Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754568AbbFEVWj (ORCPT ); Fri, 5 Jun 2015 17:22:39 -0400 Received: from mail-ig0-f175.google.com ([209.85.213.175]:38273 "EHLO mail-ig0-f175.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754534AbbFEVWc (ORCPT ); Fri, 5 Jun 2015 17:22:32 -0400 From: Tycho Andersen To: linux-kernel@vger.kernel.org, linux-api@vger.kernel.org Cc: Tycho Andersen , Kees Cook , Andy Lutomirski , Will Drewry , Roland McGrath , Oleg Nesterov , Pavel Emelyanov , "Serge E. Hallyn" Subject: [PATCH v3] seccomp: add ptrace options for suspend/resume Date: Fri, 5 Jun 2015 15:21:52 -0600 Message-Id: <1433539312-3999-1-git-send-email-tycho.andersen@canonical.com> X-Mailer: git-send-email 2.1.4 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 6378 Lines: 183 This patch is the first step in enabling checkpoint/restore of processes with seccomp enabled. One of the things CRIU does while dumping tasks is inject code into them via ptrace to collect information that is only available to the process itself. However, if we are in a seccomp mode where these processes are prohibited from making these syscalls, then what CRIU does kills the task. This patch adds a new ptrace option, PTRACE_O_SUSPEND_SECCOMP, that enables a task from the init user namespace which has CAP_SYS_ADMIN and no seccomp filters to disable (and re-enable) seccomp filters for another task so that they can be successfully dumped (and restored). We restrict the set of processes that can disable seccomp through ptrace because although today ptrace can be used to bypass seccomp, there is some discussion of closing this loophole in the future and we would like this patch to not depend on that behavior and be future proofed for when it is removed. Note that seccomp can be suspended before any filters are actually installed; this behavior is useful on criu restore, so that we can suspend seccomp, restore the filters, unmap our restore code from the restored process' address space, and then resume the task by detaching and have the filters resumed as well. v2 changes: * require that the tracer have no seccomp filters installed * drop TIF_NOTSC manipulation from the patch * change from ptrace command to a ptrace option and use this ptrace option as the flag to check. This means that as soon as the tracer detaches/dies, seccomp is re-enabled and as a corrollary that one can not disable seccomp across PTRACE_ATTACHs. v3 changes: * get rid of various #ifdefs everywhere * report more sensible errors when PTRACE_O_SUSPEND_SECCOMP is incorrectly used Signed-off-by: Tycho Andersen CC: Kees Cook CC: Andy Lutomirski CC: Will Drewry CC: Roland McGrath CC: Oleg Nesterov CC: Pavel Emelyanov CC: Serge E. Hallyn --- include/linux/ptrace.h | 1 + include/linux/seccomp.h | 10 ++++++++++ include/uapi/linux/ptrace.h | 6 ++++-- kernel/ptrace.c | 10 ++++++++++ kernel/seccomp.c | 22 ++++++++++++++++++++++ 5 files changed, 47 insertions(+), 2 deletions(-) diff --git a/include/linux/ptrace.h b/include/linux/ptrace.h index 987a73a..061265f 100644 --- a/include/linux/ptrace.h +++ b/include/linux/ptrace.h @@ -34,6 +34,7 @@ #define PT_TRACE_SECCOMP PT_EVENT_FLAG(PTRACE_EVENT_SECCOMP) #define PT_EXITKILL (PTRACE_O_EXITKILL << PT_OPT_FLAG_SHIFT) +#define PT_SUSPEND_SECCOMP (PTRACE_O_SUSPEND_SECCOMP << PT_OPT_FLAG_SHIFT) /* single stepping state bits (used on ARM and PA-RISC) */ #define PT_SINGLESTEP_BIT 31 diff --git a/include/linux/seccomp.h b/include/linux/seccomp.h index a19ddac..1d55cd9 100644 --- a/include/linux/seccomp.h +++ b/include/linux/seccomp.h @@ -95,4 +95,14 @@ static inline void get_seccomp_filter(struct task_struct *tsk) return; } #endif /* CONFIG_SECCOMP_FILTER */ + +#ifdef CONFIG_CHECKPOINT_RESTORE +extern bool may_suspend_seccomp(void); +#else +static inline bool may_suspend_seccomp(void) +{ + return false; +} +#endif + #endif /* _LINUX_SECCOMP_H */ diff --git a/include/uapi/linux/ptrace.h b/include/uapi/linux/ptrace.h index cf1019e..a7a6979 100644 --- a/include/uapi/linux/ptrace.h +++ b/include/uapi/linux/ptrace.h @@ -89,9 +89,11 @@ struct ptrace_peeksiginfo_args { #define PTRACE_O_TRACESECCOMP (1 << PTRACE_EVENT_SECCOMP) /* eventless options */ -#define PTRACE_O_EXITKILL (1 << 20) +#define PTRACE_O_EXITKILL (1 << 20) +#define PTRACE_O_SUSPEND_SECCOMP (1 << 21) -#define PTRACE_O_MASK (0x000000ff | PTRACE_O_EXITKILL) +#define PTRACE_O_MASK (\ + 0x000000ff | PTRACE_O_EXITKILL | PTRACE_O_SUSPEND_SECCOMP) #include diff --git a/kernel/ptrace.c b/kernel/ptrace.c index c8e0e05..a860deb 100644 --- a/kernel/ptrace.c +++ b/kernel/ptrace.c @@ -15,6 +15,7 @@ #include #include #include +#include #include #include #include @@ -556,6 +557,15 @@ static int ptrace_setoptions(struct task_struct *child, unsigned long data) if (data & ~(unsigned long)PTRACE_O_MASK) return -EINVAL; + if (unlikely(data & PTRACE_O_SUSPEND_SECCOMP)) { + if (!config_enabled(CONFIG_CHECKPOINT_RESTORE) || + !config_enabled(CONFIG_SECCOMP)) + return -EINVAL; + + if (!may_suspend_seccomp()) + return -EPERM; + } + /* Avoid intermediate state when all opts are cleared */ flags = child->ptrace; flags &= ~(PTRACE_O_MASK << PT_OPT_FLAG_SHIFT); diff --git a/kernel/seccomp.c b/kernel/seccomp.c index 980fd26..cdd97f6 100644 --- a/kernel/seccomp.c +++ b/kernel/seccomp.c @@ -590,6 +590,10 @@ void secure_computing_strict(int this_syscall) { int mode = current->seccomp.mode; + if (config_enabled(CONFIG_CHECKPOINT_RESTORE) && + unlikely(current->ptrace & PT_SUSPEND_SECCOMP)) + return; + if (mode == 0) return; else if (mode == SECCOMP_MODE_STRICT) @@ -691,6 +695,10 @@ u32 seccomp_phase1(struct seccomp_data *sd) int this_syscall = sd ? sd->nr : syscall_get_nr(current, task_pt_regs(current)); + if (config_enabled(CONFIG_CHECKPOINT_RESTORE) && + unlikely(current->ptrace & PT_SUSPEND_SECCOMP)) + return SECCOMP_PHASE1_OK; + switch (mode) { case SECCOMP_MODE_STRICT: __secure_computing_strict(this_syscall); /* may call do_exit */ @@ -901,3 +909,17 @@ long prctl_set_seccomp(unsigned long seccomp_mode, char __user *filter) /* prctl interface doesn't have flags, so they are always zero. */ return do_seccomp(op, 0, uargs); } + +#ifdef CONFIG_CHECKPOINT_RESTORE +bool may_suspend_seccomp(void) +{ + if (!capable(CAP_SYS_ADMIN)) + return false; + + if (current->seccomp.mode != SECCOMP_MODE_DISABLED || + current->ptrace & PT_SUSPEND_SECCOMP) + return false; + + return true; +} +#endif /* CONFIG_CHECKPOINT_RESTORE */ -- 2.1.4 -- 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/