HTTP/2: extended guard for NULL buffer and zero length.

In addition to moving memcpy() under the length condition in 15bf6d8cc,
which addressed a reported UB due to string function conventions, this
is repeated for advancing an input buffer, to make the resulting code
more clean and readable.

Additionally, although considered harmless for both string functions and
additive operators, as previously discussed in GitHub PR 866, this fixes
the main source of annoying sanitizer reports in the module.

Prodded by UndefinedBehaviorSanitizer (pointer-overflow).

diff --git a/src/http/v2/ngx_http_v2.c b/src/http/v2/ngx_http_v2.c
index fe9ee5a881e29c82ca9a16de3e66e56491f16533..4bfee589ad49699df866cb03f8c3af619020cba1 100644 (file)
--- a/src/http/v2/ngx_http_v2.c
+++ b/src/http/v2/ngx_http_v2.c
@@ -4113,15 +4113,14 @@ ngx_http_v2_process_request_body(ngx_http_request_t *r, u_char *pos,
                 n = size;
             }
 
-            if (n > 0) {
-                rb->buf->last = ngx_cpymem(rb->buf->last, pos, n);
-            }
-
             ngx_log_debug1(NGX_LOG_DEBUG_HTTP, fc->log, 0,
                            "http2 request body recv %uz", n);
 
-            pos += n;
-            size -= n;
+            if (n > 0) {
+                rb->buf->last = ngx_cpymem(rb->buf->last, pos, n);
+                pos += n;
+                size -= n;
+            }
 
             if (size == 0 && last) {
                 rb->rest = 0;