http: unset F_CHUNKED on new Transfer-Encoding

Duplicate `Transfer-Encoding` header should be a treated as a single,
but with original header values concatenated with a comma separator. In
the light of this, even if the past `Transfer-Encoding` ended with
`chunked`, we should be not let the `F_CHUNKED` to leak into the next
header, because mere presence of another header indicates that `chunked`
is not the last transfer-encoding token.

CVE-ID: CVE-2020-8287
Refs: nodejs-private/llhttp-private#3
Refs: https://hackerone.com/bugs?report_id=1002188&subject=nodejs
PR-URL: nodejs-private/node-private#228
Reviewed-By: Fedor Indutny <fedor.indutny@gmail.com>
Reviewed-By: Rich Trott <rtrott@gmail.com>

deps/llhttp/src/llhttp.c

@@ -813,6 +813,14 @@ int llhttp__internal__c_or_flags_16(
   return 0;
 }
 
+int llhttp__internal__c_and_flags(
+    llhttp__internal_t* state,
+    const unsigned char* p,
+    const unsigned char* endp) {
+  state->flags &= -9;
+  return 0;
+}
+
 int llhttp__internal__c_update_header_state_7(
     llhttp__internal_t* state,
     const unsigned char* p,
@@ -5974,10 +5982,18 @@ static llparse_state_t llhttp__internal__run(
     /* UNREACHABLE */;
     abort();
   }
+  s_n_llhttp__internal__n_invoke_and_flags: {
+    switch (llhttp__internal__c_and_flags(state, p, endp)) {
+      default:
+        goto s_n_llhttp__internal__n_header_value_te_chunked;
+    }
+    /* UNREACHABLE */;
+    abort();
+  }
   s_n_llhttp__internal__n_invoke_or_flags_16: {
     switch (llhttp__internal__c_or_flags_16(state, p, endp)) {
       default:
-        goto s_n_llhttp__internal__n_header_value_te_chunked;
+        goto s_n_llhttp__internal__n_invoke_and_flags;
     }
     /* UNREACHABLE */;
     abort();
@@ -7625,6 +7641,14 @@ int llhttp__internal__c_or_flags_16(
   return 0;
 }
 
+int llhttp__internal__c_and_flags(
+    llhttp__internal_t* state,
+    const unsigned char* p,
+    const unsigned char* endp) {
+  state->flags &= -9;
+  return 0;
+}
+
 int llhttp__internal__c_update_header_state_7(
     llhttp__internal_t* state,
     const unsigned char* p,
@@ -12522,10 +12546,18 @@ static llparse_state_t llhttp__internal__run(
     /* UNREACHABLE */;
     abort();
   }
+  s_n_llhttp__internal__n_invoke_and_flags: {
+    switch (llhttp__internal__c_and_flags(state, p, endp)) {
+      default:
+        goto s_n_llhttp__internal__n_header_value_te_chunked;
+    }
+    /* UNREACHABLE */;
+    abort();
+  }
   s_n_llhttp__internal__n_invoke_or_flags_16: {
     switch (llhttp__internal__c_or_flags_16(state, p, endp)) {
       default:
-        goto s_n_llhttp__internal__n_header_value_te_chunked;
+        goto s_n_llhttp__internal__n_invoke_and_flags;
     }
     /* UNREACHABLE */;
     abort();