[PATCH 2/2] libsepol: Check kernel to CIL and Conf functions for supported versions

[James Carter <jwcart2@xxxxxxxxx>]

For policy versions between 20 and 23, attributes exist in the
policy, but only in the type_attr_map. This means that there are
gaps in both the type_val_to_struct and p_type_val_to_name arrays
and policy rules can refer to those gaps which can lead to NULL
dereferences when using sepol_kernel_policydb_to_conf() and
sepol_kernel_policydb_to_cil().

This can be seen with the following policy:
  class CLASS1
  sid SID1
  class CLASS1 { PERM1 }
  attribute TYPE_ATTR1;
  type TYPE1;
  typeattribute TYPE1 TYPE_ATTR1;
  allow TYPE_ATTR1 self : CLASS1 PERM1;
  role ROLE1;
  role ROLE1 types TYPE1;
  user USER1 roles ROLE1;
  sid SID1 USER1:ROLE1:TYPE1

Compile the policy:
  checkpolicy -c 23 -o policy.bin policy.conf
Converting back to a policy.conf causes a segfault:
  checkpolicy -F -b -o policy.bin.conf policy.bin

Have both sepol_kernel_policydb_to_conf() and
sepol_kernel_policydb_to_cil() exit with an error if the kernel
policy version is between 20 and 23.

Signed-off-by: James Carter <jwcart2@xxxxxxxxx>
---
 libsepol/src/kernel_to_cil.c  | 12 ++++++++++++
 libsepol/src/kernel_to_conf.c | 12 ++++++++++++
 2 files changed, 24 insertions(+)

diff --git a/libsepol/src/kernel_to_cil.c b/libsepol/src/kernel_to_cil.c
index a146ac51..edfebeaf 100644
--- a/libsepol/src/kernel_to_cil.c
+++ b/libsepol/src/kernel_to_cil.c
@@ -3164,6 +3164,18 @@ int sepol_kernel_policydb_to_cil(FILE *out, struct policydb *pdb)
 		goto exit;
 	}
 
+	if (pdb->policyvers >= POLICYDB_VERSION_AVTAB && pdb->policyvers <= POLICYDB_VERSION_PERMISSIVE) {
+		/*
+		 * For policy versions between 20 and 23, attributes exist in the policy,
+		 * but only in the type_attr_map. This means that there are gaps in both
+		 * the type_val_to_struct and p_type_val_to_name arrays and policy rules
+		 * can refer to those gaps.
+		 */
+		sepol_log_err("Writing policy versions between 20 and 23 as CIL is not supported");
+		rc = -1;
+		goto exit;
+	}
+
 	rc = constraint_rules_to_strs(pdb, mls_constraints, non_mls_constraints);
 	if (rc != 0) {
 		goto exit;
diff --git a/libsepol/src/kernel_to_conf.c b/libsepol/src/kernel_to_conf.c
index a22f196d..ea58a026 100644
--- a/libsepol/src/kernel_to_conf.c
+++ b/libsepol/src/kernel_to_conf.c
@@ -3041,6 +3041,18 @@ int sepol_kernel_policydb_to_conf(FILE *out, struct policydb *pdb)
 		goto exit;
 	}
 
+	if (pdb->policyvers >= POLICYDB_VERSION_AVTAB && pdb->policyvers <= POLICYDB_VERSION_PERMISSIVE) {
+		/*
+		 * For policy versions between 20 and 23, attributes exist in the policy,
+		 * but only in the type_attr_map. This means that there are gaps in both
+		 * the type_val_to_struct and p_type_val_to_name arrays and policy rules
+		 * can refer to those gaps.
+		 */
+		sepol_log_err("Writing policy versions between 20 and 23 as a policy.conf is not supported");
+		rc = -1;
+		goto exit;
+	}
+
 	rc = constraint_rules_to_strs(pdb, mls_constraints, non_mls_constraints);
 	if (rc != 0) {
 		goto exit;
-- 
2.26.2