From 789697007799297173bfb388cc7a71417b31273a Mon Sep 17 00:00:00 2001 From: Takashi Iwai Date: Thu, 22 Mar 2018 10:40:27 +0100 Subject: [PATCH] ALSA: aloop: Fix access to not-yet-ready substream via cable 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: Signed-off-by: Takashi Iwai Signed-off-by: Greg Kroah-Hartman --- sound/drivers/aloop.c | 8 +++++++- 1 file changed, 7 insertions(+), 1 deletion(-) diff --git a/sound/drivers/aloop.c b/sound/drivers/aloop.c index 610d36b..dc91002 100644 --- a/sound/drivers/aloop.c +++ b/sound/drivers/aloop.c @@ -666,7 +666,9 @@ static void free_cable(struct snd_pcm_substream *substream) 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_substream *substream) 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_substream *substream) 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); -- 2.7.4