Commit 5803b023 authored by Takashi Iwai's avatar Takashi Iwai
Browse files

ALSA: seq: Fix copy_from_user() call inside lock 



The event handler in the virmidi sequencer code takes a read-lock for
the linked list traverse, while it's calling snd_seq_dump_var_event()
in the loop.  The latter function may expand the user-space data
depending on the event type.  It eventually invokes copy_from_user(),
which might be a potential dead-lock.

The sequencer core guarantees that the user-space data is passed only
with atomic=0 argument, but snd_virmidi_dev_receive_event() ignores it
and always takes read-lock().  For avoiding the problem above, this
patch introduces rwsem for non-atomic case, while keeping rwlock for
atomic case.

Also while we're at it: the superfluous irq flags is dropped in
snd_virmidi_input_open().

Reported-by: default avatarJia-Ju Bai <baijiaju1990@163.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: default avatarTakashi Iwai <tiwai@suse.de>
parent c247487c

include/sound/seq_virmidi.h

+1 −0
Original line number Diff line number Diff line
@@ -60,6 +60,7 @@ struct snd_virmidi_dev { 
	int port;			/* created/attached port */

	unsigned int flags;		/* SNDRV_VIRMIDI_* */

	rwlock_t filelist_lock;

	struct rw_semaphore filelist_sem;

	struct list_head filelist;

};

sound/core/seq/seq_virmidi.c

+19 −8
Original line number Diff line number Diff line
@@ -77,13 +77,17 @@ static void snd_virmidi_init_event(struct snd_virmidi *vmidi, 
 * decode input event and put to read buffer of each opened file

 */

static int snd_virmidi_dev_receive_event(struct snd_virmidi_dev *rdev,

					 struct snd_seq_event *ev)

					 struct snd_seq_event *ev,

					 bool atomic)

{

	struct snd_virmidi *vmidi;

	unsigned char msg[4];

	int len;



	if (atomic)

		read_lock(&rdev->filelist_lock);

	else

		down_read(&rdev->filelist_sem);

	list_for_each_entry(vmidi, &rdev->filelist, list) {

		if (!vmidi->trigger)

			continue;
@@ -97,7 +101,10 @@ static int snd_virmidi_dev_receive_event(struct snd_virmidi_dev *rdev, 
				snd_rawmidi_receive(vmidi->substream, msg, len);

		}

	}

	if (atomic)

		read_unlock(&rdev->filelist_lock);

	else

		up_read(&rdev->filelist_sem);



	return 0;

}
@@ -115,7 +122,7 @@ int snd_virmidi_receive(struct snd_rawmidi *rmidi, struct snd_seq_event *ev) 
	struct snd_virmidi_dev *rdev;



	rdev = rmidi->private_data;

	return snd_virmidi_dev_receive_event(rdev, ev);

	return snd_virmidi_dev_receive_event(rdev, ev, true);

}

#endif  /*  0  */
@@ -130,7 +137,7 @@ static int snd_virmidi_event_input(struct snd_seq_event *ev, int direct, 
	rdev = private_data;

	if (!(rdev->flags & SNDRV_VIRMIDI_USE))

		return 0; /* ignored */

	return snd_virmidi_dev_receive_event(rdev, ev);

	return snd_virmidi_dev_receive_event(rdev, ev, atomic);

}



/*
@@ -209,7 +216,6 @@ static int snd_virmidi_input_open(struct snd_rawmidi_substream *substream) 
	struct snd_virmidi_dev *rdev = substream->rmidi->private_data;

	struct snd_rawmidi_runtime *runtime = substream->runtime;

	struct snd_virmidi *vmidi;

	unsigned long flags;



	vmidi = kzalloc(sizeof(*vmidi), GFP_KERNEL);

	if (vmidi == NULL)
@@ -223,9 +229,11 @@ static int snd_virmidi_input_open(struct snd_rawmidi_substream *substream) 
	vmidi->client = rdev->client;

	vmidi->port = rdev->port;	

	runtime->private_data = vmidi;

	write_lock_irqsave(&rdev->filelist_lock, flags);

	down_write(&rdev->filelist_sem);

	write_lock_irq(&rdev->filelist_lock);

	list_add_tail(&vmidi->list, &rdev->filelist);

	write_unlock_irqrestore(&rdev->filelist_lock, flags);

	write_unlock_irq(&rdev->filelist_lock);

	up_write(&rdev->filelist_sem);

	vmidi->rdev = rdev;

	return 0;

}
@@ -264,9 +272,11 @@ static int snd_virmidi_input_close(struct snd_rawmidi_substream *substream) 
	struct snd_virmidi_dev *rdev = substream->rmidi->private_data;

	struct snd_virmidi *vmidi = substream->runtime->private_data;



	down_write(&rdev->filelist_sem);

	write_lock_irq(&rdev->filelist_lock);

	list_del(&vmidi->list);

	write_unlock_irq(&rdev->filelist_lock);

	up_write(&rdev->filelist_sem);

	snd_midi_event_free(vmidi->parser);

	substream->runtime->private_data = NULL;

	kfree(vmidi);
@@ -520,6 +530,7 @@ int snd_virmidi_new(struct snd_card *card, int device, struct snd_rawmidi **rrmi 
	rdev->rmidi = rmidi;

	rdev->device = device;

	rdev->client = -1;

	init_rwsem(&rdev->filelist_sem);

	rwlock_init(&rdev->filelist_lock);

	INIT_LIST_HEAD(&rdev->filelist);

	rdev->seq_mode = SNDRV_VIRMIDI_SEQ_DISPATCH;

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