From: Takashi Iwai <tiwai@suse.de>
Date: Thu, 25 Sep 2008 12:51:03 +0000 (+0200)
Subject: ALSA: fix locking in snd_pcm_open*() and snd_rawmidi_open*()
X-Git-Tag: v2.6.27-rc8~14^2~1
X-Git-Url: http://pilppa.com/gitweb/?a=commitdiff_plain;h=399ccdc1cd4e92e541d4dacbbf18c52bd693418b;p=linux-2.6-omap-h63xx.git

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 9dd9bc73fe1..ece25c718e9 100644
--- a/sound/core/pcm.c
+++ b/sound/core/pcm.c
@@ -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:
diff --git a/sound/core/rawmidi.c b/sound/core/rawmidi.c
index f7ea7287c59..b917a9f981c 100644
--- a/sound/core/rawmidi.c
+++ b/sound/core/rawmidi.c
@@ -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)