[PATCH v2] nvme-tcp: fix possible data corruption with bio merges

[Sagi Grimberg]

When a bio merges, we can get a request that spans multiple
bios, and the overall request payload size is the sum of
all bios. When we calculate how much we need to send
from the existing bio (and bvec), we did not take into
account the iov_iter byte count cap.

Since multipage bvecs support, bvecs can split in the middle
which means that when we account for the last bvec send we
should also take the iov_iter byte count cap as it might be
lower than the last bvec size.

Reported-by: Hao Wang <pkuwangh at gmail.com>
Fixes: 3f2304f8c6d6 ("nvme-tcp: add NVMe over TCP host driver")
Tested-by: Hao Wang <pkuwangh at gmail.com>
Signed-off-by: Sagi Grimberg <sagi at grimberg.me>
---
 drivers/nvme/host/tcp.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

Changes from v1:
- use iov_iter_single_seg_count instead of poking into the iov_iter

diff --git a/drivers/nvme/host/tcp.c b/drivers/nvme/host/tcp.c
index 979ee31b8dd1..1ff6d6c5eb41 100644
--- a/drivers/nvme/host/tcp.c
+++ b/drivers/nvme/host/tcp.c
@@ -201,7 +201,7 @@ static inline size_t nvme_tcp_req_cur_offset(struct nvme_tcp_request *req)
 
 static inline size_t nvme_tcp_req_cur_length(struct nvme_tcp_request *req)
 {
-	return min_t(size_t, req->iter.bvec->bv_len - req->iter.iov_offset,
+	return min_t(size_t, iov_iter_single_seg_count(&req->iter),
 			req->pdu_len - req->pdu_sent);
 }
 
-- 
2.25.1