HTTP: uniform checks in ngx_http_alloc_large_header_buffer().

If URI is not fully parsed yet, some pointers are not set.  As a result,
the calculation of "new + (ptr - old)" expression is flawed.

According to C11, 6.5.6 Additive operators, p.9:

: When two pointers are subtracted, both shall point to elements
: of the same array object, or one past the last element of the
: array object

Since "ptr" is not set, subtraction leads to undefined behaviour, because
"ptr" and "old" are not in the same buffer (i.e. array objects).

Prodded by GCC undefined behaviour sanitizer.

1 files changed, 25 insertions, 7 deletions

diff --git a/src/http/ngx_http_request.c b/src/http/ngx_http_request.c
index 058d50286..21738ff4c 100644
--- a/src/http/ngx_http_request.c
+++ b/src/http/ngx_http_request.c
@@ -1718,14 +1718,23 @@ ngx_http_alloc_large_header_buffer(ngx_http_request_t *r,
             r->request_end = new + (r->request_end - old);
         }
 
-        r->method_end = new + (r->method_end - old);
+        if (r->method_end) {
+            r->method_end = new + (r->method_end - old);
+        }
+
+        if (r->uri_start) {
+            r->uri_start = new + (r->uri_start - old);
+        }
 
-        r->uri_start = new + (r->uri_start - old);
-        r->uri_end = new + (r->uri_end - old);
+        if (r->uri_end) {
+            r->uri_end = new + (r->uri_end - old);
+        }
 
         if (r->schema_start) {
             r->schema_start = new + (r->schema_start - old);
-            r->schema_end = new + (r->schema_end - old);
+            if (r->schema_end) {
+                r->schema_end = new + (r->schema_end - old);
+            }
         }
 
         if (r->host_start) {
@@ -1749,9 +1758,18 @@ ngx_http_alloc_large_header_buffer(ngx_http_request_t *r,
 
     } else {
         r->header_name_start = new;
-        r->header_name_end = new + (r->header_name_end - old);
-        r->header_start = new + (r->header_start - old);
-        r->header_end = new + (r->header_end - old);
+
+        if (r->header_name_end) {
+            r->header_name_end = new + (r->header_name_end - old);
+        }
+
+        if (r->header_start) {
+            r->header_start = new + (r->header_start - old);
+        }
+
+        if (r->header_end) {
+            r->header_end = new + (r->header_end - old);
+        }
     }
 
     r->header_in = b;