? ? } > >> > >> - out: > >> +out: > >> ? ? ? return ret; > >> ?} > >> diff --git a/kernel/seccomp_filter.c b/kernel/seccomp_filter.c > >> new file mode 100644 > >> index 0000000..9782f25 > >> --- /dev/null > >> +++ b/kernel/seccomp_filter.c > >> @@ -0,0 +1,784 @@ > >> +/* filter engine-based seccomp system call filtering > >> + * > >> + * This program is free software; you can redistribute it and/or modify > >> + * it under the terms of the GNU General Public License as published by > >> + * the Free Software Foundation; either version 2 of the License, or > >> + * (at your option) any later version. > >> + * > >> + * This program is distributed in the hope that it will be useful, > >> + * but WITHOUT ANY WARRANTY; without even the implied warranty of > >> + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. ?See the > >> + * GNU General Public License for more details. > >> + * > >> + * You should have received a copy of the GNU General Public License > >> + * along with this program; if not, write to the Free Software > >> + * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA. > >> + * > >> + * Copyright (C) 2011 The Chromium OS Authors > >> + */ > >> + > >> +#include > >> +#include > >> +#include > >> +#include > >> +#include > >> +#include > >> +#include > >> +#include > >> +#include > >> + > >> +#include > >> +#include > >> + > >> + > >> +#define SECCOMP_MAX_FILTER_LENGTH MAX_FILTER_STR_VAL > >> + > >> +#define SECCOMP_FILTER_ALLOW "1" > >> +#define SECCOMP_ACTION_DENY 0xffff > >> +#define SECCOMP_ACTION_ALLOW 0xfffe > >> + > >> +/** > >> + * struct seccomp_filters - container for seccomp filterset > >> + * > >> + * @syscalls: array of 16-bit indices into @event_filters by syscall_nr > >> + * ? ? ? ? ? ?May also be SECCOMP_ACTION_DENY or SECCOMP_ACTION_ALLOW > >> + * @event_filters: array of pointers to ftrace event objects > >> + * @count: size of @event_filters > >> + * @flags: anonymous struct to wrap filters-specific flags > >> + * @usage: reference count to simplify use. > >> + */ > >> +struct seccomp_filters { > >> + ? ? uint16_t syscalls[NR_syscalls]; > >> + ? ? struct event_filter **event_filters; > >> + ? ? uint16_t count; > >> + ? ? struct { > >> + ? ? ? ? ? ? uint32_t compat:1, > >> + ? ? ? ? ? ? ? ? ? ? ?__reserved:31; > >> + ? ? } flags; > >> + ? ? atomic_t usage; > >> +}; > >> + > >> +/* Handle ftrace symbol non-existence */ > >> +#ifdef CONFIG_FTRACE_SYSCALLS > >> +#define create_event_filter(_ef_pptr, _event_type, _str) \ > >> + ? ? ftrace_parse_filter(_ef_pptr, _event_type, _str) > >> +#define get_filter_string(_ef) ftrace_get_filter_string(_ef) > >> +#define free_event_filter(_f) ftrace_free_filter(_f) > >> + > >> +#else > >> + > >> +#define create_event_filter(_ef_pptr, _event_type, _str) (-ENOSYS) > >> +#define get_filter_string(_ef) (NULL) > >> +#define free_event_filter(_f) do { } while (0) > >> +#endif > >> + > >> +/** > >> + * seccomp_filters_new - allocates a new filters object > >> + * @count: count to allocate for the event_filters array > >> + * > >> + * Returns ERR_PTR on error or an allocated object. > >> + */ > >> +static struct seccomp_filters *seccomp_filters_new(uint16_t count) > >> +{ > >> + ? ? struct seccomp_filters *f; > >> + > >> + ? ? if (count >= SECCOMP_ACTION_ALLOW) > >> + ? ? ? ? ? ? return ERR_PTR(-EINVAL); > >> + > >> + ? ? f = kzalloc(sizeof(struct seccomp_filters), GFP_KERNEL); > >> + ? ? if (!f) > >> + ? ? ? ? ? ? return ERR_PTR(-ENOMEM); > >> + > >> + ? ? /* Lazy SECCOMP_ACTION_DENY assignment. */ > >> + ? ? memset(f->syscalls, 0xff, sizeof(f->syscalls)); > >> + ? ? atomic_set(&f->usage, 1); > >> + > >> + ? ? f->event_filters = NULL; > >> + ? ? f->count = count; > >> + ? ? if (!count) > >> + ? ? ? ? ? ? return f; > >> + > >> + ? ? f->event_filters = kzalloc(count * sizeof(struct event_filter *), > >> + ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ?GFP_KERNEL); > >> + ? ? if (!f->event_filters) { > >> + ? ? ? ? ? ? kfree(f); > >> + ? ? ? ? ? ? f = ERR_PTR(-ENOMEM); > >> + ? ? } > >> + ? ? return f; > >> +} > >> + > >> +/** > >> + * seccomp_filters_free - cleans up the filter list and frees the table > >> + * @filters: NULL or live object to be completely destructed. > >> + */ > >> +static void seccomp_filters_free(struct seccomp_filters *filters) > >> +{ > >> + ? ? uint16_t count = 0; > >> + ? ? if (!filters) > >> + ? ? ? ? ? ? return; > >> + ? ? while (count < filters->count) { > >> + ? ? ? ? ? ? struct event_filter *f = filters->event_filters[count]; > >> + ? ? ? ? ? ? free_event_filter(f); > >> + ? ? ? ? ? ? count++; > >> + ? ? } > >> + ? ? kfree(filters->event_filters); > >> + ? ? kfree(filters); > >> +} > >> + > >> +static void __put_seccomp_filters(struct seccomp_filters *orig) > >> +{ > >> + ? ? WARN_ON(atomic_read(&orig->usage)); > >> + ? ? seccomp_filters_free(orig); > >> +} > >> + > >> +#define seccomp_filter_allow(_id) ((_id) == SECCOMP_ACTION_ALLOW) > >> +#define seccomp_filter_deny(_id) ((_id) == SECCOMP_ACTION_DENY) > >> +#define seccomp_filter_dynamic(_id) \ > >> + ? ? (!seccomp_filter_allow(_id) && !seccomp_filter_deny(_id)) > >> +static inline uint16_t seccomp_filter_id(const struct seccomp_filters *f, > >> + ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ?int syscall_nr) > >> +{ > >> + ? ? if (!f) > >> + ? ? ? ? ? ? return SECCOMP_ACTION_DENY; > >> + ? ? return f->syscalls[syscall_nr]; > >> +} > >> + > >> +static inline struct event_filter *seccomp_dynamic_filter( > >> + ? ? ? ? ? ? const struct seccomp_filters *filters, uint16_t id) > >> +{ > >> + ? ? if (!seccomp_filter_dynamic(id)) > >> + ? ? ? ? ? ? return NULL; > >> + ? ? return filters->event_filters[id]; > >> +} > >> + > >> +static inline void set_seccomp_filter_id(struct seccomp_filters *filters, > >> + ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ?int syscall_nr, uint16_t id) > >> +{ > >> + ? ? filters->syscalls[syscall_nr] = id; > >> +} > >> + > >> +static inline void set_seccomp_filter(struct seccomp_filters *filters, > >> + ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? int syscall_nr, uint16_t id, > >> + ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? struct event_filter *dynamic_filter) > >> +{ > >> + ? ? filters->syscalls[syscall_nr] = id; > >> + ? ? if (seccomp_filter_dynamic(id)) > >> + ? ? ? ? ? ? filters->event_filters[id] = dynamic_filter; > >> +} > >> + > >> +static struct event_filter *alloc_event_filter(int syscall_nr, > >> + ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ?const char *filter_string) > >> +{ > >> + ? ? struct syscall_metadata *data; > >> + ? ? struct event_filter *filter = NULL; > >> + ? ? int err; > >> + > >> + ? ? data = syscall_nr_to_meta(syscall_nr); > >> + ? ? /* Argument-based filtering only works on ftrace-hooked syscalls. */ > >> + ? ? err = -ENOSYS; > >> + ? ? if (!data) > >> + ? ? ? ? ? ? goto fail; > >> + ? ? err = create_event_filter(&filter, > >> + ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? data->enter_event->event.type, > >> + ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? filter_string); > >> + ? ? if (err) > >> + ? ? ? ? ? ? goto fail; > >> + > >> + ? ? return filter; > >> +fail: > >> + ? ? kfree(filter); > >> + ? ? return ERR_PTR(err); > >> +} > >> + > >> +/** > >> + * seccomp_filters_copy - copies filters from src to dst. > >> + * > >> + * @dst: seccomp_filters to populate. > >> + * @src: table to read from. > >> + * @skip: specifies an entry, by system call, to skip. > >> + * > >> + * Returns non-zero on failure. > >> + * Both the source and the destination should have no simultaneous > >> + * writers, and dst should be exclusive to the caller. > >> + * If @skip is < 0, it is ignored. > >> + */ > >> +static int seccomp_filters_copy(struct seccomp_filters *dst, > >> + ? ? ? ? ? ? ? ? ? ? ? ? ? ? const struct seccomp_filters *src, > >> + ? ? ? ? ? ? ? ? ? ? ? ? ? ? int skip) > >> +{ > >> + ? ? int id = 0, ret = 0, nr; > >> + ? ? memcpy(&dst->flags, &src->flags, sizeof(src->flags)); > >> + ? ? memcpy(dst->syscalls, src->syscalls, sizeof(dst->syscalls)); > >> + ? ? if (!src->count) > >> + ? ? ? ? ? ? goto done; > >> + ? ? for (nr = 0; nr < NR_syscalls; ++nr) { > >> + ? ? ? ? ? ? struct event_filter *filter; > >> + ? ? ? ? ? ? const char *str; > >> + ? ? ? ? ? ? uint16_t src_id = seccomp_filter_id(src, nr); > >> + ? ? ? ? ? ? if (nr == skip) { > >> + ? ? ? ? ? ? ? ? ? ? set_seccomp_filter(dst, nr, SECCOMP_ACTION_DENY, > >> + ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ?NULL); > >> + ? ? ? ? ? ? ? ? ? ? continue; > >> + ? ? ? ? ? ? } > >> + ? ? ? ? ? ? if (!seccomp_filter_dynamic(src_id)) > >> + ? ? ? ? ? ? ? ? ? ? continue; > >> + ? ? ? ? ? ? if (id >= dst->count) { > >> + ? ? ? ? ? ? ? ? ? ? ret = -EINVAL; > >> + ? ? ? ? ? ? ? ? ? ? goto done; > >> + ? ? ? ? ? ? } > >> + ? ? ? ? ? ? str = get_filter_string(seccomp_dynamic_filter(src, src_id)); > >> + ? ? ? ? ? ? filter = alloc_event_filter(nr, str); > >> + ? ? ? ? ? ? if (IS_ERR(filter)) { > >> + ? ? ? ? ? ? ? ? ? ? ret = PTR_ERR(filter); > >> + ? ? ? ? ? ? ? ? ? ? goto done; > >> + ? ? ? ? ? ? } > >> + ? ? ? ? ? ? set_seccomp_filter(dst, nr, id, filter); > >> + ? ? ? ? ? ? id++; > >> + ? ? } > >> + > >> +done: > >> + ? ? return ret; > >> +} > >> + > >> +/** > >> + * seccomp_extend_filter - appends more text to a syscall_nr's filter > >> + * @filters: unattached filter object to operate on > >> + * @syscall_nr: syscall number to update filters for > >> + * @filter_string: string to append to the existing filter > >> + * > >> + * The new string will be &&'d to the original filter string to ensure that it > >> + * always matches the existing predicates or less: > >> + * ? (old_filter) && @filter_string > >> + * A new seccomp_filters instance is returned on success and a ERR_PTR on > >> + * failure. > >> + */ > >> +static int seccomp_extend_filter(struct seccomp_filters *filters, > >> + ? ? ? ? ? ? ? ? ? ? ? ? ? ? ?int syscall_nr, char *filter_string) > >> +{ > >> + ? ? struct event_filter *filter; > >> + ? ? uint16_t id = seccomp_filter_id(filters, syscall_nr); > >> + ? ? char *merged = NULL; > >> + ? ? int ret = -EINVAL, expected; > >> + > >> + ? ? /* No extending with a "1". */ > >> + ? ? if (!strcmp(SECCOMP_FILTER_ALLOW, filter_string)) > >> + ? ? ? ? ? ? goto out; > >> + > >> + ? ? filter = seccomp_dynamic_filter(filters, id); > >> + ? ? ret = -ENOENT; > >> + ? ? if (!filter) > >> + ? ? ? ? ? ? goto out; > >> + > >> + ? ? merged = kzalloc(SECCOMP_MAX_FILTER_LENGTH + 1, GFP_KERNEL); > >> + ? ? ret = -ENOMEM; > >> + ? ? if (!merged) > >> + ? ? ? ? ? ? goto out; > >> + > >> + ? ? expected = snprintf(merged, SECCOMP_MAX_FILTER_LENGTH, "(%s) && %s", > >> + ? ? ? ? ? ? ? ? ? ? ? ? get_filter_string(filter), filter_string); > >> + ? ? ret = -E2BIG; > >> + ? ? if (expected >= SECCOMP_MAX_FILTER_LENGTH || expected < 0) > >> + ? ? ? ? ? ? goto out; > >> + > >> + ? ? /* Free the old filter */ > >> + ? ? free_event_filter(filter); > >> + ? ? set_seccomp_filter(filters, syscall_nr, id, NULL); > >> + > >> + ? ? /* Replace it */ > >> + ? ? filter = alloc_event_filter(syscall_nr, merged); > >> + ? ? if (IS_ERR(filter)) { > >> + ? ? ? ? ? ? ret = PTR_ERR(filter); > >> + ? ? ? ? ? ? goto out; > >> + ? ? } > >> + ? ? set_seccomp_filter(filters, syscall_nr, id, filter); > >> + ? ? ret = 0; > >> + > >> +out: > >> + ? ? kfree(merged); > >> + ? ? return ret; > >> +} > >> + > >> +/** > >> + * seccomp_add_filter - adds a filter for an unfiltered syscall > >> + * @filters: filters object to add a filter/action to > >> + * @syscall_nr: system call number to add a filter for > >> + * @filter_string: the filter string to apply > >> + * > >> + * Returns 0 on success and non-zero otherwise. > >> + */ > >> +static int seccomp_add_filter(struct seccomp_filters *filters, int syscall_nr, > >> + ? ? ? ? ? ? ? ? ? ? ? ? ? char *filter_string) > >> +{ > >> + ? ? struct event_filter *filter; > >> + ? ? int ret = 0; > >> + > >> + ? ? if (!strcmp(SECCOMP_FILTER_ALLOW, filter_string)) { > >> + ? ? ? ? ? ? set_seccomp_filter(filters, syscall_nr, > >> + ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ?SECCOMP_ACTION_ALLOW, NULL); > >> + ? ? ? ? ? ? goto out; > >> + ? ? } > >> + > >> + ? ? filter = alloc_event_filter(syscall_nr, filter_string); > >> + ? ? if (IS_ERR(filter)) { > >> + ? ? ? ? ? ? ret = PTR_ERR(filter); > >> + ? ? ? ? ? ? goto out; > >> + ? ? } > >> + ? ? /* Always add to the last slot available since additions are > >> + ? ? ?* are only done one at a time. > >> + ? ? ?