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>
diff --git a/sound/core/pcm.c b/sound/core/pcm.c
index 9dd9bc7..ece25c7 100644
--- a/sound/core/pcm.c
+++ b/sound/core/pcm.c
@@ -781,7 +781,7 @@
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 @@
break;
}
}
- up_read(&card->controls_rwsem);
+ read_unlock(&card->ctl_files_rwlock);
switch (stream) {
case SNDRV_PCM_STREAM_PLAYBACK: