linux-kernel - [PATCH 4.14 147/157] ALSA: timer: Fix UBSAN warning at SNDRV_TIMER_IOCTL_NEXT

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Message-Id: <20180701160900.522711854@linuxfoundation.org>
Date:   Sun,  1 Jul 2018 18:23:39 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Takashi Iwai <tiwai@...e.de>
Subject: [PATCH 4.14 147/157] ALSA: timer: Fix UBSAN warning at SNDRV_TIMER_IOCTL_NEXT_DEVICE ioctl

4.14-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Takashi Iwai <tiwai@...e.de>

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 <icytxw@...il.com>
Cc: <stable@...r.kernel.org>
Signed-off-by: Takashi Iwai <tiwai@...e.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 sound/core/timer.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/sound/core/timer.c
+++ b/sound/core/timer.c
@@ -1514,7 +1514,7 @@ static int snd_timer_user_next_device(st
 				} else {
 					if (id.subdevice < 0)
 						id.subdevice = 0;
-					else
+					else if (id.subdevice < INT_MAX)
 						id.subdevice++;
 				}
 			}