Although we apply the params_lock mutex to the whole read and write operations as well as snd_pcm_oss_change_params(), we may still face some races.

First off, the params_lock is taken inside the read and write loop. This is intentional for avoiding the too long locking, but it allows the in-between parameter change, which might lead to invalid pointers. We check the readiness of the stream and set up via snd_pcm_oss_make_ready() at the beginning of read and write, but it's called only once, by assuming that it remains ready in the rest.

Second, many ioctls that may change the actual parameters (i.e. setting runtime->oss.params=1) aren't protected, hence they can be processed in a half-baked state.

This patch is an attempt to plug these holes. The stream readiness check is moved inside the read/write inner loop, so that the stream is always set up in a proper state before further processing. Also, each ioctl that may change the parameter is wrapped with the params_lock for avoiding the races.

The issues were triggered by syzkaller in a few different scenarios, particularly the one below appearing as GPF in loopback_pos_update.

Reported-by: syzbot+c4227aec125487ec3efa@syzkaller.appspotmail.com Cc: stable@vger.kernel.org Signed-off-by: Takashi Iwai tiwai@suse.de --- sound/core/oss/pcm_oss.c | 134 +++++++++++++++++++++++++++++++++++++---------- 1 file changed, 106 insertions(+), 28 deletions(-)

diff --git a/sound/core/oss/pcm_oss.c b/sound/core/oss/pcm_oss.c index 02298c9c6020..f8bfee8022e0 100644 --- a/sound/core/oss/pcm_oss.c +++ b/sound/core/oss/pcm_oss.c @@ -823,8 +823,8 @@ static int choose_rate(struct snd_pcm_substream *substream, return snd_pcm_hw_param_near(substream, params, SNDRV_PCM_HW_PARAM_RATE, best_rate, NULL); }

-static int snd_pcm_oss_change_params(struct snd_pcm_substream *substream, - bool trylock) +/* call with params_lock held */ +static int snd_pcm_oss_change_params_locked(struct snd_pcm_substream *substream) { struct snd_pcm_runtime *runtime = substream->runtime; struct snd_pcm_hw_params *params, *sparams; @@ -838,11 +838,8 @@ static int snd_pcm_oss_change_params(struct snd_pcm_substream *substream, const struct snd_mask *sformat_mask; struct snd_mask mask;

- if (trylock) { - if (!(mutex_trylock(&runtime->oss.params_lock))) - return -EAGAIN; - } else if (mutex_lock_interruptible(&runtime->oss.params_lock)) - return -ERESTARTSYS; + if (!runtime->oss.params) + return 0; sw_params = kzalloc(sizeof(*sw_params), GFP_KERNEL); params = kmalloc(sizeof(*params), GFP_KERNEL); sparams = kmalloc(sizeof(*sparams), GFP_KERNEL); @@ -1068,6 +1065,23 @@ static int snd_pcm_oss_change_params(struct snd_pcm_substream *substream, kfree(sw_params); kfree(params); kfree(sparams); + return err; +} + +/* this one takes the lock by itself */ +static int snd_pcm_oss_change_params(struct snd_pcm_substream *substream, + bool trylock) +{ + struct snd_pcm_runtime *runtime = substream->runtime; + int err; + + if (trylock) { + if (!(mutex_trylock(&runtime->oss.params_lock))) + return -EAGAIN; + } else if (mutex_lock_interruptible(&runtime->oss.params_lock)) + return -ERESTARTSYS; + + err = snd_pcm_oss_change_params_locked(substream); mutex_unlock(&runtime->oss.params_lock); return err; } @@ -1096,11 +1110,14 @@ static int snd_pcm_oss_get_active_substream(struct snd_pcm_oss_file *pcm_oss_fil return 0; }

+/* call with params_lock held */ static int snd_pcm_oss_prepare(struct snd_pcm_substream *substream) { int err; struct snd_pcm_runtime *runtime = substream->runtime;

+ if (!runtime->oss.prepare) + return 0; err = snd_pcm_kernel_ioctl(substream, SNDRV_PCM_IOCTL_PREPARE, NULL); if (err < 0) { pcm_dbg(substream->pcm, @@ -1120,14 +1137,35 @@ static int snd_pcm_oss_make_ready(struct snd_pcm_substream *substream) struct snd_pcm_runtime *runtime; int err;

