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@vger.kernel.org
Fixes: 736ec752d95e ("AppArmor: policy routines for loading and unpacking policy")
Signed-off-by: Jann Horn <jannh@google.com>
Signed-off-by: John Johansen <john.johansen@canonical.com>

diff --git a/security/apparmor/policy_unpack.c b/security/apparmor/policy_unpack.c
index 01957ce..005a705 100644 (file)
--- a/security/apparmor/policy_unpack.c
+++ b/security/apparmor/policy_unpack.c
@@ -272,7 +272,7 @@ 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 */