[PATCH 6.1.y 3/3] selinux: reject an unclaimed class value in security_get_classes()

[Sasha Levin <sashal@kernel.org>]

From: Bryam Vargas <hexlabsecurity@proton.me>

[ Upstream commit 22b05fec62c0fe9864cfceb52f7d0f3a34d9b1dd ]

security_get_classes() sizes an array by p_classes.nprim and fills it at
value - 1, so a class value the policy never defines leaves a NULL.
sel_make_classes() passes every entry to sel_make_dir(), reaching the same
d_alloc_name() dereference as the permission array. The class symbol table
is allowed to be sparse (policydb_class_isvalid() exists to absorb that),
but this getter builds its own array straight from the hash table and has
no such predicate.

Fail the lookup when a value went unclaimed instead of handing out the
NULL. Conforming policies define every class they declare and are
unaffected.

Cc: stable@vger.kernel.org
Fixes: 55fcf09b3fe4 ("selinux: add support for querying object classes and permissions from the running policy")
Signed-off-by: Bryam Vargas <hexlabsecurity@proton.me>
Acked-by: Stephen Smalley <stephen.smalley.work@gmail.com>
Signed-off-by: Paul Moore <paul@paul-moore.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 security/selinux/ss/services.c | 24 +++++++++++++++++++-----
 1 file changed, 19 insertions(+), 5 deletions(-)

diff --git a/security/selinux/ss/services.c b/security/selinux/ss/services.c
index 077a7af5794e6..657c8942ac810 100644
--- a/security/selinux/ss/services.c
+++ b/security/selinux/ss/services.c
@@ -3414,6 +3414,7 @@ int security_get_classes(struct selinux_policy *policy,
 			 char ***classes, u32 *nclasses)
 {
 	struct policydb *policydb;
+	u32 i;
 	int rc;
 
 	policydb = &policy->policydb;
@@ -3426,16 +3427,29 @@ int security_get_classes(struct selinux_policy *policy,
 
 	rc = hashtab_map(&policydb->p_classes.table, get_classes_callback,
 			 *classes);
-	if (rc) {
-		u32 i;
+	if (rc)
+		goto err;
 
-		for (i = 0; i < *nclasses; i++)
-			kfree((*classes)[i]);
-		kfree(*classes);
+	/*
+	 * The class symtab may be sparse, which policydb_class_isvalid() exists
+	 * to absorb; the callback fills this array by value, so an unclaimed
+	 * one leaves a NULL that sel_make_classes() hands to sel_make_dir().
+	 */
+	for (i = 0; i < *nclasses; i++) {
+		if (!(*classes)[i]) {
+			rc = -EINVAL;
+			goto err;
+		}
 	}
 
 out:
 	return rc;
+
+err:
+	for (i = 0; i < *nclasses; i++)
+		kfree((*classes)[i]);
+	kfree(*classes);
+	return rc;
 }
 
 static int get_permissions_callback(void *k, void *d, void *args)
-- 
2.53.0