- if (substream == NULL) - return 0; runtime = substream->runtime; if (runtime->oss.params) { err = snd_pcm_oss_change_params(substream, false); if (err < 0) return err; } + if (runtime->oss.prepare) { + if (mutex_lock_interruptible(&runtime->oss.params_lock)) + return -ERESTARTSYS; + err = snd_pcm_oss_prepare(substream); + mutex_unlock(&runtime->oss.params_lock); + if (err < 0) + return err; + } + return 0; +} + +/* call with params_lock held */ +static int snd_pcm_oss_make_ready_locked(struct snd_pcm_substream *substream) +{ + struct snd_pcm_runtime *runtime; + int err; + + runtime = substream->runtime; + if (runtime->oss.params) { + err = snd_pcm_oss_change_params_locked(substream); + if (err < 0) + return err; + } if (runtime->oss.prepare) { err = snd_pcm_oss_prepare(substream); if (err < 0) @@ -1332,13 +1370,14 @@ static ssize_t snd_pcm_oss_write1(struct snd_pcm_substream *substream, const cha if (atomic_read(&substream->mmap_count)) return -ENXIO;

- if ((tmp = snd_pcm_oss_make_ready(substream)) < 0) - return tmp; while (bytes > 0) { if (mutex_lock_interruptible(&runtime->oss.params_lock)) { tmp = -ERESTARTSYS; break; } + tmp = snd_pcm_oss_make_ready_locked(substream); + if (tmp < 0) + goto err; if (bytes < runtime->oss.period_bytes || runtime->oss.buffer_used > 0) { tmp = bytes; if (tmp + runtime->oss.buffer_used > runtime->oss.period_bytes) @@ -1439,13 +1478,14 @@ static ssize_t snd_pcm_oss_read1(struct snd_pcm_substream *substream, char __use if (atomic_read(&substream->mmap_count)) return -ENXIO;

- if ((tmp = snd_pcm_oss_make_ready(substream)) < 0) - return tmp; while (bytes > 0) { if (mutex_lock_interruptible(&runtime->oss.params_lock)) { tmp = -ERESTARTSYS; break; } + tmp = snd_pcm_oss_make_ready_locked(substream); + if (tmp < 0) + goto err; if (bytes < runtime->oss.period_bytes || runtime->oss.buffer_used > 0) { if (runtime->oss.buffer_used == 0) { tmp = snd_pcm_oss_read2(substream, runtime->oss.buffer, runtime->oss.period_bytes, 1); @@ -1501,10 +1541,12 @@ static int snd_pcm_oss_reset(struct snd_pcm_oss_file *pcm_oss_file) continue; runtime = substream->runtime; snd_pcm_kernel_ioctl(substream, SNDRV_PCM_IOCTL_DROP, NULL); + mutex_lock(&runtime->oss.params_lock); runtime->oss.prepare = 1; runtime->oss.buffer_used = 0; runtime->oss.prev_hw_ptr_period = 0; runtime->oss.period_ptr = 0; + mutex_unlock(&runtime->oss.params_lock); } return 0; } @@ -1590,9 +1632,10 @@ static int snd_pcm_oss_sync(struct snd_pcm_oss_file *pcm_oss_file) goto __direct; if ((err = snd_pcm_oss_make_ready(substream)) < 0) return err; + if (mutex_lock_interruptible(&runtime->oss.params_lock)) + return -ERESTARTSYS; format = snd_pcm_oss_format_from(runtime->oss.format); width = snd_pcm_format_physical_width(format); - mutex_lock(&runtime->oss.params_lock); if (runtime->oss.buffer_used > 0) { #ifdef OSS_DEBUG pcm_dbg(substream->pcm, "sync: buffer_used\n"); @@ -1643,7 +1686,9 @@ static int snd_pcm_oss_sync(struct snd_pcm_oss_file *pcm_oss_file) substream->f_flags = saved_f_flags; if (err < 0) return err; + mutex_lock(&runtime->oss.params_lock); runtime->oss.prepare = 1; + mutex_unlock(&runtime->oss.params_lock); }

substream = pcm_oss_file->streams[SNDRV_PCM_STREAM_CAPTURE]; @@ -1654,8 +1699,10 @@ static int snd_pcm_oss_sync(struct snd_pcm_oss_file *pcm_oss_file) err = snd_pcm_kernel_ioctl(substream, SNDRV_PCM_IOCTL_DROP, NULL); if (err < 0) return err; + mutex_lock(&runtime->oss.params_lock); runtime->oss.buffer_used = 0; runtime->oss.prepare = 1; + mutex_unlock(&runtime->oss.params_lock); } return 0; } @@ -1674,10 +1721,13 @@ static int snd_pcm_oss_set_rate(struct snd_pcm_oss_file *pcm_oss_file, int rate) rate = 1000; else if (rate > 192000) rate = 192000; + if (mutex_lock_interruptible(&runtime->oss.params_lock)) + return -ERESTARTSYS; if (runtime->oss.rate != rate) { runtime->oss.params = 1; runtime->oss.rate = rate; } + mutex_unlock(&runtime->oss.params_lock); } return snd_pcm_oss_get_rate(pcm_oss_file); } @@ -1705,10 +1755,13 @@ static int snd_pcm_oss_set_channels(struct snd_pcm_oss_file *pcm_oss_file, unsig if (substream == NULL) continue; runtime = substream->runtime; + if (mutex_lock_interruptible(&runtime->oss.params_lock)) + return -ERESTARTSYS; if (runtime->oss.channels != channels) { runtime->oss.params = 1; runtime->oss.channels = channels; } + mutex_unlock(&runtime->oss.params_lock); } return snd_pcm_oss_get_channels(pcm_oss_file); } @@ -1794,10 +1847,13 @@ static int snd_pcm_oss_set_format(struct snd_pcm_oss_file *pcm_oss_file, int for if (substream == NULL) continue; runtime = substream->runtime; + if (mutex_lock_interruptible(&runtime->oss.params_lock)) + return -ERESTARTSYS; if (runtime->oss.format != format) { runtime->oss.params = 1; runtime->oss.format = format; } + mutex_unlock(&runtime->oss.params_lock); } } return snd_pcm_oss_get_format(pcm_oss_file); @@ -1817,8 +1873,6 @@ static int snd_pcm_oss_set_subdivide1(struct snd_pcm_substream *substream, int s { struct snd_pcm_runtime *runtime;

