Core: fixed environment on exit.

On exit environment allocated from a pool is no longer available, leading
to a segmentation fault if, for example, a library tries to use it from
an atexit() handler.

Fix is to allocate environment via ngx_alloc() instead, and explicitly
free it using a pool cleanup handler if it's no longer used (e.g., on
configuration reload).

src/core/nginx.c

@@ -12,6 +12,7 @@
 
 static void ngx_show_version_info(void);
 static ngx_int_t ngx_add_inherited_sockets(ngx_cycle_t *cycle);
+static void ngx_cleanup_environment(void *data);
 static ngx_int_t ngx_get_options(int argc, char *const *argv);
 static ngx_int_t ngx_process_options(ngx_cycle_t *cycle);
 static ngx_int_t ngx_save_argv(ngx_cycle_t *cycle, int argc, char *const *argv);
@@ -495,10 +496,11 @@ ngx_add_inherited_sockets(ngx_cycle_t *cycle)
 char **
 ngx_set_environment(ngx_cycle_t *cycle, ngx_uint_t *last)
 {
-    char             **p, **env;
-    ngx_str_t         *var;
-    ngx_uint_t         i, n;
-    ngx_core_conf_t   *ccf;
+    char                **p, **env;
+    ngx_str_t            *var;
+    ngx_uint_t            i, n;
+    ngx_core_conf_t      *ccf;
+    ngx_pool_cleanup_t   *cln;
 
     ccf = (ngx_core_conf_t *) ngx_get_conf(cycle->conf_ctx, ngx_core_module);
 
@@ -550,14 +552,25 @@ tz_found:
 
     if (last) {
         env = ngx_alloc((*last + n + 1) * sizeof(char *), cycle->log);
+        if (env == NULL) {
+            return NULL;
+        }
+
         *last = n;
 
     } else {
-        env = ngx_palloc(cycle->pool, (n + 1) * sizeof(char *));
-    }
+        cln = ngx_pool_cleanup_add(cycle->pool, 0);
+        if (cln == NULL) {
+            return NULL;
+        }
 
-    if (env == NULL) {
-        return NULL;
+        env = ngx_alloc((n + 1) * sizeof(char *), cycle->log);
+        if (env == NULL) {
+            return NULL;
+        }
+
+        cln->handler = ngx_cleanup_environment;
+        cln->data = env;
     }
 
     n = 0;
@@ -591,6 +604,25 @@ tz_found:
 }
 
 
+static void
+ngx_cleanup_environment(void *data)
+{
+    char  **env = data;
+
+    if (environ == env) {
+
+        /*
+         * if the environment is still used, as it happens on exit,
+         * the only option is to leak it
+         */
+
+        return;
+    }
+
+    ngx_free(env);
+}
+
+
 ngx_pid_t
 ngx_exec_new_binary(ngx_cycle_t *cycle, char *const *argv)
 {