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Commit 399ccdc1 authored Sep 25, 2008 by Takashi Iwai

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: Takashi 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)