[PATCH 6.4 522/800] ALSA: pcm: Fix potential data race at PCM memory allocation helpers

Greg Kroah-Hartman
2023-07-16T20:17:21Z

From: Takashi Iwai <tiwai@suse.de>

commit bd55842ed998a622ba6611fe59b3358c9f76773d upstream.

The PCM memory allocation helpers have a sanity check against too many
buffer allocations. However, the check is performed without a proper
lock and the allocation isn't serialized; this allows user to allocate
more memories than predefined max size.

Practically seen, this isn't really a big problem, as it's more or
less some "soft limit" as a sanity check, and it's not possible to
allocate unlimitedly. But it's still better to address this for more
consistent behavior.

The patch covers the size check in do_alloc_pages() with the
card->memory_mutex, and increases the allocated size there for
preventing the further overflow. When the actual allocation fails,
the size is decreased accordingly.

Reported-by: BassCheck <bass@buaa.edu.cn>
Reported-by: Tuo Li <islituo@gmail.com>
Link: https://lore.kernel.org/r/CADm8Tek6t0WedK+3Y6rbE5YEt19tML8BUL45N2ji4ZAz1KcN_A@mail.gmail.com
Reviewed-by: Jaroslav Kysela <perex@perex.cz>
Cc: <stable@vger.kernel.org>
Link: https://lore.kernel.org/r/20230703112430.30634-1-tiwai@suse.de
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
sound/core/pcm_memory.c | 44 ++++++++++++++++++++++++++++++++++++--------
1 file changed, 36 insertions(+), 8 deletions(-)

--- a/sound/core/pcm_memory.c
+++ b/sound/core/pcm_memory.c
@@ -31,15 +31,41 @@ static unsigned long max_alloc_per_card
module_param(max_alloc_per_card, ulong, 0644);
MODULE_PARM_DESC(max_alloc_per_card, "Max total allocation bytes per card.");

+static void __update_allocated_size(struct snd_card *card, ssize_t bytes)
+{
+ card->total_pcm_alloc_bytes += bytes;
+}
+
+static void update_allocated_size(struct snd_card *card, ssize_t bytes)
+{
+ mutex_lock(&card->memory_mutex);
+ __update_allocated_size(card, bytes);
+ mutex_unlock(&card->memory_mutex);
+}
+
+static void decrease_allocated_size(struct snd_card *card, size_t bytes)
+{
+ mutex_lock(&card->memory_mutex);
+ WARN_ON(card->total_pcm_alloc_bytes < bytes);
+ __update_allocated_size(card, -(ssize_t)bytes);
+ mutex_unlock(&card->memory_mutex);
+}
+
static int do_alloc_pages(struct snd_card *card, int type, struct device *dev,
int str, size_t size, struct snd_dma_buffer *dmab)
{
enum dma_data_direction dir;
int err;

+ /* check and reserve the requested size */
+ mutex_lock(&card->memory_mutex);
if (max_alloc_per_card &&
- card->total_pcm_alloc_bytes + size > max_alloc_per_card)
+ card->total_pcm_alloc_bytes + size > max_alloc_per_card) {
+ mutex_unlock(&card->memory_mutex);
return -ENOMEM;
+ }
+ __update_allocated_size(card, size);
+ mutex_unlock(&card->memory_mutex);

if (str == SNDRV_PCM_STREAM_PLAYBACK)
dir = DMA_TO_DEVICE;
@@ -47,9 +73,14 @@ static int do_alloc_pages(struct snd_car
dir = DMA_FROM_DEVICE;
err = snd_dma_alloc_dir_pages(type, dev, dir, size, dmab);
if (!err) {
- mutex_lock(&card->memory_mutex);
- card->total_pcm_alloc_bytes += dmab->bytes;
- mutex_unlock(&card->memory_mutex);
+ /* the actual allocation size might be bigger than requested,
+ * and we need to correct the account
+ */
+ if (dmab->bytes != size)
+ update_allocated_size(card, dmab->bytes - size);
+ } else {
+ /* take back on allocation failure */
+ decrease_allocated_size(card, size);
}
return err;
}
@@ -58,10 +89,7 @@ static void do_free_pages(struct snd_car
{
if (!dmab->area)
return;
- mutex_lock(&card->memory_mutex);
- WARN_ON(card->total_pcm_alloc_bytes < dmab->bytes);
- card->total_pcm_alloc_bytes -= dmab->bytes;
- mutex_unlock(&card->memory_mutex);
+ decrease_allocated_size(card, dmab->bytes);
snd_dma_free_pages(dmab);
dmab->area = NULL;
}