From 165be368c20e0a1184d5fd2cede0cd0920f233cc Mon Sep 17 00:00:00 2001
From: Klaus Post <klauspost@gmail.com>
Date: Wed, 6 Mar 2024 11:38:00 +0100
Subject: [PATCH] zstd: Reject blocks where reserved values are not 0 (#885)

ref: https://github.com/facebook/zstd/issues/3821
---
 zstd/blockdec.go | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/zstd/blockdec.go b/zstd/blockdec.go
index 9f17ce601f..03744fbc76 100644
--- a/zstd/blockdec.go
+++ b/zstd/blockdec.go
@@ -554,6 +554,9 @@ func (b *blockDec) prepareSequences(in []byte, hist *history) (err error) {
 		if debugDecoder {
 			printf("Compression modes: 0b%b", compMode)
 		}
+		if compMode&3 != 0 {
+			return errors.New("corrupt block: reserved bits not zero")
+		}
 		for i := uint(0); i < 3; i++ {
 			mode := seqCompMode((compMode >> (6 - i*2)) & 3)
 			if debugDecoder {