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

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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>
This commit is contained in:
Jens Axboe 2016-11-17 12:30:37 -07:00
parent 4121d385f1
commit 429a787be6
1 changed files with 23 additions and 9 deletions
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32
drivers/block/nbd.c
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@ -272,6 +272,7 @@ static int nbd_send_cmd(struct nbd_device *nbd, struct nbd_cmd *cmd)
int result, flags; int result, flags;
struct nbd_request request; struct nbd_request request;
unsigned long size = blk_rq_bytes(req); unsigned long size = blk_rq_bytes(req);
struct bio *bio;
u32 type; u32 type;
if (req->cmd_type == REQ_TYPE_DRV_PRIV) 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; return -EIO;
} }
if (type == NBD_CMD_WRITE) { if (type != NBD_CMD_WRITE)
struct req_iterator iter; return 0;
flags = 0;
bio = req->bio;
while (bio) {
struct bio *next = bio->bi_next;
struct bvec_iter iter;
struct bio_vec bvec; struct bio_vec bvec;
/*
* we are really probing at internals to determine bio_for_each_segment(bvec, bio, iter) {
* whether to set MSG_MORE or not... bool is_last = !next && bio_iter_last(bvec, iter);
*/
rq_for_each_segment(bvec, req, iter) { if (is_last)
flags = 0;
if (!rq_iter_last(bvec, iter))
flags = MSG_MORE; flags = MSG_MORE;
dev_dbg(nbd_to_dev(nbd), "request %p: sending %d bytes data\n", dev_dbg(nbd_to_dev(nbd), "request %p: sending %d bytes data\n",
cmd, bvec.bv_len); cmd, bvec.bv_len);
@ -325,7 +330,16 @@ static int nbd_send_cmd(struct nbd_device *nbd, struct nbd_cmd *cmd)
result); result);
return -EIO; 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; return 0;
} }