From 4ba3dbc42a852bd0489b293024b133ed76d521c6 Mon Sep 17 00:00:00 2001 From: Takashi Iwai Date: Mon, 25 Jun 2018 11:09:11 +0200 Subject: [PATCH] ALSA: timer: Fix UBSAN warning at SNDRV_TIMER_IOCTL_NEXT_DEVICE ioctl commit b41f794f284966fd6ec634111e3b40d241389f96 upstream. The kernel may spew a WARNING about UBSAN undefined behavior at handling ALSA timer ioctl SNDRV_TIMER_IOCTL_NEXT_DEVICE: UBSAN: Undefined behaviour in sound/core/timer.c:1524:19 signed integer overflow: 2147483647 + 1 cannot be represented in type 'int' Call Trace: __dump_stack lib/dump_stack.c:77 [inline] dump_stack+0x122/0x1c8 lib/dump_stack.c:113 ubsan_epilogue+0x12/0x86 lib/ubsan.c:159 handle_overflow+0x1c2/0x21f lib/ubsan.c:190 __ubsan_handle_add_overflow+0x2a/0x31 lib/ubsan.c:198 snd_timer_user_next_device sound/core/timer.c:1524 [inline] __snd_timer_user_ioctl+0x204d/0x2520 sound/core/timer.c:1939 snd_timer_user_ioctl+0x67/0x95 sound/core/timer.c:1994 .... It happens only when a value with INT_MAX is passed, as we're incrementing it unconditionally. So the fix is trivial, check the value with INT_MAX. Although the bug itself is fairly harmless, it's better to fix it so that fuzzers won't hit this again later. Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=200213 Reported-and-tested-by: Team OWL337 Signed-off-by: Takashi Iwai [bwh: Backported to 3.16: adjust context, indentation] Signed-off-by: Ben Hutchings --- sound/core/timer.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/sound/core/timer.c b/sound/core/timer.c index 30857a7e2dc9..593deebd9da6 100644 --- a/sound/core/timer.c +++ b/sound/core/timer.c @@ -1462,7 +1462,7 @@ static int snd_timer_user_next_device(struct snd_timer_id __user *_tid) } else { if (id.subdevice < 0) { id.subdevice = 0; - } else { + } else if (id.subdevice < INT_MAX) { id.subdevice++; } }