fuzzers: add input size limits, always configure limits in two ways

Without the size limits, oss-fuzz creates huge samples that time out. Usually
this is because some of our code has bad algorithmic complexity. For data like
configuration samples we don't need to care about this: non-rogue configs are
rarely more than a few items, and a bit of a slowdown with a few hundred items
is acceptable. This wouldn't be OK for processing of untrusted data though.

We need to set the limit in two ways: through .options and in the code. The
first because it nicely allows libFuzzer to avoid wasting time, and the second
because fuzzers like hongfuzz and afl don't support .options.

While at it, let's fix an off-by-one (65535 is the largest offset for a
power-of-two size, but we're checking the size here).

Co-authored-by: Zbigniew Jędrzejewski-Szmek <zbyszek@in.waw.pl>

src/core/fuzz-unit-file.c

@@ -21,7 +21,11 @@ int LLVMFuzzerTestOneInput(const uint8_t *data, size_t size) {
         const char *name;
         long offset;
 
+        if (size > 65536)
+                return 0;
+
         f = data_to_file(data, size);
+
         assert_se(f);
 
         if (read_line(f, LINE_MAX, &p) < 0)

src/fuzz/fuzz-bootspec.c

@@ -84,7 +84,7 @@ int LLVMFuzzerTestOneInput(const uint8_t *data, size_t size) {
         _cleanup_(boot_config_free) BootConfig config = BOOT_CONFIG_NULL;
         int r;
 
-        if (size > 65535)
+        if (size > 65536)
                 return 0;
 
         /* Disable most logging if not running standalone */

src/fuzz/fuzz-bootspec.options

@@ -1,2 +1,2 @@
 [libfuzzer]
-max_len = 65535
+max_len = 65536

src/fuzz/fuzz-env-file.c

@@ -12,7 +12,7 @@ int LLVMFuzzerTestOneInput(const uint8_t *data, size_t size) {
         _cleanup_fclose_ FILE *f = NULL;
         _cleanup_strv_free_ char **rl = NULL, **rlp =  NULL;
 
-        if (size > 65535)
+        if (size > 65536)
                 return 0;
 
         f = data_to_file(data, size);

src/fuzz/fuzz-env-file.options

@@ -1,2 +1,2 @@
 [libfuzzer]
-max_len = 65535
+max_len = 65536

src/journal-remote/fuzz-journal-remote.c

@@ -24,7 +24,7 @@ int LLVMFuzzerTestOneInput(const uint8_t *data, size_t size) {
         _cleanup_(journal_remote_server_destroy) RemoteServer s = {};
         int r;
 
-        if (size <= 2)
+        if (size <= 2 || size > 65536)
                 return 0;
 
         if (!getenv("SYSTEMD_LOG_LEVEL"))

src/libsystemd/sd-bus/fuzz-bus-match.c

@@ -15,6 +15,9 @@ int LLVMFuzzerTestOneInput(const uint8_t *data, size_t size) {
         _cleanup_(sd_bus_unrefp) sd_bus *bus = NULL;
         int r;
 
+        if (size > 65536)
+                return 0;
+
         /* We don't want to fill the logs with messages about parse errors.
          * Disable most logging if not running standalone */
         if (!getenv("SYSTEMD_LOG_LEVEL"))

src/libsystemd/sd-bus/fuzz-bus-match.options

@@ -0,0 +1,2 @@
+[libfuzzer]
+max_len = 65536

src/network/fuzz-netdev-parser.c

@@ -11,6 +11,9 @@ int LLVMFuzzerTestOneInput(const uint8_t *data, size_t size) {
         _cleanup_fclose_ FILE *f = NULL;
         _cleanup_(unlink_tempfilep) char netdev_config[] = "/tmp/fuzz-networkd.XXXXXX";
 
+        if (size > 65536)
+                return 0;
+
         if (!getenv("SYSTEMD_LOG_LEVEL"))
                 log_set_max_level(LOG_CRIT);
 

src/network/fuzz-netdev-parser.options

@@ -0,0 +1,2 @@
+[libfuzzer]
+max_len = 65536

src/network/fuzz-network-parser.c

@@ -11,7 +11,7 @@ int LLVMFuzzerTestOneInput(const uint8_t *data, size_t size) {
         _cleanup_fclose_ FILE *f = NULL;
         _cleanup_(unlink_tempfilep) char network_config[] = "/tmp/fuzz-networkd.XXXXXX";
 
-        if (size > 65535)
+        if (size > 65536)
                 return 0;
 
         if (!getenv("SYSTEMD_LOG_LEVEL"))

src/network/fuzz-network-parser.options

@@ -1,2 +1,2 @@
 [libfuzzer]
-max_len = 65535
+max_len = 65536

src/nspawn/fuzz-nspawn-oci.c

@@ -9,6 +9,9 @@ int LLVMFuzzerTestOneInput(const uint8_t *data, size_t size) {
         _cleanup_fclose_ FILE *f = NULL;
         _cleanup_(settings_freep) Settings *s = NULL;
 
+        if (size > 65536)
+                return 0;
+
         f = data_to_file(data, size);
         assert_se(f);
 

src/nspawn/fuzz-nspawn-settings.c

@@ -9,6 +9,9 @@ int LLVMFuzzerTestOneInput(const uint8_t *data, size_t size) {
         _cleanup_fclose_ FILE *f = NULL;
         _cleanup_(settings_freep) Settings *s = NULL;
 
+        if (size > 65536)
+                return 0;
+
         f = data_to_file(data, size);
         assert_se(f);
 

src/resolve/fuzz-dns-packet.options

@@ -1,2 +1,2 @@
 [libfuzzer]
-max_len = 65535
+max_len = 65536

src/udev/fuzz-udev-rules.c

@@ -15,6 +15,9 @@ int LLVMFuzzerTestOneInput(const uint8_t *data, size_t size) {
         _cleanup_(unlink_tempfilep) char filename[] = "/tmp/fuzz-udev-rules.XXXXXX";
         int r;
 
+        if (size > 65536)
+                return 0;
+
         if (!getenv("SYSTEMD_LOG_LEVEL"))
                 log_set_max_level(LOG_CRIT);
 

src/udev/net/fuzz-link-parser.c

@@ -11,7 +11,7 @@ int LLVMFuzzerTestOneInput(const uint8_t *data, size_t size) {
         _cleanup_(unlink_tempfilep) char filename[] = "/tmp/fuzz-link-config.XXXXXX";
         _cleanup_fclose_ FILE *f = NULL;
 
-        if (size > 65535)
+        if (size > 65536)
                 return 0;
 
         if (!getenv("SYSTEMD_LOG_LEVEL"))

src/udev/net/fuzz-link-parser.options

@@ -1,2 +1,2 @@
 [libfuzzer]
-max_len = 65535
+max_len = 65536

src/xdg-autostart-generator/fuzz-xdg-desktop.c

@@ -17,6 +17,9 @@ int LLVMFuzzerTestOneInput(const uint8_t *data, size_t size) {
         _cleanup_(xdg_autostart_service_freep) XdgAutostartService *service = NULL;
         _cleanup_(rm_rf_physical_and_freep) char *tmpdir = NULL;
 
+        if (size > 65536)
+                return 0;
+
         /* We don't want to fill the logs with messages about parse errors.
          * Disable most logging if not running standalone */
         if (!getenv("SYSTEMD_LOG_LEVEL"))

src/xdg-autostart-generator/fuzz-xdg-desktop.options

@@ -0,0 +1,2 @@
+[libfuzzer]
+max_len = 65536