[PATCH 4.9 60/83] ALSA: seq: Fix potential concurrent access to the deleted pool

[Greg Kroah-Hartman]

From: Takashi Iwai <tiwai@xxxxxxx>

commit 75545304eba6a3d282f923b96a466dc25a81e359 upstream.

The input pool of a client might be deleted via the resize ioctl, the
the access to it should be covered by the proper locks.  Currently the
only missing place is the call in snd_seq_ioctl_get_client_pool(), and
this patch papers over it.

Reported-by: syzbot+4a75454b9ca2777f35c7@xxxxxxxxxxxxxxxxxxxxxxxxx
Cc: <stable@xxxxxxxxxxxxxxx>
Signed-off-by: Takashi Iwai <tiwai@xxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 sound/core/seq/seq_clientmgr.c |    3 +--
 sound/core/seq/seq_fifo.c      |   17 +++++++++++++++++
 sound/core/seq/seq_fifo.h      |    2 ++
 3 files changed, 20 insertions(+), 2 deletions(-)

--- a/sound/core/seq/seq_clientmgr.c
+++ b/sound/core/seq/seq_clientmgr.c
@@ -1822,8 +1822,7 @@ static int snd_seq_ioctl_get_client_pool
 	if (cptr->type == USER_CLIENT) {
 		info->input_pool = cptr->data.user.fifo_pool_size;
 		info->input_free = info->input_pool;
-		if (cptr->data.user.fifo)
-			info->input_free = snd_seq_unused_cells(cptr->data.user.fifo->pool);
+		info->input_free = snd_seq_fifo_unused_cells(cptr->data.user.fifo);
 	} else {
 		info->input_pool = 0;
 		info->input_free = 0;
--- a/sound/core/seq/seq_fifo.c
+++ b/sound/core/seq/seq_fifo.c
@@ -278,3 +278,20 @@ int snd_seq_fifo_resize(struct snd_seq_f
 
 	return 0;
 }
+
+/* get the number of unused cells safely */
+int snd_seq_fifo_unused_cells(struct snd_seq_fifo *f)
+{
+	unsigned long flags;
+	int cells;
+
+	if (!f)
+		return 0;
+
+	snd_use_lock_use(&f->use_lock);
+	spin_lock_irqsave(&f->lock, flags);
+	cells = snd_seq_unused_cells(f->pool);
+	spin_unlock_irqrestore(&f->lock, flags);
+	snd_use_lock_free(&f->use_lock);
+	return cells;
+}
--- a/sound/core/seq/seq_fifo.h
+++ b/sound/core/seq/seq_fifo.h
@@ -68,5 +68,7 @@ int snd_seq_fifo_poll_wait(struct snd_se
 /* resize pool in fifo */
 int snd_seq_fifo_resize(struct snd_seq_fifo *f, int poolsize);
 
+/* get the number of unused cells safely */
+int snd_seq_fifo_unused_cells(struct snd_seq_fifo *f);
 
 #endif