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proc: fix timerslack_ns CAP_SYS_NICE check when adjusting self 

In changing from checking ptrace_may_access(p, PTRACE_MODE_ATTACH_FSCREDS)
to capable(CAP_SYS_NICE), I missed that ptrace_my_access succeeds when p
== current, but the CAP_SYS_NICE doesn't.

Thus while the previous commit was intended to loosen the needed
privileges to modify a processes timerslack, it needlessly restricted a
task modifying its own timerslack via the proc/<tid>/timerslack_ns
(which is permitted also via the PR_SET_TIMERSLACK method).

This patch corrects this by checking if p == current before checking the
CAP_SYS_NICE value.

This patch applies on top of my two previous patches currently in -mm

Link: http://lkml.kernel.org/r/1471906870-28624-1-git-send-email-john.stultz@linaro.org
Signed-off-by: John Stultz <john.stultz@linaro.org>
Acked-by: 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>
This commit is contained in:
John Stultz 2016-10-07 17:02:33 -07:00 committed by Linus Torvalds
parent 904763e1fb
commit 4b2bd5fec0
1 changed files with 19 additions and 15 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

34
fs/proc/base.c
View File

@ -2280,15 +2280,17 @@ static ssize_t timerslack_ns_write(struct file *file, const char __user *buf,
if (!p)
return -ESRCH;
if (!capable(CAP_SYS_NICE)) {
count = -EPERM;
goto out;
}
if (p != current) {
if (!capable(CAP_SYS_NICE)) {
count = -EPERM;
goto out;
}
err = security_task_setscheduler(p);
if (err) {
count = err;
goto out;
err = security_task_setscheduler(p);
if (err) {
count = err;
goto out;
}
}
task_lock(p);
@ -2314,14 +2316,16 @@ static int timerslack_ns_show(struct seq_file *m, void *v)
if (!p)
return -ESRCH;
if (!capable(CAP_SYS_NICE)) {
err = -EPERM;
goto out;
}
if (p != current) {
err = security_task_getscheduler(p);
if (err)
goto out;
if (!capable(CAP_SYS_NICE)) {
err = -EPERM;
goto out;
}
err = security_task_getscheduler(p);
if (err)
goto out;
}
task_lock(p);
seq_printf(m, "%llu\n", p->timer_slack_ns);