4.4-stable review patch. If anyone has any objections, please let me know.
------------------
From: Takashi Iwai tiwai@suse.de
commit 8e6b1a72a75bb5067ccb6b56d8ca4aa3a300a64e upstream.
In loopback_open() and loopback_close(), we assign and release the substream object to the corresponding cable in a racy way. It's neither locked nor done in the right position. The open callback assigns the substream before its preparation finishes, hence the other side of the cable may pick it up, which may lead to the invalid memory access.
This patch addresses these: move the assignment to the end of the open callback, and wrap with cable->lock for avoiding concurrent accesses.
Cc: stable@vger.kernel.org Signed-off-by: Takashi Iwai tiwai@suse.de Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- sound/drivers/aloop.c | 8 +++++++- 1 file changed, 7 insertions(+), 1 deletion(-)
--- a/sound/drivers/aloop.c +++ b/sound/drivers/aloop.c @@ -666,7 +666,9 @@ static void free_cable(struct snd_pcm_su return; if (cable->streams[!substream->stream]) { /* other stream is still alive */ + spin_lock_irq(&cable->lock); cable->streams[substream->stream] = NULL; + spin_unlock_irq(&cable->lock); } else { /* free the cable */ loopback->cables[substream->number][dev] = NULL; @@ -706,7 +708,6 @@ static int loopback_open(struct snd_pcm_ loopback->cables[substream->number][dev] = cable; } dpcm->cable = cable; - cable->streams[substream->stream] = dpcm;
snd_pcm_hw_constraint_integer(runtime, SNDRV_PCM_HW_PARAM_PERIODS);
@@ -738,6 +739,11 @@ static int loopback_open(struct snd_pcm_ runtime->hw = loopback_pcm_hardware; else runtime->hw = cable->hw; + + spin_lock_irq(&cable->lock); + cable->streams[substream->stream] = dpcm; + spin_unlock_irq(&cable->lock); + unlock: if (err < 0) { free_cable(substream);