crypto-util: support OpenSSL 4

OpenSSL 4 broke ABI, so we need to look for both SONAMEs.
Try libcrypto.so.3 first, and fallback to libcrypto.so.4,
so that the older and more stable version is used if both
are installed, giving distros time to fix regressions.

src/shared/crypto-util.c

@@ -335,12 +335,15 @@ DEFINE_TRIVIAL_CLEANUP_FUNC_FULL_RENAME(UI_METHOD*, sym_UI_destroy_method, UI_de
 int dlopen_libcrypto(int log_level) {
 #if HAVE_OPENSSL
         static void *libcrypto_dl = NULL;
+        int r;
 
         LIBCRYPTO_NOTE(SD_ELF_NOTE_DLOPEN_PRIORITY_SUGGESTED);
 
-        return dlopen_many_sym_or_warn(
+        // FIXME: switch order to prefer libcrypto.so.4 in a future version once it has stabilized
+        FOREACH_STRING(soname, "libcrypto.so.3", "libcrypto.so.4") {
+                r = dlopen_many_sym_or_warn(
                         &libcrypto_dl,
-                        "libcrypto.so.3",
+                        soname,
                         log_level,
                         DLSYM_ARG(ASN1_ANY_it),
                         DLSYM_ARG(ASN1_BIT_STRING_it),
@@ -617,6 +620,15 @@ int dlopen_libcrypto(int log_level) {
                         DLSYM_ARG(X509_VERIFY_PARAM_set_hostflags),
                         DLSYM_ARG(X509_VERIFY_PARAM_set1_host),
                         DLSYM_ARG(X509_VERIFY_PARAM_set1_ip));
+                if (r >= 0)
+                        break;
+        }
+        if (r < 0) {
+                log_full_errno(log_level, r, "Neither libcrypto.so.4 nor libcrypto.so.3 could be loaded");
+                return -EOPNOTSUPP; /* turn into recognizable error */
+        }
+
+        return r;
 #else
         return log_full_errno(log_level, SYNTHETIC_ERRNO(EOPNOTSUPP),
                               "libcrypto support is not compiled in.");

src/shared/crypto-util.h

@@ -37,7 +37,7 @@ int dlopen_libcrypto(int log_level);
         SD_ELF_NOTE_DLOPEN("libcrypto",                                 \
                            "Support for cryptographic operations",      \
                            priority,                                    \
-                           "libcrypto.so.3")
+                           "libcrypto.so.3", "libcrypto.so.4")
 
 #define DLOPEN_LIBCRYPTO(log_level, priority)                           \
         ({                                                              \