Bug#876365: Ubuntu patch

[Bryce Harrington]

This is a fix we have carried in the Ubuntu nginx package for this
issue.  If Debian can pick up this patch it'll help reduce the delta on
the Ubuntu side.

Bryce
Description: Fix NGINX pidfile handling
Author: Tj <ubu...@iam.tj>
Bug-Ubuntu: https://bugs.launchpad.net/ubuntu/+source/nginx/+bug/1581864
Bug-Debian: https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=876365
Last-Update: 2020-06-24
---
This patch header follows DEP-3: http://dep.debian.net/deps/dep3/
diff --git a/src/core/nginx.c b/src/core/nginx.c
index 9fcb0eb2..083eba1d 100644
--- a/src/core/nginx.c
+++ b/src/core/nginx.c
@@ -338,14 +338,21 @@ main(int argc, char *const *argv)
         ngx_process = NGX_PROCESS_MASTER;
     }
 
+    /* tell-tale to detect if this is parent or child process */
+    ngx_int_t child_pid = NGX_BUSY;
+
 #if !(NGX_WIN32)
 
     if (ngx_init_signals(cycle->log) != NGX_OK) {
         return 1;
     }
 
+    /* tell-tale that this code has been executed */
+    child_pid--;
+
     if (!ngx_inherited && ccf->daemon) {
-        if (ngx_daemon(cycle->log) != NGX_OK) {
+        child_pid = ngx_daemon(cycle->log);
+        if (child_pid == NGX_ERROR) {
             return 1;
         }
 
@@ -358,8 +365,19 @@ main(int argc, char *const *argv)
 
 #endif
 
-    if (ngx_create_pidfile(&ccf->pid, cycle->log) != NGX_OK) {
-        return 1;
+    /* If ngx_daemon() returned the child's PID in the parent process
+     * after the fork() set ngx_pid to the child_pid, which gets
+     * written to the PID file, then exit.
+     * For NGX_WIN32 always write the PID file
+     * For others, only write it from the parent process */
+    if (child_pid < NGX_OK || child_pid > NGX_OK) {
+	ngx_pid = child_pid > NGX_OK ? child_pid : ngx_pid;
+        if (ngx_create_pidfile(&ccf->pid, cycle->log) != NGX_OK) {
+            return 1;
+	}
+    }
+    if (child_pid > NGX_OK) {
+        exit(0);
     }
 
     if (ngx_log_redirect_stderr(cycle) != NGX_OK) {
diff --git a/src/os/unix/ngx_daemon.c b/src/os/unix/ngx_daemon.c
index 385c49b6..3719854c 100644
--- a/src/os/unix/ngx_daemon.c
+++ b/src/os/unix/ngx_daemon.c
@@ -7,14 +7,17 @@
 
 #include <ngx_config.h>
 #include <ngx_core.h>
+#include <unistd.h>
 
 
 ngx_int_t
 ngx_daemon(ngx_log_t *log)
 {
     int  fd;
+    /* retain the return value for passing back to caller */
+    pid_t pid_child = fork();
 
-    switch (fork()) {
+    switch (pid_child) {
     case -1:
         ngx_log_error(NGX_LOG_EMERG, log, ngx_errno, "fork() failed");
         return NGX_ERROR;
@@ -23,7 +26,8 @@ ngx_daemon(ngx_log_t *log)
         break;
 
     default:
-        exit(0);
+        /* let caller do the exit() */
+        return pid_child;
     }
 
     ngx_parent = ngx_pid;