On Mon, 09 Oct 2017 04:42:15 +0200, Jia-Ju Bai wrote:

According to seq_virmidi.c, the driver may sleep under a read spinlock. The function call path is: snd_virmidi_dev_receive_event (acquire the spinlock) snd_seq_dump_var_event copy_from_user --> may sleep

This bug is found by my static analysis tool and my code review.

OK, this looks like a real bug. The fixed patch is below.

thanks,

Takashi

-- 8< -- From: Takashi Iwai tiwai@suse.de Subject: [PATCH] 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 --- include/sound/seq_virmidi.h | 1 + sound/core/seq/seq_virmidi.c | 27 +++++++++++++++++++-------- 2 files changed, 20 insertions(+), 8 deletions(-)

diff --git a/include/sound/seq_virmidi.h b/include/sound/seq_virmidi.h index a03acd0d398a..695257ae64ac 100644 --- 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 8d93a4021c78..f48a4cd24ffc 100644 --- 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;