This is a note to let you know that I've just added the patch titled
ALSA: pcm: Fix potential data race at PCM memory allocation helpers
to the 5.4-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
alsa-pcm-fix-potential-data-race-at-pcm-memory-alloc.patch
and it can be found in the queue-5.4 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
commit 1e1e845af20e7af462dac1f6ca891de24b59c6d8
Author: Takashi Iwai <tiwai@xxxxxxx>
Date: Mon Jul 3 13:24:30 2023 +0200
ALSA: pcm: Fix potential data race at PCM memory allocation helpers
[ Upstream commit bd55842ed998a622ba6611fe59b3358c9f76773d ]
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@xxxxxxxxxxx>
Reported-by: Tuo Li <islituo@xxxxxxxxx>
Link: https://lore.kernel.org/r/CADm8Tek6t0WedK+3Y6rbE5YEt19tML8BUL45N2ji4ZAz1KcN_A@xxxxxxxxxxxxxx
Reviewed-by: Jaroslav Kysela <perex@xxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>
Link: https://lore.kernel.org/r/20230703112430.30634-1-tiwai@xxxxxxx
Signed-off-by: Takashi Iwai <tiwai@xxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
diff --git a/sound/core/pcm_memory.c b/sound/core/pcm_memory.c
index 97b471d7b32e5..beca39f7c8f35 100644
--- a/sound/core/pcm_memory.c
+++ b/sound/core/pcm_memory.c
@@ -31,14 +31,40 @@ static unsigned long max_alloc_per_card = 32UL * 1024UL * 1024UL;
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,
size_t size, struct snd_dma_buffer *dmab)
{
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 (IS_ENABLED(CONFIG_SND_DMA_SGBUF) &&
(type == SNDRV_DMA_TYPE_DEV_SG || type == SNDRV_DMA_TYPE_DEV_UC_SG) &&
@@ -53,9 +79,14 @@ static int do_alloc_pages(struct snd_card *card, int type, struct device *dev,
err = snd_dma_alloc_pages(type, dev, 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;
}
@@ -64,10 +95,7 @@ static void do_free_pages(struct snd_card *card, struct snd_dma_buffer *dmab)
{
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;
}
