diff options
author | John Stultz <john.stultz@linaro.org> | 2016-10-07 17:02:26 -0700 |
---|---|---|
committer | Linus Torvalds <torvalds@linux-foundation.org> | 2016-10-07 18:46:30 -0700 |
commit | 7abbaf94049914f074306d960b0f968ffe52e59f (patch) | |
tree | 8b0166be20e0400467cd7441783ba7b34b32985b | |
parent | e16e2d8e14a14bd87df8482c637dde8f760a8d5f (diff) |
proc: relax /proc/<tid>/timerslack_ns capability requirements
When an interface to allow a task to change another tasks timerslack was
first proposed, it was suggested that something greater then
CAP_SYS_NICE would be needed, as a task could be delayed further then
what normally could be done with nice adjustments.
So CAP_SYS_PTRACE was adopted instead for what became the
/proc/<tid>/timerslack_ns interface. However, for Android (where this
feature originates), giving the system_server CAP_SYS_PTRACE would allow
it to observe and modify all tasks memory. This is considered too high
a privilege level for only needing to change the timerslack.
After some discussion, it was realized that a CAP_SYS_NICE process can
set a task as SCHED_FIFO, so they could fork some spinning processes and
set them all SCHED_FIFO 99, in effect delaying all other tasks for an
infinite amount of time.
So as a CAP_SYS_NICE task can already cause trouble for other tasks,
using it as a required capability for accessing and modifying
/proc/<tid>/timerslack_ns seems sufficient.
Thus, this patch loosens the capability requirements to CAP_SYS_NICE and
removes CAP_SYS_PTRACE, simplifying some of the code flow as well.
This is technically an ABI change, but as the feature just landed in
4.6, I suspect no one is yet using it.
Link: http://lkml.kernel.org/r/1469132667-17377-1-git-send-email-john.stultz@linaro.org
Signed-off-by: John Stultz <john.stultz@linaro.org>
Reviewed-by: Nick Kralevich <nnk@google.com>
Acked-by: Serge Hallyn <serge@hallyn.com>
Acked-by: Kees Cook <keescook@chromium.org>
Cc: Kees Cook <keescook@chromium.org>
Cc: "Serge E. Hallyn" <serge@hallyn.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Arjan van de Ven <arjan@linux.intel.com>
Cc: Oren Laadan <orenl@cellrox.com>
Cc: Ruchi Kandoi <kandoiruchi@google.com>
Cc: Rom Lemarchand <romlem@android.com>
Cc: Todd Kjos <tkjos@google.com>
Cc: Colin Cross <ccross@android.com>
Cc: Nick Kralevich <nnk@google.com>
Cc: Dmitry Shmidt <dimitrysh@google.com>
Cc: Elliott Hughes <enh@google.com>
Cc: Android Kernel Team <kernel-team@android.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
-rw-r--r-- | fs/proc/base.c | 34 |
1 files changed, 20 insertions, 14 deletions
diff --git a/fs/proc/base.c b/fs/proc/base.c index 3b792ab3c0dc..248f008d46b8 100644 --- a/fs/proc/base.c +++ b/fs/proc/base.c @@ -2280,16 +2280,19 @@ static ssize_t timerslack_ns_write(struct file *file, const char __user *buf, if (!p) return -ESRCH; - if (ptrace_may_access(p, PTRACE_MODE_ATTACH_FSCREDS)) { - task_lock(p); - if (slack_ns == 0) - p->timer_slack_ns = p->default_timer_slack_ns; - else - p->timer_slack_ns = slack_ns; - task_unlock(p); - } else + if (!capable(CAP_SYS_NICE)) { count = -EPERM; + goto out; + } + task_lock(p); + if (slack_ns == 0) + p->timer_slack_ns = p->default_timer_slack_ns; + else + p->timer_slack_ns = slack_ns; + task_unlock(p); + +out: put_task_struct(p); return count; @@ -2299,19 +2302,22 @@ static int timerslack_ns_show(struct seq_file *m, void *v) { struct inode *inode = m->private; struct task_struct *p; - int err = 0; + int err = 0; p = get_proc_task(inode); if (!p) return -ESRCH; - if (ptrace_may_access(p, PTRACE_MODE_ATTACH_FSCREDS)) { - task_lock(p); - seq_printf(m, "%llu\n", p->timer_slack_ns); - task_unlock(p); - } else + if (!capable(CAP_SYS_NICE)) { err = -EPERM; + goto out; + } + task_lock(p); + seq_printf(m, "%llu\n", p->timer_slack_ns); + task_unlock(p); + +out: put_task_struct(p); return err; |