4.9-stable review patch. If anyone has any objections, please let me know.
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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; }