bugfix: ngx.req.set_header: skips setting multi-value headers for bad requests to avoid segfaults.

When setting a multi-value header during bad requests, the value isn't
added into the header's array. Despite failing to be set, the size of the
array is still incremented. Later, if Nginx attempts to iterate over the
array, a segfault will occur.

e21d9b5 established a pattern of silently ignoring the header being set.
I've moved the check for a bad request into `ngx_http_lua_set_input_header`
so that setting a header value is ignored for both types of headers.

Signed-off-by: Yichun Zhang (agentzh) <agentzh@gmail.com>

Author: Emil Stolarsky

src/ngx_http_lua_headers_in.c

@@ -263,11 +263,6 @@ ngx_http_set_header_helper(ngx_http_request_t *r, ngx_http_lua_header_val_t *hv,
 
 new_header:
 
-    if (r->headers_in.headers.last == NULL) {
-        /* must be 400 bad request */
-        return NGX_OK;
-    }
-
     h = ngx_list_push(&r->headers_in.headers);
 
     if (h == NULL) {
@@ -698,6 +693,11 @@ ngx_http_lua_set_input_header(ngx_http_request_t *r, ngx_str_t key,
     }
 #endif
 
+    if (r->headers_out.status == 400 || r->headers_in.headers.last == NULL) {
+        /* must be a 400 Bad Request */
+        return NGX_OK;
+    }
+
     return hv.handler(r, &hv, &value);
 }
 

t/028-req-header.t

@@ -8,7 +8,7 @@ use Test::Nginx::Socket::Lua;
 
 repeat_each(2);
 
-plan tests => repeat_each() * (2 * blocks() + 30);
+plan tests => repeat_each() * (2 * blocks() + 31);
 
 #no_diff();
 #no_long_string();
@@ -1622,3 +1622,24 @@ ok
 --- no_error_log
 [error]
 --- no_check_leak
+
+
+
+=== TEST 54: for bad requests causing segfaults when setting & getting multi-value headers
+--- config
+    error_page 400 = /err;
+
+    location = /err {
+        content_by_lua_block {
+            ngx.req.set_header("Cookie", "foo=bar")
+            local test = ngx.var.cookie_bar
+
+            ngx.say("ok")
+        }
+    }
+--- raw_request
+GeT / HTTP/1.1
+--- response_body
+ok
+--- no_error_log
+[error]