linux-kernel - [PATCH] netfs: Add a check for NULL folioq in netfs_writeback_unlock

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Message-ID: <ZxshMEW4U7MTgQYa@gmail.com>
Date: Thu, 24 Oct 2024 21:40:16 -0700
From: Chang Yu <marcus.yu.56@...il.com>
To: dhowells@...hat.com
Cc: jlayton@...nel.org, netfs@...ts.linux.dev,
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
	syzbot+af5c06208fa71bf31b16@...kaller.appspotmail.com,
	skhan@...uxfoundation.org
Subject: [PATCH] netfs: Add a check for NULL folioq in
 netfs_writeback_unlock_folios

syzkaller reported a null-pointer dereference bug
(https://syzkaller.appspot.com/bug?extid=af5c06208fa71bf31b16) in
netfs_writeback_unlock_folios caused by passing a NULL folioq to
folioq_folio. Fix by adding a check before entering the loop.

Signed-off-by: Chang Yu <marcus.yu.56@...il.com>
Reported-by: syzbot+af5c06208fa71bf31b16@...kaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=af5c06208fa71bf31b16
Fixes: cd0277ed0c18 ("netfs: Use new folio_queue data type and iterator instead of xarray iter")
---
 fs/netfs/write_collect.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/netfs/write_collect.c b/fs/netfs/write_collect.c
index 1d438be2e1b4..23d46a409ff2 100644
--- a/fs/netfs/write_collect.c
+++ b/fs/netfs/write_collect.c
@@ -98,7 +98,7 @@ static void netfs_writeback_unlock_folios(struct netfs_io_request *wreq,
 		slot = 0;
 	}
 
-	for (;;) {
+	while (folioq) {
 		struct folio *folio;
 		struct netfs_folio *finfo;
 		unsigned long long fpos, fend;
-- 
2.47.0