[PATCH v2] cifs: Fix cifs_limit_bvec_subset() to correctly check the maxmimum size

[David Howells]

Fix cifs_limit_bvec_subset() so that it limits the span to the maximum
specified and won't return with a size greater than max_size.

Fixes: d08089f649a0 ("cifs: Change the I/O paths to use an iterator rather than a page list")
Reported-by: Shyam Prasad N <sprasad@xxxxxxxxxxxxx>
Signed-off-by: David Howells <dhowells@xxxxxxxxxx>
cc: Steve French <smfrench@xxxxxxxxx>
cc: Rohith Surabattula <rohiths.msft@xxxxxxxxx>
cc: Paulo Alcantara <pc@xxxxxxxxxxxxx>
cc: Tom Talpey <tom@xxxxxxxxxx>
cc: Jeff Layton <jlayton@xxxxxxxxxx>
cc: linux-cifs@xxxxxxxxxxxxxxx
cc: linux-fsdevel@xxxxxxxxxxxxxxx
---
 fs/cifs/file.c |    3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/fs/cifs/file.c b/fs/cifs/file.c
index ba7f2e09d6c8..df88b8c04d03 100644
--- a/fs/cifs/file.c
+++ b/fs/cifs/file.c
@@ -3353,9 +3353,10 @@ static size_t cifs_limit_bvec_subset(const struct iov_iter *iter, size_t max_siz
 	while (n && ix < nbv) {
 		len = min3(n, bvecs[ix].bv_len - skip, max_size);
 		span += len;
+		max_size -= len;
 		nsegs++;
 		ix++;
-		if (span >= max_size || nsegs >= max_segs)
+		if (max_size == 0 || nsegs >= max_segs)
 			break;
 		skip = 0;
 		n -= len;