ALSA: seq: Fix copy_from_user() call inside lock

commit 5803b023881857db32ffefa0d269c90280a67ee0 upstream.

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>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

diff --git a/include/sound/seq_virmidi.h b/include/sound/seq_virmidi.h
index d888433..ecfd526 100644 (file)
--- a/include/sound/seq_virmidi.h
+++ b/include/sound/seq_virmidi.h
@@ -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;
 };
 

diff --git a/sound/core/seq/seq_virmidi.c b/sound/core/seq/seq_virmidi.c
index 6b38e7c..c90464d 100644 (file)
--- a/sound/core/seq/seq_virmidi.c
+++ b/sound/core/seq/seq_virmidi.c
@@ -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;