[PATCH 5.4 084/141] net: fix nla_strcmp to handle more then one trailing null character

[Greg Kroah-Hartman]

From: Maciej Żenczykowski <maze@xxxxxxxxxx>

[ Upstream commit 2c16db6c92b0ee4aa61e88366df82169e83c3f7e ]

Android userspace has been using TCA_KIND with a char[IFNAMESIZ]
many-null-terminated buffer containing the string 'bpf'.

This works on 4.19 and ceases to work on 5.10.

I'm not entirely sure what fixes tag to use, but I think the issue
was likely introduced in the below mentioned 5.4 commit.

Reported-by: Nucca Chen <nuccachen@xxxxxxxxxx>
Cc: Cong Wang <xiyou.wangcong@xxxxxxxxx>
Cc: David Ahern <dsahern@xxxxxxxxx>
Cc: David S. Miller <davem@xxxxxxxxxxxxx>
Cc: Jakub Kicinski <jakub.kicinski@xxxxxxxxxxxxx>
Cc: Jamal Hadi Salim <jhs@xxxxxxxxxxxx>
Cc: Jiri Pirko <jiri@xxxxxxxxxxxx>
Cc: Jiri Pirko <jiri@xxxxxxxxxxx>
Fixes: 62794fc4fbf5 ("net_sched: add max len check for TCA_KIND")
Change-Id: I66dc281f165a2858fc29a44869a270a2d698a82b
Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
 lib/nlattr.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/lib/nlattr.c b/lib/nlattr.c
index cace9b307781..0d84f79cb4b5 100644
--- a/lib/nlattr.c
+++ b/lib/nlattr.c
@@ -609,7 +609,7 @@ int nla_strcmp(const struct nlattr *nla, const char *str)
 	int attrlen = nla_len(nla);
 	int d;
 
-	if (attrlen > 0 && buf[attrlen - 1] == '\0')
+	while (attrlen > 0 && buf[attrlen - 1] == '\0')
 		attrlen--;
 
 	d = attrlen - len;
-- 
2.30.2