media: vb2: vb2_mmap: move lock up

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>

diff --git a/drivers/media/v4l2-core/videobuf2-core.c b/drivers/media/v4l2-core/videobuf2-core.c
index 4df4a1f402bed57d831f6846fed54ab04ee5c5eb..fa970650e913b88d8ea165eebe79678296cecbd0 100644 (file)
--- a/drivers/media/v4l2-core/videobuf2-core.c
+++ b/drivers/media/v4l2-core/videobuf2-core.c
@@ -1916,9 +1916,13 @@ 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;
        }
 
        /*
@@ -1926,7 +1930,7 @@ 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];
 
@@ -1942,8 +1946,9 @@ 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;