From 6c480017ae600b2c90a264a922e041df04dfa785 Mon Sep 17 00:00:00 2001
From: Roland Shoemaker <roland@golang.org>
Date: Wed, 18 Aug 2021 11:49:29 -0700
Subject: [PATCH] [release-branch.go1.16] archive/zip: prevent preallocation check from overflowing

If the indicated directory size in the archive header is so large that
subtracting it from the archive size overflows a uint64, the check that
the indicated number of files in the archive can be effectively
bypassed. Prevent this from happening by checking that the indicated
directory size is less than the size of the archive.

Thanks to the OSS-Fuzz project for discovering this issue and to
Emmanuel Odeke for reporting it.

Fixes #47985
Updates #47801
Fixes CVE-2021-39293

Change-Id: Ifade26b98a40f3b37398ca86bd5252d12394dd24
Reviewed-on: https://go-review.googlesource.com/c/go/+/343434
Trust: Roland Shoemaker <roland@golang.org>
Run-TryBot: Roland Shoemaker <roland@golang.org>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Russ Cox <rsc@golang.org>
(cherry picked from commit bacbc33439b124ffd7392c91a5f5d96eca8c0c0b)
Reviewed-on: https://go-review.googlesource.com/c/go/+/345409
Reviewed-by: Emmanuel Odeke <emmanuel@orijtech.com>
Run-TryBot: Emmanuel Odeke <emmanuel@orijtech.com>
Trust: Cherry Mui <cherryyz@google.com>

Reference:https://go-review.googlesource.com/c/go/+/345409
Conflict:NA
---

diff --git a/src/archive/zip/reader.go b/src/archive/zip/reader.go
index ddef2b7..801d131 100644
--- a/src/archive/zip/reader.go
+++ b/src/archive/zip/reader.go
@@ -105,7 +105,7 @@
 	// indicate it contains up to 1 << 128 - 1 files. Since each file has a
 	// header which will be _at least_ 30 bytes we can safely preallocate
 	// if (data size / 30) >= end.directoryRecords.
-	if (uint64(size)-end.directorySize)/30 >= end.directoryRecords {
+	if end.directorySize < uint64(size) && (uint64(size)-end.directorySize)/30 >= end.directoryRecords {
 		z.File = make([]*File, 0, end.directoryRecords)
 	}
 	z.Comment = end.comment
diff --git a/src/archive/zip/reader_test.go b/src/archive/zip/reader_test.go
index 471be27..99f1334 100644
--- a/src/archive/zip/reader_test.go
+++ b/src/archive/zip/reader_test.go
@@ -1225,3 +1225,21 @@
 		t.Errorf("Archive has unexpected number of files, got %d, want 5", len(r.File))
 	}
 }
+
+func TestCVE202139293(t *testing.T) {
+	// directory size is so large, that the check in Reader.init
+	// overflows when subtracting from the archive size, causing
+	// the pre-allocation check to be bypassed.
+	data := []byte{
+		0x50, 0x4b, 0x06, 0x06, 0x05, 0x06, 0x31, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x50, 0x4b,
+		0x06, 0x07, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x01,
+		0x00, 0x00, 0x50, 0x4b, 0x05, 0x06, 0x00, 0x1a, 0x00, 0x00, 0x00, 0x00, 0x00, 0x50, 0x4b,
+		0x06, 0x07, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x01,
+		0x00, 0x00, 0x00, 0x50, 0x4b, 0x05, 0x06, 0x00, 0x31, 0x00, 0x00, 0x00, 0x00, 0xff, 0xff,
+		0xff, 0x50, 0xfe, 0x00, 0xff, 0x00, 0x3a, 0x00, 0x00, 0x00, 0xff,
+	}
+	_, err := NewReader(bytes.NewReader(data), int64(len(data)))
+	if err != ErrFormat {
+		t.Fatalf("unexpected error, got: %v, want: %v", err, ErrFormat)
+	}
+}
