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.

1 files changed, 6 insertions, 3 deletions

diff --git a/src/http/modules/ngx_http_memcached_module.c b/src/http/modules/ngx_http_memcached_module.c
index 775bd7e81..c82df6e33 100644
--- 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, ssize_t bytes)
 
     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, ssize_t bytes)
 
     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");