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linux-sg2042
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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>
This commit is contained in:
Takashi Iwai 2008-09-25 14:51:03 +02:00
parent b0b8daf784
commit 399ccdc1cd
2 changed files with 4 additions and 4 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

4
sound/core/pcm.c
View File

@ -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:

4
sound/core/rawmidi.c
View File

@ -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)