stream_file: allow to open only our fd in case of fuzzing

This ensures that we don't open some other fd, for example when loading
playlist. Also filters out loading any local files.

This also allows to remove custom filtering from fuzzer itself.

fuzzers/fuzzer_load.c

@@ -45,6 +45,9 @@ int LLVMFuzzerTestOneInput(const uint8_t *data, size_t size)
     int fd = memfd_create("fuzz_mpv_load", MFD_CLOEXEC | MFD_ALLOW_SEALING);
     if (fd == -1)
         exit(1);
+    if (dup3(fd, 42, O_CLOEXEC) != 42 || close(fd))
+        exit(1);
+    fd = 42;
     ssize_t written = 0;
     while (written < size) {
         ssize_t result = write(fd, data + written, size - written);
@@ -85,7 +88,9 @@ int LLVMFuzzerTestOneInput(const uint8_t *data, size_t size)
 #endif
 
     mpv_terminate_destroy(ctx);
-    close(fd);
+
+    if (close(fd))
+        exit(1);
 
     return 0;
 }

fuzzers/fuzzer_loadfile_direct.c

@@ -38,26 +38,6 @@ int LLVMFuzzerTestOneInput(const uint8_t *data, size_t size)
         return 0;
 #endif
 
-#if !defined(MPV_PROTO) || defined(MPV_PROTO_FILE)
-    const uint8_t *data_check = data;
-    size_t size_check = size;
-    size_t prefix_size = sizeof("file://") - 1;
-    if (str_startswith(data, size - 1, "file://", prefix_size)) {
-        data_check += prefix_size;
-        size_check -= prefix_size;
-    }
-    // Exclude some common paths that are not useful for testing.
-    // Exclude -
-    if (size_check == 2 && !strncmp(data_check, "-", 1))
-        return 0;
-    // Exclude relative paths
-    if (str_startswith(data_check, size_check - 1, ".", 1))
-        return 0;
-    // Exclude absolute paths
-    if (str_startswith(data_check, size_check - 1, "/", 1))
-        return 0;
-#endif
-
     mpv_handle *ctx = mpv_create();
     if (!ctx)
         exit(1);

player/loadfile.c

@@ -1182,18 +1182,6 @@ static void start_open(struct MPContext *mpctx, char *url, int url_flags,
     mpctx->open_for_prefetch = for_prefetch && mpctx->opts->demuxer_thread;
     mpctx->demuxer_changed = false;
 
-#ifdef FUZZING_BUILD_MODE_UNSAFE_FOR_PRODUCTION
-    // Don't allow to open local paths or stdin during fuzzing
-    bstr open_url = bstr0(mpctx->open_url);
-    if (bstr_startswith0(open_url, "/") ||
-        bstr_startswith0(open_url, ".") ||
-        bstr_equals0(open_url, "-"))
-    {
-        cancel_open(mpctx);
-        return;
-    }
-#endif
-
     if (mp_thread_create(&mpctx->open_thread, open_demux_thread, mpctx)) {
         cancel_open(mpctx);
         return;

stream/stream_file.c

@@ -309,10 +309,6 @@ static int open_f(stream_t *stream, const struct stream_open_args *args)
             MP_ERR(stream, "Invalid FD: %d\n", p->fd);
             return STREAM_ERROR;
         }
-#endif
-#ifdef FUZZING_BUILD_MODE_UNSAFE_FOR_PRODUCTION
-        if (p->fd == STDIN_FILENO || p->fd == STDOUT_FILENO || p->fd == STDERR_FILENO)
-            return STREAM_ERROR;
 #endif
         if (is_fdclose)
             p->close = true;
@@ -344,6 +340,13 @@ static int open_f(stream_t *stream, const struct stream_open_args *args)
         p->close = true;
     }
 
+#ifdef FUZZING_BUILD_MODE_UNSAFE_FOR_PRODUCTION
+    if (p->fd != 42) {
+        s_close(stream);
+        return STREAM_ERROR;
+    }
+#endif
+
     struct stat st;
     bool is_sock_or_fifo = false;
     if (fstat(p->fd, &st) == 0) {