linux-kernel - [PATCH] apparmor: enforce nullbyte at end of tag string

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Message-Id: <20190528153226.248785-1-jannh@google.com>
Date:   Tue, 28 May 2019 17:32:26 +0200
From:   Jann Horn <jannh@...gle.com>
To:     John Johansen <john.johansen@...onical.com>, jannh@...gle.com
Cc:     "Serge E. Hallyn" <serge@...lyn.com>,
        linux-security-module@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH] apparmor: enforce nullbyte at end of tag string

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().

Cc: stable@...r.kernel.org
Signed-off-by: Jann Horn <jannh@...gle.com>
---
Warning: The existence of this bug has not been verified at runtime, and
the patch is compile-tested only. I noticed this while browsing through
the code, but didn't want to spend the time necessary to figure out how
to actually test this at runtime.


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

diff --git a/security/apparmor/policy_unpack.c b/security/apparmor/policy_unpack.c
index f6c2bcb2ab14..33041c4fb69f 100644
--- a/security/apparmor/policy_unpack.c
+++ b/security/apparmor/policy_unpack.c
@@ -276,7 +276,7 @@ static bool unpack_nameX(struct aa_ext *e, enum aa_code code, const char *name)
 		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 */
-- 
2.22.0.rc1.257.g3120a18244-goog