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
index 775bd7e81104ae85f7b5a0db905f7c1ee98ed5a3..c82df6e33738bbd6ac1dd97a8012d195fea7fa30 100644 (file)
--- 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");