linux-kernel - [PATCH] lz4: fix LZ4_decompress_safe

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Date:   Thu, 11 Nov 2021 15:17:59 +0800
From:   Guo Xuenan <guoxuenan@...wei.com>
To:     <akpm@...ux-foundation.org>
CC:     <linux-kernel@...r.kernel.org>, <hsiangkao@...hat.com>,
        <terrelln@...com>, <cyan@...com>, <cy.fan@...wei.com>,
        <fangwei1@...wei.com>, <wangli74@...wei.com>,
        <guoxuenan@...wei.com>,
        <syzbot+63d688f1d899c588fb71@...kaller.appspotmail.com>,
        <hsiangkao@...ux.alibaba.com>
Subject: [PATCH] lz4: fix LZ4_decompress_safe_partial read out of bound

When partialDecoding, it is EOF if we've either, filled the output
buffer or can't proceed with reading an offset for following match.

As reported by KASAN[1], LZ4_decompress_safe_partial may lead
to erofs decoding read out of bound. Fortunately, lz4 upstream has
fixed it [2]. current decompression routine was ported from lz4 v1.8.3,
so, we can fix it, before bumping lib/lz4 to v1.9.+.

[1] https://syzkaller.appspot.com/bug?extid=63d688f1d899c588fb71
[2] https://github.com/lz4/lz4/commit/c5d6f8a8be3927c0bec91bcc58667a6cfad244ad#

Reported-by: syzbot+63d688f1d899c588fb71@...kaller.appspotmail.com
Cc: hsiangkao@...ux.alibaba.com
Cc: terrelln@...com
Cc: cyan@...com
Cc: cy.fan@...wei.com
Signed-off-by: Guo Xuenan <guoxuenan@...wei.com>
---
 lib/lz4/lz4_decompress.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/lib/lz4/lz4_decompress.c b/lib/lz4/lz4_decompress.c
index 926f4823d5ea..fd1728d94bab 100644
--- a/lib/lz4/lz4_decompress.c
+++ b/lib/lz4/lz4_decompress.c
@@ -271,8 +271,12 @@ static FORCE_INLINE int LZ4_decompress_generic(
 			ip += length;
 			op += length;
 
-			/* Necessarily EOF, due to parsing restrictions */
-			if (!partialDecoding || (cpy == oend))
+			/* Necessarily EOF when !partialDecoding.
+			 * When partialDecoding, it is EOF if we've either
+			 * filled the output buffer or
+			 * can't proceed with reading an offset for following match.
+			 */
+			if (!partialDecoding || (cpy == oend) || (ip >= (iend - 2)))
 				break;
 		} else {
 			/* may overwrite up to WILDCOPYLENGTH beyond cpy */
-- 
2.31.1