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authorTakashi Iwai <tiwai@suse.de>2019-07-15 22:50:27 +0200
committerTakashi Iwai <tiwai@suse.de>2019-07-16 09:41:41 +0200
commitede34f397ddb063b145b9e7d79c6026f819ded13 (patch)
treec4512b7219236a6268838215384de608eb3c992e /sound/core/seq
parent4b4e0e32e4b09274dbc9d173016c1a026f44608c (diff)
downloadblackbird-op-linux-ede34f397ddb063b145b9e7d79c6026f819ded13.tar.gz
blackbird-op-linux-ede34f397ddb063b145b9e7d79c6026f819ded13.zip
ALSA: seq: Break too long mutex context in the write loop
The fix for the racy writes and ioctls to sequencer widened the application of client->ioctl_mutex to the whole write loop. Although it does unlock/relock for the lengthy operation like the event dup, the loop keeps the ioctl_mutex for the whole time in other situations. This may take quite long time if the user-space would give a huge buffer, and this is a likely cause of some weird behavior spotted by syzcaller fuzzer. This patch puts a simple workaround, just adding a mutex break in the loop when a large number of events have been processed. This shouldn't hit any performance drop because the threshold is set high enough for usual operations. Fixes: 7bd800915677 ("ALSA: seq: More protection for concurrent write and ioctl races") Reported-by: syzbot+97aae04ce27e39cbfca9@syzkaller.appspotmail.com Reported-by: syzbot+4c595632b98bb8ffcc66@syzkaller.appspotmail.com Cc: <stable@vger.kernel.org> Signed-off-by: Takashi Iwai <tiwai@suse.de>
Diffstat (limited to 'sound/core/seq')
-rw-r--r--sound/core/seq/seq_clientmgr.c11
1 files changed, 10 insertions, 1 deletions
diff --git a/sound/core/seq/seq_clientmgr.c b/sound/core/seq/seq_clientmgr.c
index a60e7a17f0b8..7737b2670064 100644
--- a/sound/core/seq/seq_clientmgr.c
+++ b/sound/core/seq/seq_clientmgr.c
@@ -1021,7 +1021,7 @@ static ssize_t snd_seq_write(struct file *file, const char __user *buf,
{
struct snd_seq_client *client = file->private_data;
int written = 0, len;
- int err;
+ int err, handled;
struct snd_seq_event event;
if (!(snd_seq_file_flags(file) & SNDRV_SEQ_LFLG_OUTPUT))
@@ -1034,6 +1034,8 @@ static ssize_t snd_seq_write(struct file *file, const char __user *buf,
if (!client->accept_output || client->pool == NULL)
return -ENXIO;
+ repeat:
+ handled = 0;
/* allocate the pool now if the pool is not allocated yet */
mutex_lock(&client->ioctl_mutex);
if (client->pool->size > 0 && !snd_seq_write_pool_allocated(client)) {
@@ -1093,12 +1095,19 @@ static ssize_t snd_seq_write(struct file *file, const char __user *buf,
0, 0, &client->ioctl_mutex);
if (err < 0)
break;
+ handled++;
__skip_event:
/* Update pointers and counts */
count -= len;
buf += len;
written += len;
+
+ /* let's have a coffee break if too many events are queued */
+ if (++handled >= 200) {
+ mutex_unlock(&client->ioctl_mutex);
+ goto repeat;
+ }
}
out:
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