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authorTakashi Iwai <tiwai@suse.de>2018-04-26 09:17:45 +0200
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2018-05-09 09:51:50 +0200
commitdfe7f043bcfccc02362958273cec0dacd1343244 (patch)
parente5e9a770cec20bb51a8024fbaa890e5d0bcbb521 (diff)
ALSA: seq: Fix races at MIDI encoding in snd_virmidi_output_trigger()
commit 8f22e52528cc372b218b5f100457469615c733ce upstream. The sequencer virmidi code has an open race at its output trigger callback: namely, virmidi keeps only one event packet for processing while it doesn't protect for concurrent output trigger calls. snd_virmidi_output_trigger() tries to process the previously unfinished event before starting encoding the given MIDI stream, but this is done without any lock. Meanwhile, if another rawmidi stream starts the output trigger, this proceeds further, and overwrites the event package that is being processed in another thread. This eventually corrupts and may lead to the invalid memory access if the event type is like SYSEX. The fix is just to move the spinlock to cover both the pending event and the new stream. The bug was spotted by a new fuzzer, RaceFuzzer. BugLink: http://lkml.kernel.org/r/20180426045223.GA15307@dragonet.kaist.ac.kr Reported-by: DaeRyong Jeong <threeearcat@gmail.com> Cc: <stable@vger.kernel.org> Signed-off-by: Takashi Iwai <tiwai@suse.de> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
1 files changed, 2 insertions, 2 deletions
diff --git a/sound/core/seq/seq_virmidi.c b/sound/core/seq/seq_virmidi.c
index f48a4cd24ffc..289ae6bb81d9 100644
--- a/sound/core/seq/seq_virmidi.c
+++ b/sound/core/seq/seq_virmidi.c
@@ -174,12 +174,12 @@ static void snd_virmidi_output_trigger(struct snd_rawmidi_substream *substream,
+ spin_lock_irqsave(&substream->runtime->lock, flags);
if (vmidi->event.type != SNDRV_SEQ_EVENT_NONE) {
if (snd_seq_kernel_client_dispatch(vmidi->client, &vmidi->event, in_atomic(), 0) < 0)
- return;
+ goto out;
vmidi->event.type = SNDRV_SEQ_EVENT_NONE;
- spin_lock_irqsave(&substream->runtime->lock, flags);
while (1) {
count = __snd_rawmidi_transmit_peek(substream, buf, sizeof(buf));
if (count <= 0)