net: fix nla_strcmp to handle more then one trailing null character

[ 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@google.com>
Cc: Cong Wang <xiyou.wangcong@gmail.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: David S. Miller <davem@davemloft.net>
Cc: Jakub Kicinski <jakub.kicinski@netronome.com>
Cc: Jamal Hadi Salim <jhs@mojatatu.com>
Cc: Jiri Pirko <jiri@mellanox.com>
Cc: Jiri Pirko <jiri@resnulli.us>
Fixes: 62794fc4fbf5 ("net_sched: add max len check for TCA_KIND")
Change-Id: I66dc281f165a2858fc29a44869a270a2d698a82b
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Sasha Levin <sashal@kernel.org>

diff --git a/lib/nlattr.c b/lib/nlattr.c
index cace9b307781034df0a63b3edfe8e55c135b2ca9..0d84f79cb4b5495d05a742caaccaf28a54234e9f 100644 (file)
--- 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;