libsepol: validate ocontexts

Check the literal contexts in ocontext statements are defined.

    ==91274==ERROR: AddressSanitizer: SEGV on unknown address 0x000000000000 (pc 0x7f60b0afe8c6 bp 0x7ffd42edc990 sp 0x7ffd42edc148 T0)
    ==91274==The signal is caused by a READ memory access.
    ==91274==Hint: address points to the zero page.
        #0 0x7f60b0afe8c6  string/../sysdeps/x86_64/multiarch/../strlen.S:120
        #1 0x4bd128 in __interceptor_strlen (./out/binpolicy-fuzzer+0x4bd128)
        #2 0x5eb387 in create_str_helper ./libsepol/src/kernel_to_common.c:69:10
        #3 0x5eb11e in create_str ./libsepol/src/kernel_to_common.c:99:8
        #4 0x56ad7b in context_to_str ./libsepol/src/kernel_to_conf.c:2408:9
        #5 0x56a717 in write_sid_context_rules_to_conf ./libsepol/src/kernel_to_conf.c:2441:9
        #6 0x55b26c in write_selinux_isid_rules_to_conf ./libsepol/src/kernel_to_conf.c:2476:9
        SELinuxProject#7 0x55b26c in sepol_kernel_policydb_to_conf ./libsepol/src/kernel_to_conf.c:3206:8
        SELinuxProject#8 0x55a34f in LLVMFuzzerTestOneInput ./libsepol/fuzz/binpolicy-fuzzer.c:38:9
        SELinuxProject#9 0x45aed3 in fuzzer::Fuzzer::ExecuteCallback(unsigned char const*, unsigned long) fuzzer.o
        SELinuxProject#10 0x446a12 in fuzzer::RunOneTest(fuzzer::Fuzzer*, char const*, unsigned long) fuzzer.o
        SELinuxProject#11 0x44c93b in fuzzer::FuzzerDriver(int*, char***, int (*)(unsigned char const*, unsigned long)) fuzzer.o
        SELinuxProject#12 0x475dd2 in main (./out/binpolicy-fuzzer+0x475dd2)
        SELinuxProject#13 0x7f60b0a887ec in __libc_start_main csu/../csu/libc-start.c:332:16
        SELinuxProject#14 0x423689 in _start (./out/binpolicy-fuzzer+0x423689)

Signed-off-by: Christian Göttsche <cgzones@googlemail.com>

libsepol/src/policydb_validate.c

@@ -736,6 +736,49 @@ static int validate_filename_trans_hashtab(sepol_handle_t *handle, hashtab_t fil
 	return 0;
 }
 
+static int validate_context(context_struct_t *con, validate_t flavors[], int mls)
+{
+	if (validate_value(con->user, &flavors[SYM_USERS]))
+		return -1;
+	if (validate_value(con->role, &flavors[SYM_ROLES]))
+		return -1;
+	if (validate_value(con->type, &flavors[SYM_TYPES]))
+		return -1;
+	if (mls && validate_mls_range(&con->range, &flavors[SYM_LEVELS], &flavors[SYM_CATS]))
+		return -1;
+
+	return 0;
+}
+
+static int validate_ocontexts(sepol_handle_t *handle, policydb_t *p, validate_t flavors[])
+{
+	ocontext_t *octx;
+	unsigned int i;
+
+	for (i = 0; i < OCON_NUM; i++) {
+		for (octx = p->ocontexts[i]; octx; octx = octx->next) {
+			if (validate_context(&octx->context[0], flavors, p->mls))
+				goto bad;
+
+			if (p->target_platform == SEPOL_TARGET_SELINUX) {
+				switch (i) {
+				case OCON_FS:
+				case OCON_NETIF:
+					if (validate_context(&octx->context[1], flavors, p->mls))
+						goto bad;
+					break;
+				}
+			}
+		}
+	}
+
+	return 0;
+
+bad:
+	ERR(handle, "Invalid ocontext");
+	return -1;
+}
+
 /*
  * Functions to validate a module policydb
  */
@@ -936,6 +979,9 @@ int validate_policydb(sepol_handle_t *handle, policydb_t *p)
 			goto bad;
 	}
 
+	if (validate_ocontexts(handle, p, flavors))
+		goto bad;
+
 	if (validate_scopes(handle, p->scope, p->global))
 		goto bad;