From 57c9ecf43f1ae0211367d8ba79540e3a5d288d34 Mon Sep 17 00:00:00 2001
From: Willy Tarreau <w@1wt.eu>
Date: Mon, 31 Dec 2018 07:41:24 +0100
Subject: BUG/CRITICAL: mux-h2: re-check the frame length when PRIORITY is used
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Tim Düsterhus reported a possible crash in the H2 HEADERS frame decoder
when the PRIORITY flag is present. A check is missing to ensure the 5
extra bytes needed with this flag are actually part of the frame. As per
RFC7540#4.2, let's return a connection error with code FRAME_SIZE_ERROR.

Many thanks to Tim for responsibly reporting this issue with a working
config and reproducer. This issue was assigned CVE-2018-20615.

This fix must be backported to 1.9 and 1.8.
---
 src/mux_h2.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/src/mux_h2.c b/src/mux_h2.c
index 5803a84ff..a67bbb049 100644
--- a/src/mux_h2.c
+++ b/src/mux_h2.c
@@ -3297,6 +3297,11 @@ next_frame:
 			goto fail;
 		}
 
+		if (flen < 5) {
+			h2c_error(h2c, H2_ERR_FRAME_SIZE_ERROR);
+			goto fail;
+		}
+
 		hdrs += 5; // stream dep = 4, weight = 1
 		flen -= 5;
 	}
-- 
2.20.1