OSS-Fuzz: Add new fuzzer targets ip forwarding rule parsing

Signed-off-by: Arthur Chan <arthur.chan@adalogics.com>

tests/fuzzing/ipfw-rule-fuzz.c

@@ -0,0 +1,73 @@
+/*
+ * Copyright (C) 2019-2026 by Sukchan Lee <acetcom@gmail.com>
+ *
+ * This file is part of Open5GS.
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Affero General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+/*
+ * IPFilterRule flow-description parser fuzz target.
+ *
+ * A PCC rule carries its packet filter as an IPFilterRule text string, which
+ * reaches the SMF from the PCF over N7 and from the PGW over Gx.
+ * ogs_ipfw_compile_rule() tokenises that string and hands it to compile_rule()
+ * in the bundled FreeBSD ipfw parser, so the whole of lib/ipfw parses remote
+ * input. No existing fuzz target links lib/ipfw, so none of it is instrumented.
+ *
+ * The bundled parser redefines errx() as a log call (lib/ipfw/ipfw2.c), so the
+ * paths FreeBSD ends with a fatal error instead continue with whatever state
+ * they had reached. That makes the error paths worth exercising, not just the
+ * accepting ones.
+ */
+
+#include <stdio.h>
+#include <stdint.h>
+
+#include "fuzzing.h"
+#include "ipfw/ogs-ipfw.h"
+
+/* "permit out" is the shortest prefix the parser accepts. */
+#define kMinInputLength 4
+#define kMaxInputLength 512
+
+extern int LLVMFuzzerTestOneInput(const uint8_t *Data, size_t Size)
+{
+    char *flow_description;
+    ogs_ipfw_rule_t ipfw_rule;
+
+    if (Size < kMinInputLength || Size > kMaxInputLength) {
+        return 1;
+    }
+
+    if (!initialized) {
+        initialize();
+    }
+
+    /* The parser uses ogs_strtok_r() and strcmp(), so the input has to be a
+     * NUL-terminated string. An exact-size allocation keeps a read past the
+     * terminator detectable. */
+    flow_description = ogs_malloc(Size + 1);
+    if (flow_description == NULL) {
+        return 1;
+    }
+    memcpy(flow_description, Data, Size);
+    flow_description[Size] = '\0';
+
+    ogs_ipfw_compile_rule(&ipfw_rule, flow_description);
+
+    ogs_free(flow_description);
+
+    return 0;
+}

tests/fuzzing/meson.build

@@ -28,6 +28,7 @@ pfcp_message_source = files('pfcp-message-fuzz.c')
 nas_5gs_message_source = files('nas-5gs-message-fuzz.c')
 sbi_nf_profile_source = files('sbi-nf-profile-fuzz.c')
 sbi_sm_context_source = files('sbi-sm-context-fuzz.c')
+ipfw_rule_source = files('ipfw-rule-fuzz.c')
 
 # Build all executable
 executable(
@@ -93,3 +94,11 @@ executable(
     dependencies : [libsbi_dep, libcore_dep],
     link_args: lib_fuzzing_engine
 )
+
+executable(
+    'ipfw_rule_fuzz',
+    sources : ipfw_rule_source,
+    c_args : [testunit_core_cc_flags, sbi_cc_flags],
+    dependencies : [libipfw_dep, libproto_dep, libcore_dep],
+    link_args: lib_fuzzing_engine
+)