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From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org,
        syzbot+4a75454b9ca2777f35c7@syzkaller.appspotmail.com,
        Takashi Iwai <tiwai@suse.de>
Subject: [PATCH 5.2 064/143] ALSA: seq: Fix potential concurrent access to the deleted pool
Date:   Wed,  4 Sep 2019 19:53:27 +0200
Message-Id: <20190904175316.576668488@linuxfoundation.org>
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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