[tip:timers/urgent] posix-timer: Don't call idr_find() with out-of-range ID

From: tip-bot for Tejun Heo
Date: Thu Feb 21 2013 - 11:39:48 EST

Commit-ID: e182bb38d7db7494fa5dcd82da17fe0dedf60ecf
Gitweb: http://git.kernel.org/tip/e182bb38d7db7494fa5dcd82da17fe0dedf60ecf
Author: Tejun Heo <tj@xxxxxxxxxx>
AuthorDate: Wed, 20 Feb 2013 15:24:12 -0800
Committer: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
CommitDate: Thu, 21 Feb 2013 17:28:29 +0100

posix-timer: Don't call idr_find() with out-of-range ID

When idr_find() was fed a negative ID, it used to look up the ID
ignoring the sign bit before recent ("idr: remove MAX_IDR_MASK and
move left MAX_IDR_* into idr.c") patch. Now a negative ID triggers

__lock_timer() feeds timer_id from userland directly to idr_find()
without sanitizing it which can trigger the above malfunctions. Add a
range check on @timer_id before invoking idr_find() in __lock_timer().

While timer_t is defined as int by all archs at the moment, Andrew
worries that it may be defined as a larger type later on. Make the
test cover larger integers too so that it at least is guaranteed to
not return the wrong timer.

Note that WARN_ON_ONCE() in idr_find() on id < 0 is transitional
precaution while moving away from ignoring MSB. Once it's gone we can
remove the guard as long as timer_t isn't larger than int.

Signed-off-by: Tejun Heo <tj@xxxxxxxxxx>nnn
Reported-by: Sasha Levin <sasha.levin@xxxxxxxxxx>
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx
Link: http://lkml.kernel.org/r/20130220232412.GL3570@xxxxxxxxxxxxxx
Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
kernel/posix-timers.c | 7 +++++++
1 file changed, 7 insertions(+)

diff --git a/kernel/posix-timers.c b/kernel/posix-timers.c
index 10349d5..7edfe4b 100644
--- a/kernel/posix-timers.c
+++ b/kernel/posix-timers.c
@@ -639,6 +639,13 @@ static struct k_itimer *__lock_timer(timer_t timer_id, unsigned long *flags)
struct k_itimer *timr;

+ /*
+ * timer_t could be any type >= int and we want to make sure any
+ * @timer_id outside positive int range fails lookup.
+ */
+ if ((unsigned long long)timer_id > INT_MAX)
+ return NULL;
timr = idr_find(&posix_timers_id, (int)timer_id);
if (timr) {
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