nghttpx: make early copy of stderr

src/shrpx.cc

@@ -564,6 +564,9 @@ void exec_binary_signal_cb(struct ev_loop *loop, ev_signal *w, int revents) {
     }
   }
 
+  // restores original stderr
+  util::restore_original_fds();
+
   if (execve(argv[0], argv.get(), envp.get()) == -1) {
     auto error = errno;
     LOG(ERROR) << "execve failed: errno=" << error;
@@ -1763,6 +1766,9 @@ int main(int argc, char **argv) {
   create_config();
   fill_default_config();
 
+  // make copy of stderr
+  util::store_original_fds();
+
   // First open log files with default configuration, so that we can
   // log errors/warnings while reading configuration files.
   reopen_log_files();

src/util.cc

@@ -657,9 +657,23 @@ std::string numeric_name(const struct sockaddr *sa, socklen_t salen) {
   return host.data();
 }
 
+static int STDERR_COPY = -1;
+static int STDOUT_COPY = -1;
+
+void store_original_fds() {
+  // consider dup'ing stdout too
+  STDERR_COPY = dup(STDERR_FILENO);
+  STDOUT_COPY = STDOUT_FILENO;
+  // no race here, since it is called early
+  make_socket_closeonexec(STDERR_COPY);
+}
+
+void restore_original_fds() {
+  dup2(STDERR_COPY, STDERR_FILENO);
+}
 
 void close_log_file(int &fd) {
-  if (fd != STDERR_FILENO && fd != STDOUT_FILENO && fd != -1) {
+  if (fd != STDERR_COPY && fd != STDOUT_COPY && fd != -1) {
     close(fd);
   }
   fd = -1;
@@ -669,12 +683,12 @@ int open_log_file(const char *path) {
 
   if (strcmp(path, "/dev/stdout") == 0 ||
       strcmp(path, "/proc/self/fd/1") == 0) {
-    return STDOUT_FILENO;
+    return STDOUT_COPY;
   }
 
   if (strcmp(path, "/dev/stderr") == 0 ||
       strcmp(path, "/proc/self/fd/2") == 0) {
-    return STDERR_FILENO;
+    return STDERR_COPY;
   }
 #if defined O_CLOEXEC
 

src/util.h

@@ -516,6 +516,14 @@ bool numeric_host(const char *hostname);
 // failed, "unknown" is returned.
 std::string numeric_name(const struct sockaddr *sa, socklen_t salen);
 
+// Makes internal copy of stderr (and possibly stdout in the future),
+// which is then used as pointer to /dev/stderr or /proc/self/fd/2
+void store_original_fds();
+
+// Restores the original stderr that was stored with copy_original_fds
+// Used just before execv
+void restore_original_fds();
+
 // Closes |fd| which was returned by open_log_file (see below)
 // and sets it to -1. In the case that |fd| points to stdout or
 // stderr, or is -1, the descriptor is not closed (but still set to -1).