Commit cd26d1c4 authored Nov 13, 2018 by Hans Verkuil Committed by Mauro Carvalho Chehab Nov 23, 2018

media: vb2: vb2_mmap: move lock up



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>

parent 2e84eb9a

drivers/media/common/videobuf2/videobuf2-core.c

+8 −3

Original line number	Diff line number	Diff line
		@@ -2117,9 +2117,13 @@ int vb2_mmap(struct vb2_queue q, struct vm_area_struct vma)
		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;
		}

		/*
		@@ -2127,7 +2131,7 @@ int vb2_mmap(struct vb2_queue q, struct vm_area_struct vma)
		*/
		ret = __find_plane_by_offset(q, off, &buffer, &plane);
		if (ret)
		return ret;
		goto unlock;

		vb = q->bufs[buffer];

		@@ -2143,8 +2147,9 @@ int vb2_mmap(struct vb2_queue q, struct vm_area_struct vma)
		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;

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