From 1a5d0fbcc08cb2d7d40ceb4937bc5c64069b0b13 Mon Sep 17 00:00:00 2001
From: bauerchen <bauerchen@tencent.com>
Date: Sun, 23 Jan 2022 15:31:51 +0800
Subject: [PATCH] backport upstream commit :722d94847de2 which fix
 CVE-2022-0185

vfs: fs_context: fix up param length parsing in legacy_parse_param
The "PAGE_SIZE - 2 - size" calculation in legacy_parse_param() is an
unsigned type so a large value of "size" results in a high positive
value instead of a negative value as expected.  Fix this by getting rid
of the subtraction.

Signed-off-by: Jamie Hill-Daniel <jamie@hill-daniel.co.uk>
Signed-off-by: William Liu <willsroot@protonmail.com>
Tested-by: Salvatore Bonaccorso <carnil@debian.org>
Tested-by: Thadeu Lima de Souza Cascardo <cascardo@canonical.com>
Acked-by: Dan Carpenter <dan.carpenter@oracle.com>
Acked-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
---
 fs/fs_context.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/fs_context.c b/fs/fs_context.c
index 138b5b4d6..a2367c7ae 100644
--- a/fs/fs_context.c
+++ b/fs/fs_context.c
@@ -585,7 +585,7 @@ static int legacy_parse_param(struct fs_context *fc, struct fs_parameter *param)
 			      param->key);
 	}
 
-	if (len > PAGE_SIZE - 2 - size)
+	if (size + len + 2 > PAGE_SIZE)
 		return invalf(fc, "VFS: Legacy: Cumulative options too large");
 	if (strchr(param->key, ',') ||
 	    (param->type == fs_value_is_string &&