This is a note to let you know that I've just added the patch titled

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

to the 4.9-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git%3Ba=su...

The filename of the patch is: nbd-fix-use-after-free-of-rq-bio-in-the-xmit-path.patch and it can be found in the queue-4.9 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let stable@vger.kernel.org know about it.

From 429a787be6793554ee02aacc7e1f11ebcecc4453 Mon Sep 17 00:00:00 2001

From: Jens Axboe axboe@fb.com Date: Thu, 17 Nov 2016 12:30:37 -0700 Subject: nbd: fix use-after-free of rq/bio in the xmit path

From: Jens Axboe axboe@fb.com

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: Josef Bacik jbacik@fb.com Signed-off-by: Jens Axboe axboe@fb.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org

--- drivers/block/nbd.c | 32 +++++++++++++++++++++++--------- 1 file changed, 23 insertions(+), 9 deletions(-)

--- a/drivers/block/nbd.c +++ b/drivers/block/nbd.c @@ -272,6 +272,7 @@ static int nbd_send_cmd(struct nbd_devic 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_devic return -EIO; }

- if (type == NBD_CMD_WRITE) { - struct req_iterator iter; + if (type != NBD_CMD_WRITE) + return 0; + + flags = 0; + bio = req->bio; + while (bio) { + struct bio *next = bio->bi_next; + struct bvec_iter 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) { - flags = 0; - if (!rq_iter_last(bvec, iter)) + + 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_devic 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; }

Patches currently in stable-queue which might be from axboe@fb.com are

queue-4.9/nbd-fix-use-after-free-of-rq-bio-in-the-xmit-path.patch