- if (substream == NULL) - return 0; runtime = substream->runtime; if (subdivide == 0) { subdivide = runtime->oss.subdivision; @@ -1842,9 +1896,16 @@ static int snd_pcm_oss_set_subdivide(struct snd_pcm_oss_file *pcm_oss_file, int

for (idx = 1; idx >= 0; --idx) { struct snd_pcm_substream *substream = pcm_oss_file->streams[idx]; + struct snd_pcm_runtime *runtime; + if (substream == NULL) continue; - if ((err = snd_pcm_oss_set_subdivide1(substream, subdivide)) < 0) + runtime = substream->runtime; + if (mutex_lock_interruptible(&runtime->oss.params_lock)) + return -ERESTARTSYS; + err = snd_pcm_oss_set_subdivide1(substream, subdivide); + mutex_unlock(&runtime->oss.params_lock); + if (err < 0) return err; } return err; @@ -1854,8 +1915,6 @@ static int snd_pcm_oss_set_fragment1(struct snd_pcm_substream *substream, unsign { struct snd_pcm_runtime *runtime;

- if (substream == NULL) - return 0; runtime = substream->runtime; if (runtime->oss.subdivision || runtime->oss.fragshift) return -EINVAL; @@ -1875,9 +1934,16 @@ static int snd_pcm_oss_set_fragment(struct snd_pcm_oss_file *pcm_oss_file, unsig

for (idx = 1; idx >= 0; --idx) { struct snd_pcm_substream *substream = pcm_oss_file->streams[idx]; + struct snd_pcm_runtime *runtime; + if (substream == NULL) continue; - if ((err = snd_pcm_oss_set_fragment1(substream, val)) < 0) + runtime = substream->runtime; + if (mutex_lock_interruptible(&runtime->oss.params_lock)) + return -ERESTARTSYS; + err = snd_pcm_oss_set_fragment1(substream, val); + mutex_unlock(&runtime->oss.params_lock); + if (err < 0) return err; } return err; @@ -1961,6 +2027,9 @@ static int snd_pcm_oss_set_trigger(struct snd_pcm_oss_file *pcm_oss_file, int tr } if (psubstream) { runtime = psubstream->runtime; + cmd = 0; + if (mutex_lock_interruptible(&runtime->oss.params_lock)) + return -ERESTARTSYS; if (trigger & PCM_ENABLE_OUTPUT) { if (runtime->oss.trigger) goto _skip1; @@ -1978,13 +2047,19 @@ static int snd_pcm_oss_set_trigger(struct snd_pcm_oss_file *pcm_oss_file, int tr cmd = SNDRV_PCM_IOCTL_DROP; runtime->oss.prepare = 1; } - err = snd_pcm_kernel_ioctl(psubstream, cmd, NULL); - if (err < 0) - return err; - } _skip1: + mutex_unlock(&runtime->oss.params_lock); + if (cmd) { + err = snd_pcm_kernel_ioctl(psubstream, cmd, NULL); + if (err < 0) + return err; + } + } if (csubstream) { runtime = csubstream->runtime; + cmd = 0; + if (mutex_lock_interruptible(&runtime->oss.params_lock)) + return -ERESTARTSYS; if (trigger & PCM_ENABLE_INPUT) { if (runtime->oss.trigger) goto _skip2; @@ -1999,11 +2074,14 @@ static int snd_pcm_oss_set_trigger(struct snd_pcm_oss_file *pcm_oss_file, int tr cmd = SNDRV_PCM_IOCTL_DROP; runtime->oss.prepare = 1; } - err = snd_pcm_kernel_ioctl(csubstream, cmd, NULL); - if (err < 0) - return err; - } _skip2: + mutex_unlock(&runtime->oss.params_lock); + if (cmd) { + err = snd_pcm_kernel_ioctl(csubstream, cmd, NULL); + if (err < 0) + return err; + } + } return 0; }