linux-kernel - [PATCH 3.2 12/94] netlink: don't compare the nul-termination in nla

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Date:	Mon, 28 Apr 2014 02:11:21 +0100
From:	Ben Hutchings <ben@...adent.org.uk>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:	akpm@...ux-foundation.org, "Thomas Graf" <tgraf@...g.ch>,
	"Pablo Neira" <pablo@...filter.org>,
	"Florian Westphal" <fw@...len.de>,
	"David S. Miller" <davem@...emloft.net>
Subject: [PATCH 3.2 12/94] netlink: don't compare the nul-termination in 
 nla_strcmp

3.2.58-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Pablo Neira <pablo@...filter.org>

[ Upstream commit 8b7b932434f5eee495b91a2804f5b64ebb2bc835 ]

nla_strcmp compares the string length plus one, so it's implicitly
including the nul-termination in the comparison.

 int nla_strcmp(const struct nlattr *nla, const char *str)
 {
        int len = strlen(str) + 1;
        ...
                d = memcmp(nla_data(nla), str, len);

However, if NLA_STRING is used, userspace can send us a string without
the nul-termination. This is a problem since the string
comparison will not match as the last byte may be not the
nul-termination.

Fix this by skipping the comparison of the nul-termination if the
attribute data is nul-terminated. Suggested by Thomas Graf.

Cc: Florian Westphal <fw@...len.de>
Cc: Thomas Graf <tgraf@...g.ch>
Signed-off-by: Pablo Neira Ayuso <pablo@...filter.org>
Signed-off-by: David S. Miller <davem@...emloft.net>
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 lib/nlattr.c | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

--- a/lib/nlattr.c
+++ b/lib/nlattr.c
@@ -299,9 +299,15 @@ int nla_memcmp(const struct nlattr *nla,
  */
 int nla_strcmp(const struct nlattr *nla, const char *str)
 {
-	int len = strlen(str) + 1;
-	int d = nla_len(nla) - len;
+	int len = strlen(str);
+	char *buf = nla_data(nla);
+	int attrlen = nla_len(nla);
+	int d;
 
+	if (attrlen > 0 && buf[attrlen - 1] == '\0')
+		attrlen--;
+
+	d = attrlen - len;
 	if (d == 0)
 		d = memcmp(nla_data(nla), str, len);
 

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