[PATCH v2] fs/proc: timers -- Test for potential index overflow

[Cyrill Gorcunov]

When showing timer's notify symbolic name make sure we never fetch a value
sitting outside of the names array. Though the former issue displaying
timer->it_sigev_notify has been fixed by Thomas in commit cef31d9af9082434,
better to make sure we won't hit it again on furher modifications.

v2: Use explicit index overflow test (by tglx@). Since
    it should never happen add warn-once to notify.

Cc: Andrey Vagin <avagin@xxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Signed-off-by: Cyrill Gorcunov <gorcunov@xxxxxxxxx>
---
 fs/proc/base.c |    6 ++++++
 1 file changed, 6 insertions(+)

Index: linux-ml.git/fs/proc/base.c
===================================================================
--- linux-ml.git.orig/fs/proc/base.c
+++ linux-ml.git/fs/proc/base.c
@@ -2297,6 +2297,12 @@ static int show_timer(struct seq_file *m
 	timer = list_entry((struct list_head *)v, struct k_itimer, list);
 	notify = timer->it_sigev_notify;
 
+	if ((notify & ~SIGEV_THREAD_ID) >= ARRAY_SIZE(nstr)) {
+		WARN_ONCE(1, "timer: Bad signal notify mode %#x on ID %d\n",
+			  notify, timer->it_id);
+		return -EINVAL;
+	}
+
 	seq_printf(m, "ID: %d\n", timer->it_id);
 	seq_printf(m, "signal: %d/%px\n",
 		   timer->sigq->info.si_signo,