On Sun, 24 Jan 2016 11:26:47 +0100, Dmitry Vyukov wrote:

Hello,

The following program triggers WARNING in snd_seq_oss_synth_cleanup:

------------[ cut here ]------------ WARNING: CPU: 1 PID: 7573 at sound/core/seq/oss/seq_oss_synth.c:311 snd_seq_oss_synth_cleanup+0x35f/0x420() Modules linked in: CPU: 1 PID: 7573 Comm: a.out Tainted: G W 4.4.0+ #276 Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011 00000000ffffffff ffff880036bcfbb0 ffffffff82999e2d 0000000000000000 ffff8800339797c0 ffffffff86d46580 ffff880036bcfbf0 ffffffff81352089 ffffffff84fd380f ffffffff86d46580 0000000000000137 ffff880033e592e8 Call Trace: [< inline >] __dump_stack lib/dump_stack.c:15 [<ffffffff82999e2d>] dump_stack+0x6f/0xa2 lib/dump_stack.c:50 [<ffffffff81352089>] warn_slowpath_common+0xd9/0x140 kernel/panic.c:482 [<ffffffff813522b9>] warn_slowpath_null+0x29/0x30 kernel/panic.c:515 [<ffffffff84fd380f>] snd_seq_oss_synth_cleanup+0x35f/0x420 sound/core/seq/oss/seq_oss_synth.c:311 [<ffffffff84fca919>] snd_seq_oss_release+0x79/0x130 sound/core/seq/oss/seq_oss_init.c:427 [<ffffffff84fc8faa>] odev_release+0x5a/0x80 sound/core/seq/oss/seq_oss.c:155 [<ffffffff817b73c6>] __fput+0x236/0x780 fs/file_table.c:208 [<ffffffff817b7995>] ____fput+0x15/0x20 fs/file_table.c:244 [<ffffffff813afdc0>] task_work_run+0x170/0x210 kernel/task_work.c:115 [< inline >] exit_task_work include/linux/task_work.h:21 [<ffffffff8135b275>] do_exit+0x8b5/0x2c60 kernel/exit.c:750 [<ffffffff8135d798>] do_group_exit+0x108/0x330 kernel/exit.c:880 [< inline >] SYSC_exit_group kernel/exit.c:891 [<ffffffff8135d9dd>] SyS_exit_group+0x1d/0x20 kernel/exit.c:889 [<ffffffff86336c36>] entry_SYSCALL_64_fastpath+0x16/0x7a arch/x86/entry/entry_64.S:185 ---[ end trace e71270304b7f911a ]---

// autogenerated by syzkaller (http://github.com/google/syzkaller) #include <sys/types.h> #include <sys/stat.h> #include <fcntl.h>

int main() { open("/dev/char/14:8", O_RDWR); }

On commit 30f05309bde49295e02e45c7e615f73aa4e0ccc2.

This must be an off-by-one error. The fix patch is below.

thanks,

Takashi

-- 8< -- From: Takashi Iwai tiwai@suse.de Subject: [PATCH] ALSA: seq: Fix incorrect sanity check at snd_seq_oss_synth_cleanup()

ALSA sequencer OSS emulation code has a sanity check for currently opened devices, but there is a thinko there, eventually it spews warnings and skips the operation wrongly.

Fix this off-by-one error.

Reported-by: Dmitry Vyukov dvyukov@google.com Cc: stable@vger.kernel.org Signed-off-by: Takashi Iwai tiwai@suse.de --- sound/core/seq/oss/seq_oss_synth.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/sound/core/seq/oss/seq_oss_synth.c b/sound/core/seq/oss/seq_oss_synth.c index 0f3b38184fe5..b16dbef04174 100644 --- a/sound/core/seq/oss/seq_oss_synth.c +++ b/sound/core/seq/oss/seq_oss_synth.c @@ -308,7 +308,7 @@ snd_seq_oss_synth_cleanup(struct seq_oss_devinfo *dp) struct seq_oss_synth *rec; struct seq_oss_synthinfo *info;

- if (snd_BUG_ON(dp->max_synthdev >= SNDRV_SEQ_OSS_MAX_SYNTH_DEVS)) + if (snd_BUG_ON(dp->max_synthdev > SNDRV_SEQ_OSS_MAX_SYNTH_DEVS)) return; for (i = 0; i < dp->max_synthdev; i++) { info = &dp->synths[i];