Commit 69534c48 authored by Takashi Iwai's avatar Takashi Iwai
Browse files

ALSA: pcm: Fix races among concurrent prealloc proc writes 



We have no protection against concurrent PCM buffer preallocation
changes via proc files, and it may potentially lead to UAF or some
weird problem.  This patch applies the PCM open_mutex to the proc
write operation for avoiding the racy proc writes and the PCM stream
open (and further operations).

Cc: <stable@vger.kernel.org>
Reviewed-by: default avatarJaroslav Kysela <perex@perex.cz>
Link: https://lore.kernel.org/r/20220322170720.3529-5-tiwai@suse.de


Signed-off-by: default avatarTakashi Iwai <tiwai@suse.de>
parent 3c3201f8

sound/core/pcm_memory.c

+7 −4
Original line number Diff line number Diff line
@@ -163,19 +163,20 @@ static void snd_pcm_lib_preallocate_proc_write(struct snd_info_entry *entry, 
	size_t size;

	struct snd_dma_buffer new_dmab;



	mutex_lock(&substream->pcm->open_mutex);

	if (substream->runtime) {

		buffer->error = -EBUSY;

		return;

		goto unlock;

	}

	if (!snd_info_get_line(buffer, line, sizeof(line))) {

		snd_info_get_str(str, line, sizeof(str));

		size = simple_strtoul(str, NULL, 10) * 1024;

		if ((size != 0 && size < 8192) || size > substream->dma_max) {

			buffer->error = -EINVAL;

			return;

			goto unlock;

		}

		if (substream->dma_buffer.bytes == size)

			return;

			goto unlock;

		memset(&new_dmab, 0, sizeof(new_dmab));

		new_dmab.dev = substream->dma_buffer.dev;

		if (size > 0) {
@@ -189,7 +190,7 @@ static void snd_pcm_lib_preallocate_proc_write(struct snd_info_entry *entry, 
					 substream->pcm->card->number, substream->pcm->device,

					 substream->stream ? 'c' : 'p', substream->number,

					 substream->pcm->name, size);

				return;

				goto unlock;

			}

			substream->buffer_bytes_max = size;

		} else {
@@ -201,6 +202,8 @@ static void snd_pcm_lib_preallocate_proc_write(struct snd_info_entry *entry, 
	} else {

		buffer->error = -EINVAL;

	}

 unlock:

	mutex_unlock(&substream->pcm->open_mutex);

}



static inline void preallocate_info_init(struct snd_pcm_substream *substream)