linux-kernel - [PATCH] posix-timers: Use array safe helper when fetching notification symbolic name

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Date:   Thu, 1 Nov 2018 21:27:23 +0300
From:   Cyrill Gorcunov <gorcunov@...il.com>
To:     LKML <linux-kernel@...r.kernel.org>
Cc:     Andrey Vagin <avagin@...il.com>,
        Thomas Gleixner <tglx@...utronix.de>
Subject: [PATCH] posix-timers: Use array safe helper when fetching
 notification symbolic name

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 in furher modifications.

Cc: Andrey Vagin <avagin@...il.com>
Cc: Thomas Gleixner <tglx@...utronix.de>
Signed-off-by: Cyrill Gorcunov <gorcunov@...il.com>
---
 fs/proc/base.c |    6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

Index: linux-ml.git/fs/proc/base.c
===================================================================
--- linux-ml.git.orig/fs/proc/base.c
+++ linux-ml.git/fs/proc/base.c
@@ -2287,7 +2287,7 @@ static int show_timer(struct seq_file *m
 {
 	struct k_itimer *timer;
 	struct timers_private *tp = m->private;
-	int notify;
+	int notify, nidx;
 	static const char * const nstr[] = {
 		[SIGEV_SIGNAL] = "signal",
 		[SIGEV_NONE] = "none",
@@ -2296,13 +2296,13 @@ static int show_timer(struct seq_file *m
 
 	timer = list_entry((struct list_head *)v, struct k_itimer, list);
 	notify = timer->it_sigev_notify;
+	nidx = array_index_nospec(notify & ~SIGEV_THREAD_ID, ARRAY_SIZE(nstr));
 
 	seq_printf(m, "ID: %d\n", timer->it_id);
 	seq_printf(m, "signal: %d/%px\n",
 		   timer->sigq->info.si_signo,
 		   timer->sigq->info.si_value.sival_ptr);
-	seq_printf(m, "notify: %s/%s.%d\n",
-		   nstr[notify & ~SIGEV_THREAD_ID],
+	seq_printf(m, "notify: %s/%s.%d\n", nstr[nidx],
 		   (notify & SIGEV_THREAD_ID) ? "tid" : "pid",
 		   pid_nr_ns(timer->it_pid, tp->ns));
 	seq_printf(m, "ClockID: %d\n", timer->it_clock);