From b835b571846abb13b995498e7ee36fe0f4aaa3bf Mon Sep 17 00:00:00 2001 From: Maxim Dounin Date: Mon, 6 Jul 2020 18:36:17 +0300 Subject: [PATCH] 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. --- src/http/modules/ngx_http_memcached_module.c | 9 ++++++--- 1 file 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");