autofs4: fix waitq locking

The autofs4_catatonic_mode() function accesses the wait queue without any
locking but can be called at any time.  This could lead to a possible
double free of the name field of the wait and a double fput of the daemon
communication pipe or an fput of a NULL file pointer.
Signed-off-by: Ian Kent <raven@themaw.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

fs/autofs4/inode.c

@@ -163,8 +163,8 @@ void autofs4_kill_sb(struct super_block *sb)
 	if (!sbi)
 		goto out_kill_sb;
 
-	if (!sbi->catatonic)
-		autofs4_catatonic_mode(sbi); /* Free wait queues, close pipe */
+	/* Free wait queues, close pipe */
+	autofs4_catatonic_mode(sbi);
 
 	/* Clean up and release dangling references */
 	autofs4_force_release(sbi);

fs/autofs4/waitq.c

@@ -28,6 +28,12 @@ void autofs4_catatonic_mode(struct autofs_sb_info *sbi)
 {
 	struct autofs_wait_queue *wq, *nwq;
 
+	mutex_lock(&sbi->wq_mutex);
+	if (sbi->catatonic) {
+		mutex_unlock(&sbi->wq_mutex);
+		return;
+	}
+
 	DPRINTK("entering catatonic mode");
 
 	sbi->catatonic = 1;
@@ -45,6 +51,8 @@ void autofs4_catatonic_mode(struct autofs_sb_info *sbi)
 	}
 	fput(sbi->pipe);	/* Close the pipe */
 	sbi->pipe = NULL;
+	sbi->pipefd = -1;
+	mutex_unlock(&sbi->wq_mutex);
 }
 
 static int autofs4_write(struct file *file, const void *addr, int bytes)
@@ -333,17 +341,10 @@ int autofs4_wait(struct autofs_sb_info *sbi, struct dentry *dentry,
 			wq->name.name, notify);
 	}
 
-	/* wq->name is NULL if and only if the lock is already released */
-
-	if (sbi->catatonic) {
-		/* We might have slept, so check again for catatonic mode */
-		wq->status = -ENOENT;
-		if (wq->name.name) {
-			kfree(wq->name.name);
-			wq->name.name = NULL;
-		}
-	}
-
+	/*
+	 * wq->name.name is NULL iff the lock is already released
+	 * or the mount has been made catatonic.
+	 */
 	if (wq->name.name) {
 		/* Block all but "shutdown" signals while waiting */
 		sigset_t oldset;