From 23fff3442de38877c556f3cda19f3cccef255f7a Mon Sep 17 00:00:00 2001
From: Ryan Liptak <squeek502@hotmail.com>
Date: Fri, 8 Aug 2025 01:37:59 -0700
Subject: [PATCH] flate: Handle invalid block type

Fixes `panic: invalid enum value` when the type bits had the u2 value of 3.

Contributes towards #24741
---
 lib/std/compress/flate/Decompress.zig | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/lib/std/compress/flate/Decompress.zig b/lib/std/compress/flate/Decompress.zig
index a4bb4f291d..07e35b60b5 100644
--- a/lib/std/compress/flate/Decompress.zig
+++ b/lib/std/compress/flate/Decompress.zig
@@ -31,6 +31,7 @@ const BlockType = enum(u2) {
     stored = 0,
     fixed = 1,
     dynamic = 2,
+    invalid = 3,
 };
 
 const State = union(enum) {
@@ -49,6 +50,7 @@ pub const Error = Container.Error || error{
     InvalidCode,
     InvalidMatch,
     WrongStoredBlockNlen,
+    InvalidBlockType,
     InvalidDynamicBlockHeader,
     ReadFailed,
     OversubscribedHuffmanTree,
@@ -360,6 +362,7 @@ fn streamInner(d: *Decompress, w: *Writer, limit: std.Io.Limit) (Error || Reader
 
                     continue :sw .dynamic_block;
                 },
+                .invalid => return error.InvalidBlockType,
             }
         },
         .stored_block => |remaining_len| {
@@ -1141,6 +1144,10 @@ test "puff09" {
     try testDecompress(.raw, @embedFile("testdata/fuzz/puff09.input"), "P");
 }
 
+test "invalid block type" {
+    try testFailure(.raw, &[_]u8{0b110}, error.InvalidBlockType);
+}
+
 test "bug 18966" {
     try testDecompress(
         .gzip,