Commit 399ccdc1 authored by Takashi Iwai's avatar Takashi Iwai
Browse files

ALSA: fix locking in snd_pcm_open*() and snd_rawmidi_open*() 



The PCM and rawmidi open callbacks have a lock against card->controls_list
but it takes a wrong one, card->controls_rwsem, instead of a right one
card->ctl_files_rwlock.  This patch fixes them.

This change also fixes automatically the potential deadlocks due to
mm->mmap_sem in munmap and copy_from/to_user, reported by Sitsofe
Wheeler:

  A: snd_ctl_elem_user_tlv(): card->controls_rwsem => mm->mmap_sem
  B: snd_pcm_open(): card->open_mutex => card->controls_rwsem
  C: munmap: mm->mmap_sem => snd_pcm_release(): card->open_mutex

The patch breaks the chain.

Signed-off-by: default avatarTakashi Iwai <tiwai@suse.de>
parent b0b8daf7

sound/core/pcm.c

+2 −2
Original line number Diff line number Diff line
@@ -781,7 +781,7 @@ int snd_pcm_attach_substream(struct snd_pcm *pcm, int stream, 
		return -ENODEV;



	card = pcm->card;

	down_read(&card->controls_rwsem);

	read_lock(&card->ctl_files_rwlock);

	list_for_each_entry(kctl, &card->ctl_files, list) {

		if (kctl->pid == current->pid) {

			prefer_subdevice = kctl->prefer_pcm_subdevice;
@@ -789,7 +789,7 @@ int snd_pcm_attach_substream(struct snd_pcm *pcm, int stream, 
				break;

		}

	}

	up_read(&card->controls_rwsem);

	read_unlock(&card->ctl_files_rwlock);



	switch (stream) {

	case SNDRV_PCM_STREAM_PLAYBACK:

sound/core/rawmidi.c

+2 −2
Original line number Diff line number Diff line
@@ -418,7 +418,7 @@ static int snd_rawmidi_open(struct inode *inode, struct file *file) 
	mutex_lock(&rmidi->open_mutex);

	while (1) {

		subdevice = -1;

		down_read(&card->controls_rwsem);

		read_lock(&card->ctl_files_rwlock);

		list_for_each_entry(kctl, &card->ctl_files, list) {

			if (kctl->pid == current->pid) {

				subdevice = kctl->prefer_rawmidi_subdevice;
@@ -426,7 +426,7 @@ static int snd_rawmidi_open(struct inode *inode, struct file *file) 
					break;

			}

		}

		up_read(&card->controls_rwsem);

		read_unlock(&card->ctl_files_rwlock);

		err = snd_rawmidi_kernel_open(rmidi->card, rmidi->device,

					      subdevice, fflags, rawmidi_file);

		if (err >= 0)

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