Add unpickle_megolm_outbound fuzzer. Enable C harness support.

Makefile

@@ -146,13 +146,13 @@ $(TEST_BINARIES): LDFLAGS += $(DEBUG_OPTIMIZE_FLAGS) -L$(BUILD_DIR)
 $(FUZZER_OBJECTS): CFLAGS += $(FUZZER_OPTIMIZE_FLAGS)
 $(FUZZER_OBJECTS): CXXFLAGS += $(FUZZER_OPTIMIZE_FLAGS)
 $(FUZZER_BINARIES): CPPFLAGS += -Ifuzzers/include
-$(FUZZER_BINARIES): LDFLAGS += $(FUZZER_OPTIMIZE_FLAGS) -L$(BUILD_DIR)
+$(FUZZER_BINARIES): LDFLAGS += $(FUZZER_OPTIMIZE_FLAGS) -L$(BUILD_DIR) -lstdc++
 $(FUZZER_ASAN_BINARIES): CPPFLAGS += -Ifuzzers/include
-$(FUZZER_ASAN_BINARIES): LDFLAGS += $(FUZZER_OPTIMIZE_FLAGS) -L$(BUILD_DIR)
+$(FUZZER_ASAN_BINARIES): LDFLAGS += $(FUZZER_OPTIMIZE_FLAGS) -L$(BUILD_DIR) -lstdc++
 $(FUZZER_MSAN_BINARIES): CPPFLAGS += -Ifuzzers/include
-$(FUZZER_MSAN_BINARIES): LDFLAGS += $(FUZZER_OPTIMIZE_FLAGS) -L$(BUILD_DIR)
+$(FUZZER_MSAN_BINARIES): LDFLAGS += $(FUZZER_OPTIMIZE_FLAGS) -L$(BUILD_DIR) -lstdc++
 $(FUZZER_DEBUG_BINARIES): CPPFLAGS += -Ifuzzers/include
-$(FUZZER_DEBUG_BINARIES): LDFLAGS += $(DEBUG_OPTIMIZE_FLAGS)
+$(FUZZER_DEBUG_BINARIES): LDFLAGS += $(DEBUG_OPTIMIZE_FLAGS) -lstdc++
 
 $(JS_OBJECTS): CFLAGS += $(JS_OPTIMIZE_FLAGS)
 $(JS_OBJECTS): CXXFLAGS += $(JS_OPTIMIZE_FLAGS)

fuzzers/fuzz_unpickle_megolm_outbound.c

+#include <olm/outbound_group_session.h>
+
+#include "fuzzing.h"
+
+int main(int argc, const char *argv[]) {
+    if (argc != 1) {
+      printf("Usage: %s <input_file\n", argv[0]);
+      exit(3);
+    }
+
+    void *session_buffer = malloc(olm_outbound_group_session_size());
+    OlmOutboundGroupSession *session = olm_outbound_group_session(session_buffer);
+
+    int pickle_fd = STDIN_FILENO;
+    uint8_t *pickle_buffer;
+    ssize_t pickle_length = check_errno("Error reading message file",
+                                        read_file(pickle_fd, &pickle_buffer));
+
+    check_outbound_group_session(
+        session, "Error unpickling outbound group session",
+        olm_unpickle_outbound_group_session(session, "", 0, pickle_buffer,
+                                            pickle_length));
+
+    free(session_buffer);
+    free(pickle_buffer);
+
+    return EXIT_SUCCESS;
+}

fuzzers/include/fuzzing.h

+#include "olm/olm.h"
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <unistd.h>
+#include <stddef.h>
+#include <string.h>
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <fcntl.h>
+
+#define OLM_FUZZING 1
+
+ssize_t read_file(
+    int fd,
+    uint8_t **buffer
+) {
+    size_t buffer_size = 1;
+    size_t buffer_pos = 0;
+    uint8_t * current_buffer = (uint8_t *) malloc(buffer_size);
+    if (!current_buffer) return -1;
+
+    while (1) {
+        ssize_t count = read(
+            fd, current_buffer + buffer_pos, buffer_size - buffer_pos
+        );
+
+        if (count < 0) break;  // A read error happened, so just fail immediately.
+
+        if (count == 0) {
+            // Nothing more left to read. We downsize the buffer to fit the
+            // data exactly, unless no data was read at all, in which case we
+            // skip the downsizing.
+
+            if (buffer_pos != 0) {
+                current_buffer = (uint8_t *) realloc(current_buffer, buffer_pos);
+                if (!current_buffer) break;
+            }
+
+            // The read was successful so we return the allocated buffer.
+            *buffer = current_buffer;
+            return buffer_pos;
+        }
+
+        buffer_pos += count;
+
+        // We've reached capacity, so enlarge the buffer.
+        if (buffer_pos == buffer_size) {
+            buffer_size *= 2;
+            uint8_t * new_buffer = (uint8_t *) realloc(current_buffer, buffer_size);
+            if (!new_buffer) break;
+            current_buffer = new_buffer;
+        }
+    }
+
+    free(current_buffer);
+    return -1;
+}
+
+ssize_t check_errno(
+    const char * message,
+    ssize_t value
+) {
+    if (value == (ssize_t)-1) {
+        perror(message);
+        exit(1);
+    }
+    return value;
+}
+
+size_t check_error(
+    const char * message,
+    const char * olm_message,
+    size_t value
+) {
+    if (value == olm_error()) {
+        (void)write(STDERR_FILENO, message, strlen(message));
+        (void)write(STDERR_FILENO, ": ", 2);
+        (void)write(STDERR_FILENO, olm_message, strlen(olm_message));
+        (void)write(STDERR_FILENO, "\n", 1);
+
+        exit(2);
+    }
+    return value;
+}
+
+size_t check_session(
+    OlmSession * session,
+    const char * message,
+    size_t value
+) {
+    return check_error(message, olm_session_last_error(session), value);
+}
+
+size_t check_outbound_group_session(
+    OlmOutboundGroupSession * session,
+    const char * message,
+    size_t value
+) {
+    return check_error(message, olm_outbound_group_session_last_error(session), value);
+}