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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, Hans Verkuil <hverkuil@xs4all.nl>,
        syzbot+be93025dd45dccd8923c@syzkaller.appspotmail.com,
        Hans Verkuil <hansverk@cisco.com>,
        Mauro Carvalho Chehab <mchehab+samsung@kernel.org>
Subject: [PATCH 4.4 058/104] media: vb2: vb2_mmap: move lock up
Date:   Thu, 24 Jan 2019 20:19:47 +0100
Message-Id: <20190124190202.104335919@linuxfoundation.org>
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4.4-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Hans Verkuil <hverkuil@xs4all.nl>

commit cd26d1c4d1bc947b56ae404998ae2276df7b39b7 upstream.

If a filehandle is dup()ped, then it is possible to close it from one fd
and call mmap from the other. This creates a race condition in vb2_mmap
where it is using queue data that __vb2_queue_free (called from close())
is in the process of releasing.

By moving up the mutex_lock(mmap_lock) in vb2_mmap this race is avoided
since __vb2_queue_free is called with the same mutex locked. So vb2_mmap
now reads consistent buffer data.

Signed-off-by: Hans Verkuil <hverkuil@xs4all.nl>
Reported-by: syzbot+be93025dd45dccd8923c@syzkaller.appspotmail.com
Signed-off-by: Hans Verkuil <hansverk@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 drivers/media/v4l2-core/videobuf2-core.c |   11 ++++++++---
 1 file changed, 8 insertions(+), 3 deletions(-)

--- a/drivers/media/v4l2-core/videobuf2-core.c
+++ b/drivers/media/v4l2-core/videobuf2-core.c
@@ -1976,9 +1976,13 @@ int vb2_mmap(struct vb2_queue *q, struct
 			return -EINVAL;
 		}
 	}
+
+	mutex_lock(&q->mmap_lock);
+
 	if (vb2_fileio_is_active(q)) {
 		dprintk(1, "mmap: file io in progress\n");
-		return -EBUSY;
+		ret = -EBUSY;
+		goto unlock;
 	}
 
 	/*
@@ -1986,7 +1990,7 @@ int vb2_mmap(struct vb2_queue *q, struct
 	 */
 	ret = __find_plane_by_offset(q, off, &buffer, &plane);
 	if (ret)
-		return ret;
+		goto unlock;
 
 	vb = q->bufs[buffer];
 
@@ -2002,8 +2006,9 @@ int vb2_mmap(struct vb2_queue *q, struct
 		return -EINVAL;
 	}
 
-	mutex_lock(&q->mmap_lock);
 	ret = call_memop(vb, mmap, vb->planes[plane].mem_priv, vma);
+
+unlock:
 	mutex_unlock(&q->mmap_lock);
 	if (ret)
 		return ret;