[PATCH 5.17 11/39] ALSA: pcm: Fix races among concurrent hw_params and hw_free calls

Greg Kroah-Hartman
2022-03-25T15:28:15Z

From: Takashi Iwai <tiwai@suse.de>

commit 92ee3c60ec9fe64404dc035e7c41277d74aa26cb upstream.

Currently we have neither proper check nor protection against the
concurrent calls of PCM hw_params and hw_free ioctls, which may result
in a UAF. Since the existing PCM stream lock can't be used for
protecting the whole ioctl operations, we need a new mutex to protect
those racy calls.

This patch introduced a new mutex, runtime->buffer_mutex, and applies
it to both hw_params and hw_free ioctl code paths. Along with it, the
both functions are slightly modified (the mmap_count check is moved
into the state-check block) for code simplicity.

Reported-by: Hu Jiahui <kirin.say@gmail.com>
Cc: <stable@vger.kernel.org>
Reviewed-by: Jaroslav Kysela <perex@perex.cz>
Link: https://lore.kernel.org/r/20220322170720.3529-2-tiwai@suse.de
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
include/sound/pcm.h | 1
sound/core/pcm.c | 2 +
sound/core/pcm_native.c | 61 ++++++++++++++++++++++++++++++------------------
3 files changed, 42 insertions(+), 22 deletions(-)

--- a/include/sound/pcm.h
+++ b/include/sound/pcm.h
@@ -401,6 +401,7 @@ struct snd_pcm_runtime {
wait_queue_head_t tsleep; /* transfer sleep */
struct fasync_struct *fasync;
bool stop_operating; /* sync_stop will be called */
+ struct mutex buffer_mutex; /* protect for buffer changes */

/* -- private section -- */
void *private_data;
--- a/sound/core/pcm.c
+++ b/sound/core/pcm.c
@@ -969,6 +969,7 @@ int snd_pcm_attach_substream(struct snd_
init_waitqueue_head(&runtime->tsleep);

runtime->status->state = SNDRV_PCM_STATE_OPEN;
+ mutex_init(&runtime->buffer_mutex);

substream->runtime = runtime;
substream->private_data = pcm->private_data;
@@ -1002,6 +1003,7 @@ void snd_pcm_detach_substream(struct snd
} else {
substream->runtime = NULL;
}
+ mutex_destroy(&runtime->buffer_mutex);
kfree(runtime);
put_pid(substream->pid);
substream->pid = NULL;
--- a/sound/core/pcm_native.c
+++ b/sound/core/pcm_native.c
@@ -685,33 +685,40 @@ static int snd_pcm_hw_params_choose(stru
return 0;
}

+#if IS_ENABLED(CONFIG_SND_PCM_OSS)
+#define is_oss_stream(substream) ((substream)->oss.oss)
+#else
+#define is_oss_stream(substream) false
+#endif
+
static int snd_pcm_hw_params(struct snd_pcm_substream *substream,
struct snd_pcm_hw_params *params)
{
struct snd_pcm_runtime *runtime;
- int err, usecs;
+ int err = 0, usecs;
unsigned int bits;
snd_pcm_uframes_t frames;

if (PCM_RUNTIME_CHECK(substream))
return -ENXIO;
runtime = substream->runtime;
+ mutex_lock(&runtime->buffer_mutex);
snd_pcm_stream_lock_irq(substream);
switch (runtime->status->state) {
case SNDRV_PCM_STATE_OPEN:
case SNDRV_PCM_STATE_SETUP:
case SNDRV_PCM_STATE_PREPARED:
+ if (!is_oss_stream(substream) &&
+ atomic_read(&substream->mmap_count))
+ err = -EBADFD;
break;
default:
- snd_pcm_stream_unlock_irq(substream);
- return -EBADFD;
+ err = -EBADFD;
+ break;
}
snd_pcm_stream_unlock_irq(substream);
-#if IS_ENABLED(CONFIG_SND_PCM_OSS)
- if (!substream->oss.oss)
-#endif
- if (atomic_read(&substream->mmap_count))
- return -EBADFD;
+ if (err)
+ goto unlock;

snd_pcm_sync_stop(substream, true);

@@ -799,16 +806,21 @@ static int snd_pcm_hw_params(struct snd_
if (usecs >= 0)
cpu_latency_qos_add_request(&substream->latency_pm_qos_req,
usecs);
- return 0;
+ err = 0;
_error:
- /* hardware might be unusable from this time,
- so we force application to retry to set
- the correct hardware parameter settings */
- snd_pcm_set_state(substream, SNDRV_PCM_STATE_OPEN);
- if (substream->ops->hw_free != NULL)
- substream->ops->hw_free(substream);
- if (substream->managed_buffer_alloc)
- snd_pcm_lib_free_pages(substream);
+ if (err) {
+ /* hardware might be unusable from this time,
+ * so we force application to retry to set
+ * the correct hardware parameter settings
+ */
+ snd_pcm_set_state(substream, SNDRV_PCM_STATE_OPEN);
+ if (substream->ops->hw_free != NULL)
+ substream->ops->hw_free(substream);
+ if (substream->managed_buffer_alloc)
+ snd_pcm_lib_free_pages(substream);
+ }
+ unlock:
+ mutex_unlock(&runtime->buffer_mutex);
return err;
}

@@ -848,26 +860,31 @@ static int do_hw_free(struct snd_pcm_sub
static int snd_pcm_hw_free(struct snd_pcm_substream *substream)
{
struct snd_pcm_runtime *runtime;
- int result;
+ int result = 0;

if (PCM_RUNTIME_CHECK(substream))
return -ENXIO;
runtime = substream->runtime;
+ mutex_lock(&runtime->buffer_mutex);
snd_pcm_stream_lock_irq(substream);
switch (runtime->status->state) {
case SNDRV_PCM_STATE_SETUP:
case SNDRV_PCM_STATE_PREPARED:
+ if (atomic_read(&substream->mmap_count))
+ result = -EBADFD;
break;
default:
- snd_pcm_stream_unlock_irq(substream);
- return -EBADFD;
+ result = -EBADFD;
+ break;
}
snd_pcm_stream_unlock_irq(substream);
- if (atomic_read(&substream->mmap_count))
- return -EBADFD;
+ if (result)
+ goto unlock;
result = do_hw_free(substream);
snd_pcm_set_state(substream, SNDRV_PCM_STATE_OPEN);
cpu_latency_qos_remove_request(&substream->latency_pm_qos_req);
+ unlock:
+ mutex_unlock(&runtime->buffer_mutex);
return result;
}