linux-kernel - [PATCH 3/4] security/selinux: decrement sizeof size in strncmp

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Message-ID: <Pine.LNX.4.64.0911120849050.16627@ask.diku.dk>
Date:	Thu, 12 Nov 2009 08:49:24 +0100 (CET)
From:	Julia Lawall <julia@...u.dk>
To:	Stephen Smalley <sds@...ho.nsa.gov>,
	James Morris <jmorris@...ei.org>,
	Eric Paris <eparis@...isplace.org>,
	linux-kernel@...r.kernel.org,
	linux-security-module@...r.kernel.org,
	kernel-janitors@...r.kernel.org
Subject: [PATCH 3/4] security/selinux: decrement sizeof size in strncmp

From: Julia Lawall <julia@...u.dk>

As observed by Joe Perches, sizeof of a constant string includes the
trailing 0.  If what is wanted is to check the initial characters of
another string, this trailing 0 should not be taken into account.  If an
exact match is wanted, strcmp should be used instead.

The semantic patch that makes this change is as follows:
(http://coccinelle.lip6.fr/)

// <smpl>
@@
expression foo;
constant char *abc;
@@

strncmp(foo, abc, 
- sizeof(abc)
+ sizeof(abc)-1
 )
// </smpl>

Signed-off-by: Julia Lawall <julia@...u.dk>

---
 security/selinux/hooks.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff -u -p a/security/selinux/hooks.c b/security/selinux/hooks.c
--- a/security/selinux/hooks.c
+++ b/security/selinux/hooks.c
@@ -448,7 +448,7 @@ static int sb_finish_set_opts(struct sup
 		sbsec->flags &= ~SE_SBLABELSUPP;
 
 	/* Special handling for sysfs. Is genfs but also has setxattr handler*/
-	if (strncmp(sb->s_type->name, "sysfs", sizeof("sysfs")) == 0)
+	if (strncmp(sb->s_type->name, "sysfs", sizeof("sysfs") - 1) == 0)
 		sbsec->flags |= SE_SBLABELSUPP;
 
 	/* Initialize the root inode. */
--
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