[PATCH] Fixed segfault if regex studies list allocation fails

[Maxim Dounin]

# HG changeset patch
# User Maxim Dounin <mdounin at mdounin.ru>
# Date 1681703207 -10800
#      Mon Apr 17 06:46:47 2023 +0300
# Node ID 910ee4cb25e07423a40fa6951d62f74029e7db2d
# Parent  5f1d05a21287ba0290dd3a17ad501595b442a194
Fixed segfault if regex studies list allocation fails.

The rcf->studies list is unconditionally accessed by ngx_regex_cleanup(),
and this used to cause NULL pointer dereference if allocation
failed.  Fix is to set cleanup handler only when allocation succeeds.

diff --git a/src/core/ngx_regex.c b/src/core/ngx_regex.c
--- a/src/core/ngx_regex.c
+++ b/src/core/ngx_regex.c
@@ -732,14 +732,14 @@ ngx_regex_create_conf(ngx_cycle_t *cycle
         return NULL;
     }
 
-    cln->handler = ngx_regex_cleanup;
-    cln->data = rcf;
-
     rcf->studies = ngx_list_create(cycle->pool, 8, sizeof(ngx_regex_elt_t));
     if (rcf->studies == NULL) {
         return NULL;
     }
 
+    cln->handler = ngx_regex_cleanup;
+    cln->data = rcf;
+
     ngx_regex_studies = rcf->studies;
 
     return rcf;