*/ > >> + ? ? set_seccomp_filter(filters, syscall_nr, filters->count - 1, filter); > >> +out: > >> + ? ? return ret; > >> +} > >> + > >> +/* Wrap optional ftrace syscall support. Returns 1 on match or 0 otherwise. */ > >> +static int filter_match_current(struct event_filter *event_filter) > >> +{ > >> + ? ? int err = 0; > >> +#ifdef CONFIG_FTRACE_SYSCALLS > >> + ? ? uint8_t syscall_state[64]; > >> + > >> + ? ? memset(syscall_state, 0, sizeof(syscall_state)); > >> + > >> + ? ? /* The generic tracing entry can remain zeroed. */ > >> + ? ? err = ftrace_syscall_enter_state(syscall_state, sizeof(syscall_state), > >> + ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ?NULL); > >> + ? ? if (err) > >> + ? ? ? ? ? ? return 0; > >> + > >> + ? ? err = filter_match_preds(event_filter, syscall_state); > >> +#endif > >> + ? ? return err; > >> +} > >> + > >> +static const char *syscall_nr_to_name(int syscall) > >> +{ > >> + ? ? const char *syscall_name = "unknown"; > >> + ? ? struct syscall_metadata *data = syscall_nr_to_meta(syscall); > >> + ? ? if (data) > >> + ? ? ? ? ? ? syscall_name = data->name; > >> + ? ? return syscall_name; > >> +} > >> + > >> +static void filters_set_compat(struct seccomp_filters *filters) > >> +{ > >> +#ifdef CONFIG_COMPAT > >> + ? ? if (is_compat_task()) > >> + ? ? ? ? ? ? filters->flags.compat = 1; > >> +#endif > >> +} > >> + > >> +static inline int filters_compat_mismatch(struct seccomp_filters *filters) > >> +{ > >> + ? ? int ret = 0; > >> + ? ? if (!filters) > >> + ? ? ? ? ? ? return 0; > >> +#ifdef CONFIG_COMPAT > >> + ? ? if (!!(is_compat_task()) == filters->flags.compat) > >> + ? ? ? ? ? ? ret = 1; > >> +#endif > >> + ? ? return ret; > >> +} > >> + > >> +static inline int syscall_is_execve(int syscall) > >> +{ > >> + ? ? int nr = __NR_execve; > >> +#ifdef CONFIG_COMPAT > >> + ? ? if (is_compat_task()) > >> + ? ? ? ? ? ? nr = __NR_seccomp_execve_32; > >> +#endif > >> + ? ? return syscall == nr; > >> +} > >> + > >> +#ifndef KSTK_EIP > >> +#define KSTK_EIP(x) 0L > >> +#endif > >> + > >> +void seccomp_filter_log_failure(int syscall) > >> +{ > >> + ? ? pr_info("%s[%d]: system call %d (%s) blocked at 0x%lx\n", > >> + ? ? ? ? ? ? current->comm, task_pid_nr(current), syscall, > >> + ? ? ? ? ? ? syscall_nr_to_name(syscall), KSTK_EIP(current)); > >> +} > >> + > >> +/* put_seccomp_state - decrements the reference count of @orig and may free. */ > >> +void put_seccomp_filters(struct seccomp_filters *orig) > >> +{ > >> + ? ? if (!orig) > >> + ? ? ? ? ? ? return; > >> + > >> + ? ? if (atomic_dec_and_test(&orig->usage)) > >> + ? ? ? ? ? ? __put_seccomp_filters(orig); > >> +} > >> + > >> +/* get_seccomp_state - increments the reference count of @orig */ > >> +struct seccomp_filters *get_seccomp_filters(struct seccomp_filters *orig) > > > > Nit: the name does not match the comment. > > Will fix it here and above. Thanks! > > >> +{ > >> + ? ? if (!orig) > >> + ? ? ? ? ? ? return NULL; > >> + ? ? atomic_inc(&orig->usage); > >> + ? ? return orig; > > > > This is called in an RCU read-side critical section. ?What exactly is > > RCU protecting? ?I would expect an rcu_dereference() or one of the > > RCU list-traversal primitives somewhere, either here or at the caller. > > Ah, I spaced on rcu_dereference(). The goal was to make the > assignment and replacement of the seccomp_filters pointer > RCU-protected (in seccomp_state) so there's no concern over it being > replaced partial on platforms where pointer assignments are non-atomic > - such as via /proc//seccomp_filters access or a call via the > exported symbols. Object lifetime is managed by reference counting so > that I don't have to worry about extending the RCU read-side critical > section by much or deal with pre-allocations. > > I'll add rcu_dereference() to all the get_seccomp_filters() uses where > it makes sense, so that it is called safely. Just to make sure, does > it make sense to continue to rcu protect the specific pointer? It might. The usual other options is to use a lock outside of the element containing the reference count to protect reference-count manipulation. If there is some convenient lock, especially if it is already held where needed, then locking is more straightforward. Otherwise, RCU is usually a reasonable option. > >> +} > >> + > >> +/** > >> + * seccomp_test_filters - tests 'current' against the given syscall > >> + * @state: seccomp_state of current to