ALSA: rawmidi: fix oops (use after free) when unloading a driver module

When a driver module is unloaded and the last still open file is a raw
MIDI device, the card and its devices will be actually freed in the
snd_card_file_remove() call when that file is closed.  Afterwards, rmidi
and rmidi->card point into freed memory, so the module pointer is likely
to be garbage.
(This was introduced by commit 9a1b64ca.)
Signed-off-by: Clemens Ladisch <clemens@ladisch.de>
Reported-by: Krzysztof Foltman <wdev@foltman.com>
Cc: 2.6.30-2.6.35 <stable@kernel.org>
Signed-off-by: Takashi Iwai <tiwai@suse.de>

sound/core/rawmidi.c

@@ -535,13 +535,15 @@ static int snd_rawmidi_release(struct inode *inode, struct file *file)
 {
 	struct snd_rawmidi_file *rfile;
 	struct snd_rawmidi *rmidi;
+	struct module *module;
 
 	rfile = file->private_data;
 	rmidi = rfile->rmidi;
 	rawmidi_release_priv(rfile);
 	kfree(rfile);
+	module = rmidi->card->module;
 	snd_card_file_remove(rmidi->card, file);
-	module_put(rmidi->card->module);
+	module_put(module);
 	return 0;
 }