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

From: Maciej Żenczykowski <redacted>

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 <redacted>
Cc: Cong Wang <redacted>
Cc: David Ahern <redacted>
Cc: David S. Miller <davem@davemloft.net>
Cc: Jakub Kicinski <redacted>
Cc: Jamal Hadi Salim <jhs@mojatatu.com>
Cc: Jiri Pirko <redacted>
Cc: Jiri Pirko <jiri@resnulli.us>
Fixes: 62794fc4fbf5 ("net_sched: add max len check for TCA_KIND")
Change-Id: I66dc281f165a2858fc29a44869a270a2d698a82b
---
 lib/nlattr.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/lib/nlattr.c b/lib/nlattr.c
index 5b6116e81f9f..1d051ef66afe 100644
--- a/lib/nlattr.c
+++ b/lib/nlattr.c

@@ -828,7 +828,7 @@ 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;

-- 
2.31.1.527.g47e6f16901-goog

Hello:

This patch was applied to netdev/net.git (refs/heads/master):

On Wed,  5 May 2021 09:58:31 -0700 you wrote:

From: Maciej Żenczykowski <redacted>

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.

[...]

Here is the summary with links:
  - net: fix nla_strcmp to handle more then one trailing null character
    https://git.kernel.org/netdev/net/c/2c16db6c92b0

You are awesome, thank you!
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