conf: warn if not having read-only access to keys

After dropping root privileges, log a warning message if chronyd
doesn't have read access or has (unnecessary) write access to the
files containing symmetric and server NTS keys.

conf.c

@@ -1774,6 +1774,19 @@ CNF_CreateDirs(uid_t uid, gid_t gid)
 
 /* ================================================== */
 
+void
+CNF_CheckReadOnlyAccess(void)
+{
+  unsigned int i;
+
+  if (keys_file)
+    UTI_CheckReadOnlyAccess(keys_file);
+  for (i = 0; i < ARR_GetSize(nts_server_key_files); i++)
+    UTI_CheckReadOnlyAccess(*(char **)ARR_GetElement(nts_server_key_files, i));
+}
+
+/* ================================================== */
+
 void
 CNF_AddInitSources(void)
 {

conf.h

@@ -44,6 +44,8 @@ extern void CNF_ParseLine(const char *filename, int number, char *line);
 
 extern void CNF_CreateDirs(uid_t uid, gid_t gid);
 
+extern void CNF_CheckReadOnlyAccess(void);
+
 extern void CNF_AddInitSources(void);
 extern void CNF_AddSources(void);
 extern void CNF_AddBroadcasts(void);

main.c

@@ -637,9 +637,13 @@ int main
   }
 
   /* Drop root privileges if the specified user has a non-zero UID */
-  if (!geteuid() && (pw->pw_uid || pw->pw_gid))
+  if (!geteuid() && (pw->pw_uid || pw->pw_gid)) {
     SYS_DropRoot(pw->pw_uid, pw->pw_gid, SYS_MAIN_PROCESS);
 
+    /* Warn if missing read access or having write access to keys */
+    CNF_CheckReadOnlyAccess();
+  }
+
   if (!geteuid())
     LOG(LOGS_WARN, "Running with root privileges");
 

util.c

@@ -1271,6 +1271,17 @@ UTI_CheckFilePermissions(const char *path, mode_t perm)
 
 /* ================================================== */
 
+void
+UTI_CheckReadOnlyAccess(const char *path)
+{
+  if (access(path, R_OK) != 0 && errno != ENOENT)
+    LOG(LOGS_WARN, "Missing read access to %s : %s", path, strerror(errno));
+  if (access(path, W_OK) == 0)
+    LOG(LOGS_WARN, "Having write access to %s", path);
+}
+
+/* ================================================== */
+
 static int
 join_path(const char *basedir, const char *name, const char *suffix,
           char *buffer, size_t length, LOG_Severity severity)

util.h

@@ -200,6 +200,10 @@ extern int UTI_CheckDirPermissions(const char *path, mode_t perm, uid_t uid, gid
    specified.  It does not return error if it is not an accessible file. */
 extern int UTI_CheckFilePermissions(const char *path, mode_t perm);
 
+/* Log a warning message if not having read access or having write access
+   to a file/directory */
+extern void UTI_CheckReadOnlyAccess(const char *path);
+
 /* Open a file.  The full path of the file is constructed from the basedir
    (may be NULL), '/' (if basedir is not NULL), name, and suffix (may be NULL).
    Created files have specified permissions (umasked).  Returns NULL on error.