linux-kernel - [PATCH 3.16 68/87] apparmor: enforce nullbyte at end of tag string

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Message-ID: <lsq.1570043211.513144298@decadent.org.uk>
Date:   Wed, 02 Oct 2019 20:06:51 +0100
From:   Ben Hutchings <ben@...adent.org.uk>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:     akpm@...ux-foundation.org, Denis Kirjanov <kda@...ux-powerpc.org>,
        "John Johansen" <john.johansen@...onical.com>,
        "Jann Horn" <jannh@...gle.com>
Subject: [PATCH 3.16 68/87] apparmor: enforce nullbyte at end of tag string

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

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

From: Jann Horn <jannh@...gle.com>

commit 8404d7a674c49278607d19726e0acc0cae299357 upstream.

A packed AppArmor policy contains null-terminated tag strings that are read
by unpack_nameX(). However, unpack_nameX() uses string functions on them
without ensuring that they are actually null-terminated, potentially
leading to out-of-bounds accesses.

Make sure that the tag string is null-terminated before passing it to
strcmp().

Fixes: 736ec752d95e ("AppArmor: policy routines for loading and unpacking policy")
Signed-off-by: Jann Horn <jannh@...gle.com>
Signed-off-by: John Johansen <john.johansen@...onical.com>
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 security/apparmor/policy_unpack.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/security/apparmor/policy_unpack.c
+++ b/security/apparmor/policy_unpack.c
@@ -177,7 +177,7 @@ static bool unpack_nameX(struct aa_ext *
 		char *tag = NULL;
 		size_t size = unpack_u16_chunk(e, &tag);
 		/* if a name is specified it must match. otherwise skip tag */
-		if (name && (!size || strcmp(name, tag)))
+		if (name && (!size || tag[size-1] != '\0' || strcmp(name, tag)))
 			goto fail;
 	} else if (name) {
 		/* if a name is specified and there is no name tag fail */