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Subject[PATCH 5.2 064/143] ALSA: seq: Fix potential concurrent access to the deleted pool
Date
From: Takashi Iwai <tiwai@suse.de>

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@syzkaller.appspotmail.com
Cc: <stable@vger.kernel.org>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
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
@@ -1835,8 +1835,7 @@ 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
@@ -263,3 +263,20 @@ 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
@@ -53,5 +53,7 @@ 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

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