[RFC,v2,20/22] selinux: more strict bounds check

Commit Message

Christian Göttsche Dec. 16, 2024, 4:40 p.m. UTC

From: Christian Göttsche <[e-mail]>

Validate the types used in bounds checks.
Replace the usage of BUG(), to avoid halting the system on malformed
polices.

Signed-off-by: Christian Göttsche <[e-mail]>
---
 security/selinux/ss/policydb.c | 29 +++++++++++++++++++++++++++--
 security/selinux/ss/policydb.h |  1 +
 security/selinux/ss/services.c |  3 +++
 3 files changed, 31 insertions(+), 2 deletions(-)

Patch

diff --git a/security/selinux/ss/policydb.c b/security/selinux/ss/policydb.c
index e9e478650e74..57ab2a811a15 100644
--- a/security/selinux/ss/policydb.c
+++ b/security/selinux/ss/policydb.c
@@ -1020,6 +1020,15 @@  bool policydb_class_isvalid(const struct policydb *p, u16 class)
 	return true;
 }
 
+bool policydb_user_isvalid(const struct policydb *p, u32 user)
+{
+	if (!user || user > p->p_roles.nprim)
+		return false;
+	if (!p->sym_val_to_name[SYM_USERS][user - 1])
+		return false;
+	return true;
+}
+
 bool policydb_role_isvalid(const struct policydb *p, u32 role)
 {
 	if (!role || role > p->p_roles.nprim)
@@ -1940,6 +1949,12 @@  static int user_bounds_sanity_check(void *key, void *datum, void *datap)
 			return -EINVAL;
 		}
 
+		if (!policydb_user_isvalid(p, upper->bounds)) {
+			pr_err("SELinux: user %s: invalid boundary id %d\n",
+			       (char *) key, upper->bounds);
+			return -EINVAL;
+		}
+
 		upper = p->user_val_to_struct[upper->bounds - 1];
 		ebitmap_for_each_positive_bit(&user->roles, node, bit)
 		{
@@ -1977,6 +1992,12 @@  static int role_bounds_sanity_check(void *key, void *datum, void *datap)
 			return -EINVAL;
 		}
 
+		if (!policydb_role_isvalid(p, upper->bounds)) {
+			pr_err("SELinux: role %s: invalid boundary id %d\n",
+			       (char *) key, upper->bounds);
+			return -EINVAL;
+		}
+
 		upper = p->role_val_to_struct[upper->bounds - 1];
 		ebitmap_for_each_positive_bit(&role->types, node, bit)
 		{
@@ -2011,9 +2032,13 @@  static int type_bounds_sanity_check(void *key, void *datum, void *datap)
 			return -EINVAL;
 		}
 
-		upper = p->type_val_to_struct[upper->bounds - 1];
-		BUG_ON(!upper);
+		if (!policydb_type_isvalid(p, upper->bounds)) {
+			pr_err("SELinux: type %s: invalid boundary id %d\n",
+			       (char *) key, upper->bounds);
+			return -EINVAL;
+		}
 
+		upper = p->type_val_to_struct[upper->bounds - 1];
 		if (upper->attribute) {
 			pr_err("SELinux: type %s: "
 			       "bounded by attribute %s\n",
diff --git a/security/selinux/ss/policydb.h b/security/selinux/ss/policydb.h
index aa3b21bd5286..512d2081733b 100644
--- a/security/selinux/ss/policydb.h
+++ b/security/selinux/ss/policydb.h
@@ -323,6 +323,7 @@  extern bool policydb_context_isvalid(const struct policydb *p, const struct cont
 extern bool policydb_class_isvalid(const struct policydb *p, u16 class);
 extern bool policydb_type_isvalid(const struct policydb *p, u32 type);
 extern bool policydb_role_isvalid(const struct policydb *p, u32 role);
+extern bool policydb_user_isvalid(const struct policydb *p, u32 user);
 extern bool policydb_boolean_isvalid(const struct policydb *p, u32 boolean);
 extern int policydb_read(struct policydb *p, struct policy_file *fp);
 extern int policydb_write(struct policydb *p, struct policy_file *fp);
diff --git a/security/selinux/ss/services.c b/security/selinux/ss/services.c
index 227fe7832c08..6dd281ddef7a 100644
--- a/security/selinux/ss/services.c
+++ b/security/selinux/ss/services.c
@@ -711,6 +711,9 @@  static void context_struct_compute_av(struct policydb *policydb,
 	 * If the given source and target types have boundary
 	 * constraint, lazy checks have to mask any violated
 	 * permission and notice it to userspace via audit.
+	 *
+	 * Infinite recursion is avoided via a depth pre-check in
+	 * type_bounds_sanity_check().
 	 */
 	type_attribute_bounds_av(policydb, scontext, tcontext,
 				 tclass, avd);