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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: Jia-Ju Bai <baijiaju1990@163.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
This commit is contained in:
Takashi Iwai 2017-10-09 10:02:56 +02:00
parent c247487c0d
commit 5803b02388
2 changed files with 20 additions and 8 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

1
include/sound/seq_virmidi.h
View File

@ -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;
};

27
sound/core/seq/seq_virmidi.c
View File

@ -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;
read_lock(&rdev->filelist_lock);
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);
}
}
read_unlock(&rdev->filelist_lock);
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;