diff mbox

[RESEND] proc: Fix timerslack_ns CAP_SYS_NICE check when adjusting self

Message ID 1471906870-28624-1-git-send-email-john.stultz@linaro.org
State New
Headers show

Commit Message

John Stultz Aug. 22, 2016, 11:01 p.m. UTC
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
privledges 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

Cc: Kees Cook <keescook@chromium.org>
Cc: "Serge E. Hallyn" <serge@hallyn.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
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>
Acked-by: Kees Cook <keescook@chromium.org>

Signed-off-by: John Stultz <john.stultz@linaro.org>

---
 fs/proc/base.c | 34 +++++++++++++++++++---------------
 1 file changed, 19 insertions(+), 15 deletions(-)

-- 
1.9.1

Comments

John Stultz Aug. 29, 2016, 6:28 p.m. UTC | #1
On Mon, Aug 22, 2016 at 4:01 PM, John Stultz <john.stultz@linaro.org> wrote:
> 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

> privledges 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


Ping? Any feedback or comments on this one?

thanks
-john
John Stultz Aug. 30, 2016, 11:36 p.m. UTC | #2
On Tue, Aug 30, 2016 at 4:06 PM, Andrew Morton
<akpm@linux-foundation.org> wrote:
> On Tue, 30 Aug 2016 18:46:23 -0400 Kees Cook <keescook@chromium.org> wrote:

>

>> On Mon, Aug 22, 2016 at 7:01 PM, John Stultz <john.stultz@linaro.org> wrote:

>> > 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

>> > privledges 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

>> >

>> > Cc: Kees Cook <keescook@chromium.org>

>> > Cc: "Serge E. Hallyn" <serge@hallyn.com>

>> > Cc: Andrew Morton <akpm@linux-foundation.org>

>> > 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>

>> > Acked-by: Kees Cook <keescook@chromium.org>

>> > Signed-off-by: John Stultz <john.stultz@linaro.org>

>>

>> Andrew, can you take this for v4.8?

>

> Well, it fixes

> proc-relax-proc-tid-timerslack_ns-capability-requirements.patch,

> somewhat.  And it textually depends on that.

>

> Do we want all of

>

> proc-relax-proc-tid-timerslack_ns-capability-requirements.patch

> proc-add-lsm-hook-checks-to-proc-tid-timerslack_ns.patch

> proc-fix-timerslack_ns-cap_sys_nice-check-when-adjusting-self.patch

>

> in 4.8?  If so, why?


No.. they're fine to wait for the 4.9 merge window. But you picking up
this last fix is appreciated!

thanks
-john
diff mbox

Patch

diff --git a/fs/proc/base.c b/fs/proc/base.c
index 02f8389..01c3c2d 100644
--- a/fs/proc/base.c
+++ b/fs/proc/base.c
@@ -2281,15 +2281,17 @@  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);
@@ -2315,14 +2317,16 @@  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);