linux-kernel - [PATCH 2/2] iov: Fix netfs_extract_user_to

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Message-Id: <20230227130454.2673622-3-dhowells@redhat.com>
Date:   Mon, 27 Feb 2023 13:04:54 +0000
From:   David Howells <dhowells@...hat.com>
To:     Steve French <smfrench@...il.com>
Cc:     David Howells <dhowells@...hat.com>,
        Shyam Prasad N <nspmangalore@...il.com>,
        Rohith Surabattula <rohiths.msft@...il.com>,
        Tom Talpey <tom@...pey.com>,
        Stefan Metzmacher <metze@...ba.org>,
        Jeff Layton <jlayton@...nel.org>, linux-cifs@...r.kernel.org,
        linux-kernel@...r.kernel.org, kernel test robot <lkp@...el.com>,
        Dan Carpenter <error27@...il.com>,
        Steve French <sfrench@...ba.org>, linux-cachefs@...hat.com
Subject: [PATCH 2/2] iov: Fix netfs_extract_user_to_sg()

Fix the loop check in netfs_extract_user_to_sg() for extraction from
user-backed iterators to do the body if npages > 0, not if npages < 0
(which it can never be).

This isn't currently used by cifs, which only ever extracts data from BVEC,
KVEC and XARRAY iterators at this level, user-backed iterators having being
decanted into BVEC iterators at a higher level to accommodate the work
being done in a kernel thread.

Found by smatch:
	fs/netfs/iterator.c:139 netfs_extract_user_to_sg() warn: unsigned 'npages' is never less than zero.

Fixes: 018584697533 ("netfs: Add a function to extract an iterator into a scatterlist")
Reported-by: kernel test robot <lkp@...el.com>
Reported-by: Dan Carpenter <error27@...il.com>
Signed-off-by: David Howells <dhowells@...hat.com>
cc: Steve French <sfrench@...ba.org>
cc: Jeff Layton <jlayton@...nel.org>
cc: linux-cifs@...r.kernel.org
cc: linux-cachefs@...hat.com
Link: https://lore.kernel.org/oe-kbuild-all/202302261115.P3TQi1ZO-lkp@intel.com/
---
 fs/netfs/iterator.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/netfs/iterator.c b/fs/netfs/iterator.c
index f00d43b8ac0a..e9a45dea748a 100644
--- a/fs/netfs/iterator.c
+++ b/fs/netfs/iterator.c
@@ -134,7 +134,7 @@ static ssize_t netfs_extract_user_to_sg(struct iov_iter *iter,
 		npages = DIV_ROUND_UP(off + len, PAGE_SIZE);
 		sg_max -= npages;
 
-		for (; npages < 0; npages--) {
+		for (; npages > 0; npages--) {
 			struct page *page = *pages;
 			size_t seg = min_t(size_t, PAGE_SIZE - off, len);