linux-kernel - [PATCH 4.9 043/130] ALSA: seq: Fix UBSAN warning at SNDRV_SEQ_IOCTL_QUERY_NEXT

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Message-Id: <20180823074930.029296597@linuxfoundation.org>
Date:   Thu, 23 Aug 2018 09:52:39 +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>,
        Sasha Levin <alexander.levin@...rosoft.com>
Subject: [PATCH 4.9 043/130] ALSA: seq: Fix UBSAN warning at SNDRV_SEQ_IOCTL_QUERY_NEXT_CLIENT ioctl

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

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

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

[ Upstream commit c9a4c63888dbb79ce4d068ca1dd8b05bc3f156b1 ]

The kernel may spew a WARNING with UBSAN undefined behavior at
handling ALSA sequencer ioctl SNDRV_SEQ_IOCTL_QUERY_NEXT_CLIENT:

UBSAN: Undefined behaviour in sound/core/seq/seq_clientmgr.c:2007:14
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_seq_ioctl_query_next_client+0x1ac/0x1d0 sound/core/seq/seq_clientmgr.c:2007
 snd_seq_ioctl+0x264/0x3d0 sound/core/seq/seq_clientmgr.c:2144
 ....

It happens only when INT_MAX is passed there, 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=200211
Signed-off-by: Takashi Iwai <tiwai@...e.de>
Signed-off-by: Sasha Levin <alexander.levin@...rosoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 sound/core/seq/seq_clientmgr.c |    3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

--- a/sound/core/seq/seq_clientmgr.c
+++ b/sound/core/seq/seq_clientmgr.c
@@ -2002,7 +2002,8 @@ static int snd_seq_ioctl_query_next_clie
 	struct snd_seq_client *cptr = NULL;

 	/* search for next client */
-	info->client++;
+	if (info->client < INT_MAX)
+		info->client++;
 	if (info->client < 0)
 		info->client = 0;
 	for (; info->client < SNDRV_SEQ_MAX_CLIENTS; info->client++) {