[PATCH UPDATED] posix-timer: don't call idr_find() w/ out-of-range ID

[Tejun Heo]

When idr_find() is 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, and triggers WARN_ON_ONCE()
after it.

__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: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx
---
Given that larger timer_t is possible, at least theoretically, it
probably is better to keep the guard even if idr_find() is later
updated, so not marking the guard as to be removed.

Will send a separate patch to add comment on top of WARN_ON_ONCE() in
idr_find().

Thanks.

 kernel/posix-timers.c |    7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/kernel/posix-timers.c b/kernel/posix-timers.c
index b51bb08..6edbb2c 100644
--- a/kernel/posix-timers.c
+++ b/kernel/posix-timers.c
@@ -637,6 +637,13 @@ 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;
+
 	rcu_read_lock();
 	timr = idr_find(&posix_timers_id, (int)timer_id);
 	if (timr) {
--
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