[PATCH] SSI: ensure context of main request exists for subrequest using SSI

[Ciel]

# HG changeset patch
# User Ciel Zhao <i at ciel.dev>
# Date 1667411069 -28800
#      Thu Nov 03 01:44:29 2022 +0800
# Node ID 85141e004b5af89a9d443bc0084a34291193567a
# Parent  1ae25660c0c76edef14121ca64362f28b9d57a70
SSI: ensure context of main request exists for subrequest using SSI

As the SSI parser always uses the context from the main request for storing
variables and blocks, that context should always exist for subrequests using
SSI, even though the main request does not necessarily have SSI enabled.

However, `ngx_http_get_module_ctx(r->main, ...)` is getting NULL in such cases,
resulting in the worker crashing SIGSEGV when accessing its attributes.

This patch checks the context of the main request after initializing the context
for subrequests, and creates one if not exists.

diff -r 1ae25660c0c7 -r 85141e004b5a src/http/modules/ngx_http_ssi_filter_module.c
--- a/src/http/modules/ngx_http_ssi_filter_module.c  Wed Oct 19 10:56:21 2022 +0300
+++ b/src/http/modules/ngx_http_ssi_filter_module.c  Thu Nov 03 01:44:29 2022 +0800
@@ -329,7 +329,7 @@
 static ngx_int_t
 ngx_http_ssi_header_filter(ngx_http_request_t *r)
 {
-    ngx_http_ssi_ctx_t       *ctx;
+    ngx_http_ssi_ctx_t       *ctx, *mctx;
     ngx_http_ssi_loc_conf_t  *slcf;
 
     slcf = ngx_http_get_module_loc_conf(r, ngx_http_ssi_filter_module);
@@ -348,6 +348,16 @@
 
     ngx_http_set_ctx(r, ctx, ngx_http_ssi_filter_module);
 
+    mctx = ngx_http_get_module_ctx(r->main, ngx_http_ssi_filter_module);
+    if (mctx == NULL && r != r->main) {
+        mctx = ngx_pcalloc(r->main->pool, sizeof(ngx_http_ssi_ctx_t));
+        if (mctx == NULL) {
+            return NGX_ERROR;
+        }
+
+        ngx_http_set_ctx(r->main, mctx, ngx_http_ssi_filter_module);
+    }
+
 
     ctx->value_len = slcf->value_len;
     ctx->last_out = &ctx->out;
@@ -403,8 +413,12 @@
     ngx_str_t                 *params[NGX_HTTP_SSI_MAX_PARAMS + 1];
 
     ctx = ngx_http_get_module_ctx(r, ngx_http_ssi_filter_module);
+    slcf = ngx_http_get_module_loc_conf(r, ngx_http_ssi_filter_module);
 
     if (ctx == NULL
+        || !slcf->enable
+        || r->headers_out.content_length_n == 0
+        || ngx_http_test_content_type(r, &slcf->types) == NULL
         || (in == NULL
             && ctx->buf == NULL
             && ctx->in == NULL
@@ -450,8 +464,6 @@
         }
     }
 
-    slcf = ngx_http_get_module_loc_conf(r, ngx_http_ssi_filter_module);
-
     while (ctx->in || ctx->buf) {
 
         if (ctx->buf == NULL) {