Patch "nbd: fix use-after-free of rq/bio in the xmit path" has been added to the 4.9-stable tree

Patch "nbd: fix use-after-free of rq/bio in the xmit path" has been added to the 4.9-stable tree

[gregkh]

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;a=summary

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