[nginx] Core: added realpath() checking when testing PID files.

[Maxim Dounin]

details:   http://freenginx.org/hg/nginx/rev/4eb02e5ddb48
branches:  
changeset: 9269:4eb02e5ddb48
user:      Maxim Dounin <mdounin at mdounin.ru>
date:      Mon May 13 06:13:12 2024 +0300
description:
Core: added realpath() checking when testing PID files.

This ensures that if the PID file path is changed, yet resolves to the
same file via symbolic links, trying to recreate the PID file won't
remove it.  In particular, this resolves issues as observed on Linux
systems with "/var/run/nginx.pid" changed to "/run/nginx.pid".

diffstat:

 src/core/ngx_cycle.c |  56 +++++++++++++++++++++++++++++++++++++++++++++++++--
 1 files changed, 53 insertions(+), 3 deletions(-)

diffs (80 lines):

diff --git a/src/core/ngx_cycle.c b/src/core/ngx_cycle.c
--- a/src/core/ngx_cycle.c
+++ b/src/core/ngx_cycle.c
@@ -13,6 +13,8 @@
 static void ngx_destroy_cycle_pools(ngx_conf_t *conf);
 static ngx_int_t ngx_init_zone_pool(ngx_cycle_t *cycle,
     ngx_shm_zone_t *shm_zone);
+static ngx_int_t ngx_pidfile_changed(ngx_str_t *name1, ngx_str_t *name2,
+    ngx_log_t *log);
 static ngx_int_t ngx_test_lockfile(u_char *file, ngx_log_t *log);
 static void ngx_clean_old_cycles(ngx_event_t *ev);
 static void ngx_shutdown_timer_handler(ngx_event_t *ev);
@@ -332,9 +334,9 @@ ngx_init_cycle(ngx_cycle_t *old_cycle)
 
         old_ccf = (ngx_core_conf_t *) ngx_get_conf(old_cycle->conf_ctx,
                                                    ngx_core_module);
-        if (ccf->pid.len != old_ccf->pid.len
-            || ngx_strcmp(ccf->pid.data, old_ccf->pid.data) != 0)
-        {
+
+        if (ngx_pidfile_changed(&ccf->pid, &old_ccf->pid, log)) {
+
             /* new pid file name */
 
             if (ngx_create_pidfile(&ccf->pid, log) != NGX_OK) {
@@ -1087,6 +1089,54 @@ ngx_delete_pidfile(ngx_cycle_t *cycle)
 }
 
 
+static ngx_int_t
+ngx_pidfile_changed(ngx_str_t *name1, ngx_str_t *name2, ngx_log_t *log)
+{
+    u_char     *real1, *real2;
+    ngx_int_t   rc;
+
+    if (name1->len == name2->len
+        && ngx_strcmp(name1->data, name2->data) == 0)
+    {
+        return 0;
+    }
+
+    rc = 1;
+    real1 = NULL;
+    real2 = NULL;
+
+    real1 = ngx_realpath(name1->data, NULL);
+
+    if (real1 == NULL) {
+        ngx_log_debug1(NGX_LOG_DEBUG_CORE, log, ngx_errno,
+                       ngx_realpath_n " \"%s\" failed", name1->data);
+        goto done;
+    }
+
+    real2 = ngx_realpath(name2->data, NULL);
+
+    if (real2 == NULL) {
+        ngx_log_debug1(NGX_LOG_DEBUG_CORE, log, ngx_errno,
+                       ngx_realpath_n " \"%s\" failed", name2->data);
+        goto done;
+    }
+
+    rc = ngx_strcmp(real1, real2);
+
+done:
+
+    if (real1 && real1 != name1->data) {
+        ngx_free(real1);
+    }
+
+    if (real2 && real2 != name2->data) {
+        ngx_free(real2);
+    }
+
+    return rc;
+}
+
+
 ngx_int_t
 ngx_signal_process(ngx_cycle_t *cycle, char *sig)
 {