use. > >> + * @syscall: number of the system call to test > >> + * > >> + * Returns 0 on ok and non-zero on error/failure. > >> + */ > >> +int seccomp_test_filters(int syscall) > >> +{ > >> + ? ? uint16_t id; > >> + ? ? struct event_filter *filter; > >> + ? ? struct seccomp_filters *filters; > >> + ? ? int ret = -EACCES; > >> + > >> + ? ? rcu_read_lock(); > >> + ? ? filters = get_seccomp_filters(current->seccomp.filters); > >> + ? ? rcu_read_unlock(); > >> + > >> + ? ? if (!filters) > >> + ? ? ? ? ? ? goto out; > >> + > >> + ? ? if (filters_compat_mismatch(filters)) { > >> + ? ? ? ? ? ? pr_info("%s[%d]: seccomp_filter compat() mismatch.\n", > >> + ? ? ? ? ? ? ? ? ? ? current->comm, task_pid_nr(current)); > >> + ? ? ? ? ? ? goto out; > >> + ? ? } > >> + > >> + ? ? /* execve is never allowed. */ > >> + ? ? if (syscall_is_execve(syscall)) > >> + ? ? ? ? ? ? goto out; > >> + > >> + ? ? ret = 0; > >> + ? ? id = seccomp_filter_id(filters, syscall); > >> + ? ? if (seccomp_filter_allow(id)) > >> + ? ? ? ? ? ? goto out; > >> + > >> + ? ? ret = -EACCES; > >> + ? ? if (!seccomp_filter_dynamic(id)) > >> + ? ? ? ? ? ? goto out; > >> + > >> + ? ? filter = seccomp_dynamic_filter(filters, id); > >> + ? ? if (filter && filter_match_current(filter)) > >> + ? ? ? ? ? ? ret = 0; > >> +out: > >> + ? ? put_seccomp_filters(filters); > >> + ? ? return ret; > >> +} > >> + > >> +/** > >> + * seccomp_show_filters - prints the current filter state to a seq_file > >> + * @filters: properly get()'d filters object > >> + * @m: the prepared seq_file to receive the data > >> + * > >> + * Returns 0 on a successful write. > >> + */ > >> +int seccomp_show_filters(struct seccomp_filters *filters, struct seq_file *m) > >> +{ > >> + ? ? int syscall; > >> + ? ? seq_printf(m, "Mode: %d\n", current->seccomp.mode); > >> + ? ? if (!filters) > >> + ? ? ? ? ? ? goto out; > >> + > >> + ? ? for (syscall = 0; syscall < NR_syscalls; ++syscall) { > >> + ? ? ? ? ? ? uint16_t id = seccomp_filter_id(filters, syscall); > >> + ? ? ? ? ? ? const char *filter_string = SECCOMP_FILTER_ALLOW; > >> + ? ? ? ? ? ? if (seccomp_filter_deny(id)) > >> + ? ? ? ? ? ? ? ? ? ? continue; > >> + ? ? ? ? ? ? seq_printf(m, "%d (%s): ", > >> + ? ? ? ? ? ? ? ? ? ? ? ? ? syscall, > >> + ? ? ? ? ? ? ? ? ? ? ? ? ? syscall_nr_to_name(syscall)); > >> + ? ? ? ? ? ? if (seccomp_filter_dynamic(id)) > >> + ? ? ? ? ? ? ? ? ? ? filter_string = get_filter_string( > >> + ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? seccomp_dynamic_filter(filters, id)); > >> + ? ? ? ? ? ? seq_printf(m, "%s\n", filter_string); > >> + ? ? } > >> +out: > >> + ? ? return 0; > >> +} > >> +EXPORT_SYMBOL_GPL(seccomp_show_filters); > >> + > >> +/** > >> + * seccomp_get_filter - copies the filter_string into "buf" > >> + * @syscall_nr: system call number to look up > >> + * @buf: destination buffer > >> + * @bufsize: available space in the buffer. > >> + * > >> + * Context: User context only. This function may sleep on allocation and > >> + * ? ? ? ? ?operates on current. current must be attempting a system call > >> + * ? ? ? ? ?when this is called. > >> + * > >> + * Looks up the filter for the given system call number on current. ?If found, > >> + * the string length of the NUL-terminated buffer is returned and < 0 is > >> + * returned on error. The NUL byte is not included in the length. > >> + */ > >> +long seccomp_get_filter(int syscall_nr, char *buf, unsigned long bufsize) > >> +{ > >> + ? ? struct seccomp_filters *filters; > >> + ? ? struct event_filter *filter; > >> + ? ? long ret = -EINVAL; > >> + ? ? uint16_t id; > >> + > >> + ? ? if (bufsize > SECCOMP_MAX_FILTER_LENGTH) > >> + ? ? ? ? ? ? bufsize = SECCOMP_MAX_FILTER_LENGTH; > >> + > >> + ? ? rcu_read_lock(); > >> + ? ? filters = get_seccomp_filters(current->seccomp.filters); > >> + ? ? rcu_read_unlock(); > >> + > >> + ? ? if (!filters) > >> + ? ? ? ? ? ? goto out; > >> + > >> + ? ? ret = -ENOENT; > >> + ? ? id = seccomp_filter_id(filters, syscall_nr); > >> + ? ? if (seccomp_filter_deny(id)) > >> + ? ? ? ? ? ? goto out; > >> + > >> + ? ? if (seccomp_filter_allow(id)) { > >> + ? ? ? ? ? ? ret = strlcpy(buf, SECCOMP_FILTER_ALLOW, bufsize); > >> + ? ? ? ? ? ? goto copied; > >> + ? ? } > >> + > >> + ? ? filter = seccomp_dynamic_filter(filters, id); > >> + ? ? if (!filter) > >> + ? ? ? ? ? ? goto out; > >> + ? ? ret = strlcpy(buf, get_filter_string(filter), bufsize); > >> + > >> +copied: > >> + ? ? if (ret >= bufsize) { > >> + ? ? ? ? ? ? ret = -ENOSPC; > >> + ? ? ? ? ? ? goto out; > >> + ? ? } > >> + ? ? /* Zero out any remaining buffer, just in case. */ > >> + ? ? memset(buf + ret, 0, bufsize - ret); > >> +out: > >> + ? ? put_seccomp_filters(filters); > >> + ? ? return ret; > >> +} > >> +EXPORT_SYMBOL_GPL(seccomp_get_filter); > >> + > >> +/** > >> + * seccomp_clear_filter: clears the seccomp filter for a syscall. > >> + * @syscall_nr: the system call number to clear filters for. > >> + * > >> + * Context: User context only. This function may sleep on allocation and > >> + * ? ? ? ? ?operates on current. current must be attempting a system call > >> + * ? ? ? ? ?when this is called. > >> + * > >> + * Returns 0 on success. > >> + */ > >> +long seccomp_clear_filter(int syscall_nr) > >> +{ > >> + ? ? struct seccomp_filters *filters = NULL, *orig_filters; > >> + ? ? uint16_t id; > >> + ? ? int ret = -EINVAL; > >> + > >> + ? ? rcu_read_lock(); > >> + ? ? orig_filters = get_seccomp_filters(current->seccomp.filters); > >> + ? ? rcu_read_unlock(); > >> + > >> + ? ? if (!orig_filters) > >> + ? ? ? ? ? ? goto out; > >> + > >> + ? ? if (filters_compat_mismatch(orig_filters)) > >> + ? ? ? ? ? ? goto out; > >> + > >> + ? ? id = seccomp_filter_id(orig_filters, syscall_nr); > >> + ? ? if (seccomp_filter_deny(id)) > >> + ? ? ? ? ? ? goto out; > >> + > >> + ? ? /* Create a new filters object for the task */ > >> + ? ? if (seccomp_filter_dynamic(id)) > >> + ? ? ? ? ? ? filters = seccomp_filters_new(orig_filters->count - 1); > >> + ? ? else > >> + ? ? ? ? ? ? filters = seccomp_filters_new(orig_filters->count); > >> + > >> + ? ? if (IS_ERR(filters)) { > >> + ? ? ? ? ? ? ret = PTR_ERR(filters); > >> + ? ? ? ? ? ? goto out; > >> + ? ? } > >> + > >> + ? ? /* Copy, but drop the requested entry. */ > >> + ? ? ret = seccomp_filters_copy(filters, orig_filters, syscall_nr); > >> + ? ? if (ret) > >> + ? ? ? ? ? ? goto out; > >> + ? ? get_seccomp_filters(filters); ?/* simplify the out: path */ > >> + > >> + ? ? rcu_assign_pointer(current->seccomp.filters, filters); > > > > What prevents two copies of seccomp_clear_filter() from running > > concurrently? > > Nothing - the last one wins assignment, but the objects themselves > should be internally consistent to the parallel calls. If that's a > concern, a per-task writer mutex could be used just to ensure > simultaneous calls to clear and set are performed serially. Would > that make more sense? Here is the sequence of events that I am concerned about: o CPU 0 sets orig_filters to point to the current filters. o CPU 1 sets its local orig_filters to point to the current set of filters. o Both CPUs allocate new filters and use rcu_assign_pointer() to do the update. As you say, the last one wins, but it appears to me that the first one leaks memory. o Both CPUs free the object referenced by their orig_filters, which might or might not result in a double free, depending on exactly what happens below. (You might actually be OK, I didn't check -- leaking memory was enough for me to call attention to this.) So yes, please use some kind of mutual exclusion. Not sure what you mean by "per-task mutex", but whatever it is must prevent two different tasks from acting on the same set of filters at the same time. The thing that I call "per-task mutex" would -not- do that. > >> + ? ? synchronize_rcu(); > >> + ? ? put_seccomp_filters(orig_filters); ?/* for the task */ > >> +out: > >> + ? ? put_seccomp_filters(orig_filters); ?/* for the get */ > >> + ? ? put_seccomp_filters(filters); ?