# HG changeset patch
# User Maxim Dounin <mdounin@mdounin.ru>
# Date 1594049777 -10800
# Node ID 7731c710796f3d18f23b35e70dc69a2fc76a05b1
# Parent  c5840ca2063d26e432264ad0b0fe00c0bd94252c
Memcached: protect from too long responses.

If a memcached response was followed by a correct trailer, and then
the NUL character followed by some extra data - this was accepted by
the trailer checking code.  This in turn resulted in ctx->rest underflow
and caused negative size buffer on the next reading from the upstream,
followed by the "negative size buf in writer" alert.

Fix is to always check for too long responses, so a correct trailer cannot
be followed by extra data.

diff --git a/src/http/modules/ngx_http_memcached_module.c b/src/http/modules/ngx_http_memcached_module.c
--- a/src/http/modules/ngx_http_memcached_module.c
+++ b/src/http/modules/ngx_http_memcached_module.c
@@ -485,10 +485,11 @@ ngx_http_memcached_filter(void *data, ss
 
     if (u->length == (ssize_t) ctx->rest) {
 
-        if (ngx_strncmp(b->last,
+        if (bytes > u->length
+            || ngx_strncmp(b->last,
                    ngx_http_memcached_end + NGX_HTTP_MEMCACHED_END - ctx->rest,
                    bytes)
-            != 0)
+               != 0)
         {
             ngx_log_error(NGX_LOG_ERR, ctx->request->connection->log, 0,
                           "memcached sent invalid trailer");
@@ -540,7 +541,9 @@ ngx_http_memcached_filter(void *data, ss
 
     last += (size_t) (u->length - NGX_HTTP_MEMCACHED_END);
 
-    if (ngx_strncmp(last, ngx_http_memcached_end, b->last - last) != 0) {
+    if (bytes > u->length
+        || ngx_strncmp(last, ngx_http_memcached_end, b->last - last) != 0)
+    {
         ngx_log_error(NGX_LOG_ERR, ctx->request->connection->log, 0,
                       "memcached sent invalid trailer");