Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758051AbcKCPax (ORCPT ); Thu, 3 Nov 2016 11:30:53 -0400 Received: from mail-oi0-f65.google.com ([209.85.218.65]:33865 "EHLO mail-oi0-f65.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755952AbcKCPat (ORCPT ); Thu, 3 Nov 2016 11:30:49 -0400 From: Lafcadio Wluiki To: linux-kernel@vger.kernel.org Cc: Andrew Morton , Kees Cook Subject: [PATCH 2/2] procfs/tasks: add a simple per-task procfs hidepid= field Date: Thu, 3 Nov 2016 09:30:38 -0600 Message-Id: <1478187038-19954-2-git-send-email-wluikil@gmail.com> X-Mailer: git-send-email 2.7.4 In-Reply-To: <1478187038-19954-1-git-send-email-wluikil@gmail.com> References: <1478187038-19954-1-git-send-email-wluikil@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 6790 Lines: 185 (Third, rebased submission, since first two submissions yielded no replies.) This adds a new per-task hidepid= flag that is honored by procfs when presenting /proc to the user, in addition to the existing hidepid= mount option. So far, hidepid= was exclusively a per-pidns setting. Locking down a set of processes so that they cannot see other user's processes without affecting the rest of the system thus currently requires creation of a private PID namespace, with all the complexity it brings, including maintaining a stub init process as PID 1 and losing the ability to see processes of the same user on the rest of the system. With this patch all acesss and visibility checks in procfs now honour two fields: a) the existing hide_pid field in the PID namespace b) the new hide_pid in struct task_struct Access/visibility is only granted if both fields permit it; the more restrictive one wins. By default the new task_struct hide_pid value defaults to 0, which means behaviour is not changed from the status quo. Setting the per-process hide_pid value is done via a new PR_SET_HIDEPID prctl() option which takes the same three supported values as the hidepid= mount option. The per-process hide_pid may only be increased, never decreased, thus ensuring that once applied, processes can never escape such a hide_pid jail. When a process forks it inherits its parent's hide_pid value. Suggested usecase: let's say nginx runs as user "www-data". After dropping privileges it may now call: … prctl(PR_SET_HIDEPID, 2); … And from that point on neither nginx itself, nor any of its child processes may see processes in /proc anymore that belong to a different user than "www-data". Other services running on the same system remain unaffected. This should permit Linux distributions to more comprehensively lock down their services, as it allows an isolated opt-in for hidepid= for specific services. Previously hidepid= could only be set system-wide, and then specific services had to be excluded by group membership, essentially a more complex concept of opt-out. A test-tool that validates this functionality is available here: https://paste.fedoraproject.org/412975/71967605/ Signed-off-by: Lafcadio Wluiki --- fs/proc/array.c | 3 +++ fs/proc/base.c | 6 ++++-- include/linux/init_task.h | 1 + include/linux/sched.h | 1 + include/uapi/linux/prctl.h | 4 ++++ kernel/fork.c | 1 + kernel/sys.c | 10 ++++++++++ 7 files changed, 24 insertions(+), 2 deletions(-) diff --git a/fs/proc/array.c b/fs/proc/array.c index 81818ad..ea801e5 100644 --- a/fs/proc/array.c +++ b/fs/proc/array.c @@ -163,6 +163,7 @@ static inline void task_state(struct seq_file *m, struct pid_namespace *ns, const struct cred *cred; pid_t ppid, tpid = 0, tgid, ngid; unsigned int max_fds = 0; + int hide_pid; rcu_read_lock(); ppid = pid_alive(p) ? @@ -183,6 +184,7 @@ static inline void