/* for the extra get */ > >> + ? ? return ret; > >> +} > >> +EXPORT_SYMBOL_GPL(seccomp_clear_filter); > >> + > >> +/** > >> + * seccomp_set_filter: - Adds/extends a seccomp filter for a syscall. > >> + * @syscall_nr: system call number to apply the filter to. > >> + * @filter: ftrace filter string to apply. > >> + * > >> + * Context: User context only. This function may sleep on allocation and > >> + * ? ? ? ? ?operates on current. current must be attempting a system call > >> + * ? ? ? ? ?when this is called. > >> + * > >> + * New filters may be added for system calls when the current task is > >> + * not in a secure computing mode (seccomp). ?Otherwise, existing filters may > >> + * be extended. > >> + * > >> + * Returns 0 on success or an errno on failure. > >> + */ > >> +long seccomp_set_filter(int syscall_nr, char *filter) > >> +{ > >> + ? ? struct seccomp_filters *filters = NULL, *orig_filters = NULL; > >> + ? ? uint16_t id; > >> + ? ? long ret = -EINVAL; > >> + ? ? uint16_t filters_needed; > >> + > >> + ? ? if (!filter) > >> + ? ? ? ? ? ? goto out; > >> + > >> + ? ? filter = strstrip(filter); > >> + ? ? /* Disallow empty strings. */ > >> + ? ? if (filter[0] == 0) > >> + ? ? ? ? ? ? goto out; > >> + > >> + ? ? rcu_read_lock(); > >> + ? ? orig_filters = get_seccomp_filters(current->seccomp.filters); > >> + ? ? rcu_read_unlock(); > >> + > >> + ? ? /* After the first call, compatibility mode is selected permanently. */ > >> + ? ? ret = -EACCES; > >> + ? ? if (filters_compat_mismatch(orig_filters)) > >> + ? ? ? ? ? ? goto out; > >> + > >> + ? ? filters_needed = orig_filters ? orig_filters->count : 0; > >> + ? ? id = seccomp_filter_id(orig_filters, syscall_nr); > >> + ? ? if (seccomp_filter_deny(id)) { > >> + ? ? ? ? ? ? /* Don't allow DENYs to be changed when in a seccomp mode */ > >> + ? ? ? ? ? ? ret = -EACCES; > >> + ? ? ? ? ? ? if (current->seccomp.mode) > >> + ? ? ? ? ? ? ? ? ? ? goto out; > >> + ? ? ? ? ? ? filters_needed++; > >> + ? ? } > >> + > >> + ? ? filters = seccomp_filters_new(filters_needed); > >> + ? ? if (IS_ERR(filters)) { > >> + ? ? ? ? ? ? ret = PTR_ERR(filters); > >> + ? ? ? ? ? ? goto out; > >> + ? ? } > >> + > >> + ? ? filters_set_compat(filters); > >> + ? ? if (orig_filters) { > >> + ? ? ? ? ? ? ret = seccomp_filters_copy(filters, orig_filters, -1); > >> + ? ? ? ? ? ? if (ret) > >> + ? ? ? ? ? ? ? ? ? ? goto out; > >> + ? ? } > >> + > >> + ? ? if (seccomp_filter_deny(id)) > >> + ? ? ? ? ? ? ret = seccomp_add_filter(filters, syscall_nr, filter); > >> + ? ? else > >> + ? ? ? ? ? ? ret = seccomp_extend_filter(filters, syscall_nr, filter); > >> + ? ? if (ret) > >> + ? ? ? ? ? ? goto out; > >> + ? ? get_seccomp_filters(filters); ?/* simplify the error paths */ > >> + > >> + ? ? rcu_assign_pointer(current->seccomp.filters, filters); > > > > Again, what prevents two copies of seccomp_set_filter() from running > > concurrently? > > Same deal - nothing, but I'd be happy to add a guard if it makes sense. > > Thanks! > > >> + ? ? synchronize_rcu(); > >> + ? ? put_seccomp_filters(orig_filters); ?/* for the task */ > >> +out: > >> + ? ? put_seccomp_filters(orig_filters); ?/* for the get */ > >> + ? ? put_seccomp_filters(filters); ?/* for get or task, on err */ > >> + ? ? return ret; > >> +} > >> +EXPORT_SYMBOL_GPL(seccomp_set_filter); > >> + > >> +long prctl_set_seccomp_filter(unsigned long syscall_nr, > >> + ? ? ? ? ? ? ? ? ? ? ? ? ? char __user *user_filter) > >> +{ > >> + ? ? int nr; > >> + ? ? long ret; > >> + ? ? char *filter = NULL; > >> + > >> + ? ? ret = -EINVAL; > >> + ? ? if (syscall_nr >= NR_syscalls) > >> + ? ? ? ? ? ? goto out; > >> + > >> + ? ? ret = -EFAULT; > >> + ? ? if (!user_filter) > >> + ? ? ? ? ? ? goto out; > >> + > >> + ? ? filter = kzalloc(SECCOMP_MAX_FILTER_LENGTH + 1, GFP_KERNEL); > >> + ? ? ret = -ENOMEM; > >> + ? ? if (!filter) > >> + ? ? ? ? ? ? goto out; > >> + > >> + ? ? ret = -EFAULT; > >> + ? ? if (strncpy_from_user(filter, user_filter, > >> + ? ? ? ? ? ? ? ? ? ? ? ? ? SECCOMP_MAX_FILTER_LENGTH - 1) < 0) > >> + ? ? ? ? ? ? goto out; > >> + > >> + ? ? nr = (int) syscall_nr; > >> + ? ? ret = seccomp_set_filter(nr, filter); > >> + > >> +out: > >> + ? ? kfree(filter); > >> + ? ? return ret; > >> +} > >> + > >> +long prctl_clear_seccomp_filter(unsigned long syscall_nr) > >> +{ > >> + ? ? int nr = -1; > >> + ? ? long ret; > >> + > >> + ? ? ret = -EINVAL; > >> + ? ? if (syscall_nr >= NR_syscalls) > >> + ? ? ? ? ? ? goto out; > >> + > >> + ? ? nr = (int) syscall_nr; > >> + ? ? ret = seccomp_clear_filter(nr); > >> + > >> +out: > >> + ? ? return ret; > >> +} > >> + > >> +long prctl_get_seccomp_filter(unsigned long syscall_nr, char __user *dst, > >> + ? ? ? ? ? ? ? ? ? ? ? ? ? unsigned