OVAL/probes/sysctl: Gracefully handle non-hybrid offline mode

In case the probe for some reason is executed against an offline
system image we won't want it to break the entire scan process
but rather quietly not yield any results.

Author: evgenyz

src/OVAL/probes/unix/sysctl_probe.c

@@ -53,6 +53,7 @@
 #include <ctype.h>
 #include <errno.h>
 #include <limits.h>
+#include <dirent.h>
 #include "oval_fts.h"
 #include "common/debug_priv.h"
 
@@ -128,13 +129,22 @@ int sysctl_probe_main(probe_ctx *ctx, void *probe_arg)
         ofts = oval_fts_open_prefixed(prefix, path_entity, filename_entity, NULL, bh_entity, probe_ctx_getresult(ctx));
 
         if (ofts == NULL) {
-                dE("oval_fts_open_prefixed(%s, %s) (prefix: %s) failed", PROC_SYS_DIR, ".\\+", prefix);
                 SEXP_free(path_entity);
                 SEXP_free(filename_entity);
                 SEXP_free(bh_entity);
                 SEXP_free(name_entity);
 
-                return (PROBE_EFATAL);
+                if (prefix != NULL) {
+                        DIR *d = opendir(prefix);
+                        if (d != NULL) {
+                                closedir(d);
+                                return PROBE_ESUCCESS;
+                        }
+                        dW("Can't open prefix directory '%s': %s", prefix, strerror(errno));
+                }
+
+                dE("oval_fts_open_prefixed(%s, %s, %s, ...) failed", prefix, PROC_SYS_DIR, ".*");
+                return PROBE_EFATAL;
         }
 
         while ((ofts_ent = oval_fts_read(ofts)) != NULL) {