task_state(struct seq_file *m, struct pid_namespace *ns, task_lock(p); if (p->files) max_fds = files_fdtable(p->files)->max_fds; + hide_pid = p->hide_pid; task_unlock(p); rcu_read_unlock(); @@ -201,6 +203,7 @@ static inline void task_state(struct seq_file *m, struct pid_namespace *ns, seq_put_decimal_ull(m, "\t", from_kgid_munged(user_ns, cred->egid)); seq_put_decimal_ull(m, "\t", from_kgid_munged(user_ns, cred->sgid)); seq_put_decimal_ull(m, "\t", from_kgid_munged(user_ns, cred->fsgid)); + seq_put_decimal_ull(m, "\nHidePID:\t", hide_pid); seq_put_decimal_ull(m, "\nFDSize:\t", max_fds); seq_puts(m, "\nGroups:\t"); diff --git a/fs/proc/base.c b/fs/proc/base.c index ae5e13c..6c9a42b 100644 --- a/fs/proc/base.c +++ b/fs/proc/base.c @@ -709,7 +709,8 @@ static bool has_pid_permissions(struct pid_namespace *pid, struct task_struct *task, int hide_pid_min) { - if (pid->hide_pid < hide_pid_min) + if (pid->hide_pid < hide_pid_min && + current->hide_pid < hide_pid_min) return true; if (in_group_p(pid->pid_gid)) return true; @@ -730,7 +731,8 @@ static int proc_pid_permission(struct inode *inode, int mask) put_task_struct(task); if (!has_perms) { - if (pid->hide_pid == HIDEPID_INVISIBLE) { + if (pid->hide_pid == HIDEPID_INVISIBLE || + current->hide_pid == HIDEPID_INVISIBLE) { /* * Let's make getdents(), stat(), and open() * consistent with each other. If a process diff --git a/include/linux/init_task.h b/include/linux/init_task.h index 325f649..c87de0e 100644 --- a/include/linux/init_task.h +++ b/include/linux/init_task.h @@ -250,6 +250,7 @@ extern struct task_group root_task_group; .cpu_timers = INIT_CPU_TIMERS(tsk.cpu_timers), \ .pi_lock = __RAW_SPIN_LOCK_UNLOCKED(tsk.pi_lock), \ .timer_slack_ns = 50000, /* 50 usec default slack */ \ + .hide_pid = 0, \ .pids = { \ [PIDTYPE_PID] = INIT_PID_LINK(PIDTYPE_PID), \ [PIDTYPE_PGID] = INIT_PID_LINK(PIDTYPE_PGID), \ diff --git a/include/linux/sched.h b/include/linux/sched.h index 348f51b..3e8ca16 100644 --- a/include/linux/sched.h +++ b/include/linux/sched.h @@ -1572,6 +1572,7 @@ struct task_struct { /* unserialized, strictly 'current' */ unsigned in_execve:1; /* bit to tell LSMs we're in execve */ unsigned in_iowait:1; + unsigned hide_pid:2; /* per-process procfs hidepid= */ #if !defined(TIF_RESTORE_SIGMASK) unsigned restore_sigmask:1; #endif diff --git a/include/uapi/linux/prctl.h b/include/uapi/linux/prctl.h index a8d0759..ada62b6 100644 --- a/include/uapi/linux/prctl.h +++ b/include/uapi/linux/prctl.h @@ -197,4 +197,8 @@ struct prctl_mm_map { # define PR_CAP_AMBIENT_LOWER 3 # define PR_CAP_AMBIENT_CLEAR_ALL 4 +/* Per process, non-revokable procfs hidepid= option */ +#define PR_SET_HIDEPID 48 +#define PR_GET_HIDEPID 49 + #endif /* _LINUX_PRCTL_H */ diff --git a/kernel/fork.c b/kernel/fork.c index 623259f..d4fe951 100644 --- a/kernel/fork.c +++ b/kernel/fork.c @@ -1562,6 +1562,7 @@ static __latent_entropy struct task_struct *copy_process( #endif p->default_timer_slack_ns = current->timer_slack_ns; + p->hide_pid = current->hide_pid; task_io_accounting_init(&p->ioac); acct_clear_integrals(p); diff --git a/kernel/sys.c b/kernel/sys.c index 89d5be4..c0a1d3e 100644 --- a/kernel/sys.c +++ b/kernel/sys.c @@ -2270,6 +2270,16 @@ SYSCALL_DEFINE5(prctl, int, option, unsigned long, arg2, unsigned long, arg3, case PR_GET_FP_MODE: error = GET_FP_MODE(me); break; + case PR_SET_HIDEPID: + if (arg2 < HIDEPID_OFF || arg2 > HIDEPID_INVISIBLE) + return -EINVAL; + if (arg2 < me->hide_pid) + return -EPERM; + me->hide_pid = arg2; + break; + case PR_GET_HIDEPID: + error = put_user((int) me->hide_pid, (int __user *)arg2); + break; default: error = -EINVAL; break; -- 2.7.4