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 <keesc...@chromium.org>
Cc: "Serge E. Hallyn" <se...@hallyn.com>
Cc: Andrew Morton <a...@linux-foundation.org>
Cc: Thomas Gleixner <t...@linutronix.de>
CC: Arjan van de Ven <ar...@linux.intel.com>
Cc: Oren Laadan <or...@cellrox.com>
Cc: Ruchi Kandoi <kandoiru...@google.com>
Cc: Rom Lemarchand <rom...@android.com>
Cc: Todd Kjos <tk...@google.com>
Cc: Colin Cross <ccr...@android.com>
Cc: Nick Kralevich <n...@google.com>
Cc: Dmitry Shmidt <dimitr...@google.com>
Cc: Elliott Hughes <e...@google.com>
Cc: Android Kernel Team <kernel-t...@android.com>
Signed-off-by: John Stultz <john.stu...@linaro.org>
---
fs/proc/base.c | 34 +++++++++++++++++++---------------
1 file changed, 19 insertions(+), 15 deletions(-)
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);
--
1.9.1
