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From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org, Nucca Chen <nuccachen@google.com>,
        Cong Wang <xiyou.wangcong@gmail.com>,
        David Ahern <dsahern@gmail.com>,
        "David S. Miller" <davem@davemloft.net>,
        Jakub Kicinski <jakub.kicinski@netronome.com>,
        Jamal Hadi Salim <jhs@mojatatu.com>,
        Jiri Pirko <jiri@mellanox.com>, Jiri Pirko <jiri@resnulli.us>,
        Sasha Levin <sashal@kernel.org>
Subject: [PATCH 5.4 084/141] net: fix nla_strcmp to handle more then one trailing null character
Date:   Mon, 17 May 2021 16:02:16 +0200
Message-Id: <20210517140245.610722120@linuxfoundation.org>
In-Reply-To: <20210517140242.729269392@linuxfoundation.org>
References: <20210517140242.729269392@linuxfoundation.org>
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From: Maciej Żenczykowski <maze@google.com>

[ 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>
---
 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