HTTP/2: avoid left-shifting signed integer into the sign bit. On non-aligned platforms, properly cast argument before left-shifting it in ngx_http_v2_parse_uint32 that is used with u_char. Otherwise it propagates to int to hold the value and can step over the sign bit. Usually, on known compilers, this results in negation. Furthermore, a subsequent store into a wider type, that is ngx_uint_t on 64-bit platforms, results in sign-extension. In practice, this can be observed in debug log as a very large exclusive bit value, when client sent PRIORITY frame with exclusive bit set: : *14 http2 PRIORITY frame sid:5 on 1 excl:8589934591 weight:17 Found with UndefinedBehaviorSanitizer.

--- a/src/http/v2/ngx_http_v2.h
+++ b/src/http/v2/ngx_http_v2.h
@@ -298,7 +298,7 @@ size_t ngx_http_v2_huff_encode(u_char *s
 
 #define ngx_http_v2_parse_uint16(p)  ((p)[0] << 8 | (p)[1])
 #define ngx_http_v2_parse_uint32(p)                                           \
-    ((p)[0] << 24 | (p)[1] << 16 | (p)[2] << 8 | (p)[3])
+    ((uint32_t) (p)[0] << 24 | (p)[1] << 16 | (p)[2] << 8 | (p)[3])
 
 #endif