tests: fuzz etc_hosts_parse

That's just a follow-up to https://github.com/systemd/systemd/pull/22179

src/resolve/fuzz-etc-hosts.c

@@ -0,0 +1,20 @@
+/* SPDX-License-Identifier: LGPL-2.1-or-later */
+
+#include "fd-util.h"
+#include "fuzz.h"
+#include "resolved-etc-hosts.h"
+
+int LLVMFuzzerTestOneInput(const uint8_t *data, size_t size) {
+        _cleanup_fclose_ FILE *f = NULL;
+        _cleanup_(etc_hosts_free) EtcHosts h = {};
+
+        if (!getenv("SYSTEMD_LOG_LEVEL"))
+                log_set_max_level(LOG_CRIT);
+
+        f = data_to_file(data, size);
+        assert_se(f);
+
+        (void) etc_hosts_parse(&h, f);
+
+        return 0;
+}

src/resolve/meson.build

@@ -221,4 +221,11 @@ fuzzers += [
           libshared],
          [lib_openssl_or_gcrypt,
           libm]],
+        [files('fuzz-etc-hosts.c',
+          'resolved-etc-hosts.c',
+          'resolved-etc-hosts.h'),
+         [libsystemd_resolve_core,
+          libshared],
+         [lib_openssl_or_gcrypt,
+          libm]],
 ]

src/resolve/resolved-etc-hosts.c

@@ -109,7 +109,10 @@ static int parse_line(EtcHosts *hosts, unsigned nr, const char *line) {
 
                 r = dns_name_is_valid_ldh(name);
                 if (r <= 0) {
-                        log_warning_errno(r, "/etc/hosts:%u: hostname \"%s\" is not valid, ignoring.", nr, name);
+                        if (r < 0)
+                                log_warning_errno(r, "/etc/hosts:%u: Failed to check the validity of hostname \"%s\", ignoring: %m", nr, name);
+                        else
+                                log_warning("/etc/hosts:%u: hostname \"%s\" is not valid, ignoring.", nr, name);
                         continue;
                 }
 

tools/oss-fuzz.sh

@@ -73,6 +73,11 @@ done
 zip -jqr "$OUT/fuzz-bcd_seed_corpus.zip" "$bcd"
 rm -rf "$bcd"
 
+hosts=$(mktemp)
+wget -O "$hosts" https://raw.githubusercontent.com/StevenBlack/hosts/master/hosts
+zip -jq "$OUT/fuzz-etc-hosts_seed_corpus.zip" "$hosts"
+rm -rf "$hosts"
+
 # The seed corpus is a separate flat archive for each fuzzer,
 # with a fixed name ${fuzzer}_seed_corpus.zip.
 for d in "$(dirname "$0")/../test/fuzz/fuzz-"*; do