ALSA: fix locking in snd_pcm_open*() and snd_rawmidi_open*()
Takashi Iwai [Thu, 25 Sep 2008 12:51:03 +0000 (14:51 +0200)]
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>

sound/core/pcm.c
sound/core/rawmidi.c

index 9dd9bc7..ece25c7 100644 (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:
index f7ea728..b917a9f 100644 (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)