linux-kernel - [PATCH] netfs: if extracting pages from user iterator fails return 0

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Date: Fri, 24 May 2024 13:35:57 +0800
From: Lizhi Xu <lizhi.xu@...driver.com>
To: <syzbot+d2125fcb6aa8c4276fd2@...kaller.appspotmail.com>
CC: <brauner@...nel.org>, <jack@...e.cz>, <linux-fsdevel@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>, <syzkaller-bugs@...glegroups.com>,
        <viro@...iv.linux.org.uk>
Subject: [PATCH] netfs: if extracting pages from user iterator fails return 0

When extracting the pages from a user iterator fails, netfs_extract_user_iter()
will return 0, this situation will result in an abnormal and oversized return 
value for netfs_unbuffered_writer_locked() (for example, 9223372036854775807).

Therefore, when the number of extracted pages is 0, set ret to 0 and jump to out.

Reported-and-tested-by: syzbot+d2125fcb6aa8c4276fd2@...kaller.appspotmail.com
Signed-off-by: Lizhi Xu <lizhi.xu@...driver.com>
---
 fs/netfs/direct_write.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/netfs/direct_write.c b/fs/netfs/direct_write.c
index 608ba6416919..d74761fb1876 100644
--- a/fs/netfs/direct_write.c
+++ b/fs/netfs/direct_write.c
@@ -69,7 +69,7 @@ static ssize_t netfs_unbuffered_write_iter_locked(struct kiocb *iocb, struct iov
 		 */
 		if (async || user_backed_iter(iter)) {
 			n = netfs_extract_user_iter(iter, len, &wreq->iter, 0);
-			if (n < 0) {
+			if (n <= 0) {
 				ret = n;
 				goto out;
 			}
-- 
2.43.0