From 429a787be6793554ee02aacc7e1f11ebcecc4453 Mon Sep 17 00:00:00 2001 From: Jens Axboe Date: Thu, 17 Nov 2016 12:30:37 -0700 Subject: [PATCH] nbd: fix use-after-free of rq/bio in the xmit path 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 Signed-off-by: Jens Axboe --- drivers/block/nbd.c | 32 +++++++++++++++++++++++--------- 1 file changed, 23 insertions(+), 9 deletions(-) diff --git a/drivers/block/nbd.c b/drivers/block/nbd.c index ba405b55329f..807d24a2f1de 100644 --- a/drivers/block/nbd.c +++ b/drivers/block/nbd.c @@ -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; + 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_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; } -- 2.20.1