long available) > >> +{ > >> + ? ? int ret, nr; > >> + ? ? unsigned long copied; > >> + ? ? char *buf = NULL; > >> + ? ? ret = -EINVAL; > >> + ? ? if (!available) > >> + ? ? ? ? ? ? goto out; > >> + ? ? /* Ignore extra buffer space. */ > >> + ? ? if (available > SECCOMP_MAX_FILTER_LENGTH) > >> + ? ? ? ? ? ? available = SECCOMP_MAX_FILTER_LENGTH; > >> + > >> + ? ? ret = -EINVAL; > >> + ? ? if (syscall_nr >= NR_syscalls) > >> + ? ? ? ? ? ? goto out; > >> + ? ? nr = (int) syscall_nr; > >> + > >> + ? ? ret = -ENOMEM; > >> + ? ? buf = kmalloc(available, GFP_KERNEL); > >> + ? ? if (!buf) > >> + ? ? ? ? ? ? goto out; > >> + > >> + ? ? ret = seccomp_get_filter(nr, buf, available); > >> + ? ? if (ret < 0) > >> + ? ? ? ? ? ? goto out; > >> + > >> + ? ? /* Include the NUL byte in the copy. */ > >> + ? ? copied = copy_to_user(dst, buf, ret + 1); > >> + ? ? ret = -ENOSPC; > >> + ? ? if (copied) > >> + ? ? ? ? ? ? goto out; > >> + ? ? ret = 0; > >> +out: > >> + ? ? kfree(buf); > >> + ? ? return ret; > >> +} > >> diff --git a/kernel/sys.c b/kernel/sys.c > >> index af468ed..ed60d06 100644 > >> --- a/kernel/sys.c > >> +++ b/kernel/sys.c > >> @@ -1698,13 +1698,24 @@ SYSCALL_DEFINE5(prctl, int, option, unsigned long, arg2, unsigned long, arg3, > >> ? ? ? ? ? ? ? case PR_SET_ENDIAN: > >> ? ? ? ? ? ? ? ? ? ? ? error = SET_ENDIAN(me, arg2); > >> ? ? ? ? ? ? ? ? ? ? ? break; > >> - > >> ? ? ? ? ? ? ? case PR_GET_SECCOMP: > >> ? ? ? ? ? ? ? ? ? ? ? error = prctl_get_seccomp(); > >> ? ? ? ? ? ? ? ? ? ? ? break; > >> ? ? ? ? ? ? ? case PR_SET_SECCOMP: > >> ? ? ? ? ? ? ? ? ? ? ? error = prctl_set_seccomp(arg2); > >> ? ? ? ? ? ? ? ? ? ? ? break; > >> + ? ? ? ? ? ? case PR_SET_SECCOMP_FILTER: > >> + ? ? ? ? ? ? ? ? ? ? error = prctl_set_seccomp_filter(arg2, > >> + ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ?(char __user *) arg3); > >> + ? ? ? ? ? ? ? ? ? ? break; > >> + ? ? ? ? ? ? case PR_CLEAR_SECCOMP_FILTER: > >> + ? ? ? ? ? ? ? ? ? ? error = prctl_clear_seccomp_filter(arg2); > >> + ? ? ? ? ? ? ? ? ? ? break; > >> + ? ? ? ? ? ? case PR_GET_SECCOMP_FILTER: > >> + ? ? ? ? ? ? ? ? ? ? error = prctl_get_seccomp_filter(arg2, > >> + ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ?(char __user *) arg3, > >> + ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ?arg4); > >> + ? ? ? ? ? ? ? ? ? ? break; > >> ? ? ? ? ? ? ? case PR_GET_TSC: > >> ? ? ? ? ? ? ? ? ? ? ? error = GET_TSC_CTL(arg2); > >> ? ? ? ? ? ? ? ? ? ? ? break; > >> diff --git a/security/Kconfig b/security/Kconfig > >> index 95accd4..c76adf2 100644 > >> --- a/security/Kconfig > >> +++ b/security/Kconfig > >> @@ -2,6 +2,10 @@ > >> ?# Security configuration > >> ?# > >> > >> +# Make seccomp filter Kconfig switch below available > >> +config HAVE_SECCOMP_FILTER > >> + ? ? ? bool > >> + > >> ?menu "Security options" > >> > >> ?config KEYS > >> @@ -82,6 +86,19 @@ config SECURITY_DMESG_RESTRICT > >> > >> ? ? ? ? If you are unsure how to answer this question, answer N. > >> > >> +config SECCOMP_FILTER > >> + ? ? bool "Enable seccomp-based system call filtering" > >> + ? ? select SECCOMP > >> + ? ? depends on HAVE_SECCOMP_FILTER && EXPERIMENTAL > >> + ? ? help > >> + ? ? ? This kernel feature expands CONFIG_SECCOMP to allow computing > >> + ? ? ? in environments with reduced kernel access dictated by the > >> + ? ? ? application itself through prctl calls. ?If > >> + ? ? ? CONFIG_FTRACE_SYSCALLS is available, then system call > >> + ? ? ? argument-based filtering predicates may be used. > >> + > >> + ? ? ? See Documentation/prctl/seccomp_filter.txt for more detail. > >> + > >> ?config SECURITY > >> ? ? ? bool "Enable different security models" > >> ? ? ? depends on SYSFS > >> -- > >> 1.7.0.4 > >> > >> -- > >> To unsubscribe from this list: send the line "unsubscribe linux-kernel" in > >> the body of a message to majordomo@vger.kernel.org > >> More majordomo info at ?http://vger.kernel.org/majordomo-info.html > >> Please read the FAQ at ?http://www.tux.org/lkml/ > > > -- > To unsubscribe from this list: send the line "unsubscribe linux-kernel" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html > Please read the FAQ at http://www.tux.org/lkml/ -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/