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_... Reviewed-by: Jaroslav Kysela perex@perex.cz Cc: stable@vger.kernel.org Signed-off-by: Takashi Iwai tiwai@suse.de --- sound/core/pcm_memory.c | 44 +++++++++++++++++++++++++++++++++-------- 1 file changed, 36 insertions(+), 8 deletions(-)

diff --git a/sound/core/pcm_memory.c b/sound/core/pcm_memory.c index 7bde7fb64011..a0b951471699 100644 --- a/sound/core/pcm_memory.c +++ b/sound/core/pcm_memory.c @@ -31,15 +31,41 @@ 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, 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_card *card, int type, struct device *dev, 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_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; }