* Re: [alsa-devel] [BUG] sound/core/seq: A possible sleep-in-atomic bug in snd_virmidi_dev_receive_event
2017-10-09 2:42 [BUG] sound/core/seq: A possible sleep-in-atomic bug in snd_virmidi_dev_receive_event Jia-Ju Bai
@ 2017-10-09 9:08 ` Takashi Iwai
0 siblings, 0 replies; 2+ messages in thread
From: Takashi Iwai @ 2017-10-09 9:08 UTC (permalink / raw)
To: Jia-Ju Bai
Cc: perex, tiwai, o-takashi, mingo, danielmentz, alsa-devel, linux-kernel
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;
--
2.14.2
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