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Commit 3a381abc authored by Jens Axboe's avatar Jens Axboe Committed by Greg Kroah-Hartman
Browse files

nbd: fix use-after-free of rq/bio in the xmit path 



commit 429a787be6793554ee02aacc7e1f11ebcecc4453 upstream.

For writes, we can get a completion in while we're still iterating
the request and bio chain. If that happens, we're reading freed
memory and we can crash.

Break out after the last segment and avoid having the iterator
read freed memory.

Reviewed-by: default avatarJosef Bacik <jbacik@fb.com>
Signed-off-by: default avatarJens Axboe <axboe@fb.com>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent 2b9b2002

drivers/block/nbd.c

+23 −9
Original line number Diff line number Diff line
@@ -272,6 +272,7 @@ static int nbd_send_cmd(struct nbd_device *nbd, struct nbd_cmd *cmd) 
	int result, flags;

	struct nbd_request request;

	unsigned long size = blk_rq_bytes(req);

	struct bio *bio;

	u32 type;



	if (req->cmd_type == REQ_TYPE_DRV_PRIV)
@@ -305,16 +306,20 @@ static int nbd_send_cmd(struct nbd_device *nbd, struct nbd_cmd *cmd) 
		return -EIO;

	}



	if (type == NBD_CMD_WRITE) {

		struct req_iterator iter;

		struct bio_vec bvec;

		/*

		 * we are really probing at internals to determine

		 * whether to set MSG_MORE or not...

		 */

		rq_for_each_segment(bvec, req, iter) {

	if (type != NBD_CMD_WRITE)

		return 0;



	flags = 0;

			if (!rq_iter_last(bvec, iter))

	bio = req->bio;

	while (bio) {

		struct bio *next = bio->bi_next;

		struct bvec_iter iter;

		struct bio_vec bvec;



		bio_for_each_segment(bvec, bio, iter) {

			bool is_last = !next && bio_iter_last(bvec, iter);



			if (is_last)

				flags = MSG_MORE;

			dev_dbg(nbd_to_dev(nbd), "request %p: sending %d bytes data\n",

				cmd, bvec.bv_len);
@@ -325,7 +330,16 @@ static int nbd_send_cmd(struct nbd_device *nbd, struct nbd_cmd *cmd) 
					result);

				return -EIO;

			}

			/*

			 * The completion might already have come in,

			 * so break for the last one instead of letting

			 * the iterator do it. This prevents use-after-free

			 * of the bio.

			 */

			if (is_last)

				break;

		}

		bio = next;

	}

	return 0;

}