[PATCH 5.4 04/15] vfs: fs_context: fix up param length parsing in legacy_parse_param

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

From: Jamie Hill-Daniel <jamie@hill-daniel.co.uk>

commit 722d94847de29310e8aa03fcbdb41fc92c521756 upstream.

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: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 fs/fs_context.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/fs/fs_context.c
+++ b/fs/fs_context.c
@@ -585,7 +585,7 @@ static int legacy_parse_param(struct fs_
 			      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 &&