[nginx] Stream: fixed processing of zero length UDP packets (ticket #1982).

[Vladimir Homutov]

details:   https://hg.nginx.org/nginx/rev/d127837c714f
branches:  
changeset: 7665:d127837c714f
user:      Vladimir Homutov <vl at nginx.com>
date:      Mon Jun 08 11:40:34 2020 +0300
description:
Stream: fixed processing of zero length UDP packets (ticket #1982).

diffstat:

 src/os/unix/ngx_udp_sendmsg_chain.c         |  7 +++++++
 src/stream/ngx_stream_proxy_module.c        |  3 ++-
 src/stream/ngx_stream_write_filter_module.c |  3 ++-
 3 files changed, 11 insertions(+), 2 deletions(-)

diffs (50 lines):

diff -r 699f6e55bbb4 -r d127837c714f src/os/unix/ngx_udp_sendmsg_chain.c
--- a/src/os/unix/ngx_udp_sendmsg_chain.c	Wed Jun 03 19:11:32 2020 +0300
+++ b/src/os/unix/ngx_udp_sendmsg_chain.c	Mon Jun 08 11:40:34 2020 +0300
@@ -189,6 +189,13 @@ ngx_udp_output_chain_to_iovec(ngx_iovec_
         return cl;
     }
 
+    /* zero-sized datagram; pretend to have at least 1 iov */
+    if (n == 0) {
+        iov = &vec->iovs[n++];
+        iov->iov_base = NULL;
+        iov->iov_len = 0;
+    }
+
     vec->count = n;
     vec->size = total;
 
diff -r 699f6e55bbb4 -r d127837c714f src/stream/ngx_stream_proxy_module.c
--- a/src/stream/ngx_stream_proxy_module.c	Wed Jun 03 19:11:32 2020 +0300
+++ b/src/stream/ngx_stream_proxy_module.c	Mon Jun 08 11:40:34 2020 +0300
@@ -839,7 +839,7 @@ ngx_stream_proxy_init_upstream(ngx_strea
         u->upstream_buf.last = p;
     }
 
-    if (c->buffer && c->buffer->pos < c->buffer->last) {
+    if (c->buffer && c->buffer->pos <= c->buffer->last) {
         ngx_log_debug1(NGX_LOG_DEBUG_STREAM, c->log, 0,
                        "stream proxy add preread buffer: %uz",
                        c->buffer->last - c->buffer->pos);
@@ -853,6 +853,7 @@ ngx_stream_proxy_init_upstream(ngx_strea
         *cl->buf = *c->buffer;
 
         cl->buf->tag = (ngx_buf_tag_t) &ngx_stream_proxy_module;
+        cl->buf->temporary = (cl->buf->pos == cl->buf->last) ? 0 : 1;
         cl->buf->flush = 1;
 
         cl->next = u->upstream_out;
diff -r 699f6e55bbb4 -r d127837c714f src/stream/ngx_stream_write_filter_module.c
--- a/src/stream/ngx_stream_write_filter_module.c	Wed Jun 03 19:11:32 2020 +0300
+++ b/src/stream/ngx_stream_write_filter_module.c	Mon Jun 08 11:40:34 2020 +0300
@@ -234,7 +234,8 @@ ngx_stream_write_filter(ngx_stream_sessi
 
     if (size == 0
         && !(c->buffered & NGX_LOWLEVEL_BUFFERED)
-        && !(last && c->need_last_buf))
+        && !(last && c->need_last_buf)
+        && !(c->type == SOCK_DGRAM && flush))
     {
         if (last || flush || sync) {
             for (cl = *out; cl; /* void */) {