# HG changeset patch
# User Sergey Kandaurov <pluknet@nginx.com>
# Date 1682954165 -14400
# Node ID b71e69247483631bd8fc79a47cc32b762625b1fb
# Parent  77d5c662f3d9d9b90425128109d3369c30ef5f07
Variables: avoid possible buffer overrun with some "$sent_http_*".

The existing logic to evaluate multi header "$sent_http_*" variables,
such as $sent_http_cache_control, as previously introduced in 1.23.0,
doesn't take into account that one or more elements can be cleared,
yet still present in a linked list, pointed to by the next field.
Such elements don't contribute to the resulting variable length, an
attempt to append a separator for them ends up in out of bounds write.

This is not possible with standard modules, though at least one third
party module is known to override multi header values this way, so it
makes sense to harden the logic.

The fix restores a generic boundary check.

diff --git a/src/http/ngx_http_variables.c b/src/http/ngx_http_variables.c
--- a/src/http/ngx_http_variables.c
+++ b/src/http/ngx_http_variables.c
@@ -828,7 +828,7 @@ ngx_http_variable_headers_internal(ngx_h
     ngx_http_variable_value_t *v, uintptr_t data, u_char sep)
 {
     size_t            len;
-    u_char           *p;
+    u_char           *p, *end;
     ngx_table_elt_t  *h, *th;
 
     h = *(ngx_table_elt_t **) ((char *) r + data);
@@ -870,6 +870,8 @@ ngx_http_variable_headers_internal(ngx_h
     v->len = len;
     v->data = p;
 
+    end = p + len;
+
     for (th = h; th; th = th->next) {
 
         if (th->hash == 0) {
@@ -878,7 +880,7 @@ ngx_http_variable_headers_internal(ngx_h
 
         p = ngx_copy(p, th->value.data, th->value.len);
 
-        if (th->next == NULL) {
+        if (p == end) {
             break;
         }