[patch 3/9] lz4: fix LZ4_decompress_safe_partial read out of bound

[Andrew Morton <akpm@linux-foundation.org>]

From: Guo Xuenan <guoxuenan@huawei.com>
Subject: 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.

In some extreme corner cases when compressed data is suitably
corrupted, UAF will occur.  As reported by KASAN [1],
LZ4_decompress_safe_partial may lead to read out of bound problem
during decoding.  lz4 upstream has fixed it [2] and this issue has been
disscussed here [3] before.

current decompression routine was ported from lz4 v1.8.3, bumping lib/lz4
to v1.9.+ is certainly a huge work to be done later, so, we'd better fix
it first.

[1] https://lore.kernel.org/all/000000000000830d1205cf7f0477@google.com/
[2] https://github.com/lz4/lz4/commit/c5d6f8a8be3927c0bec91bcc58667a6cfad244ad#
[3] https://lore.kernel.org/all/CC666AE8-4CA4-4951-B6FB-A2EFDE3AC03B@fb.com/

Link: https://lkml.kernel.org/r/20211111105048.2006070-1-guoxuenan@huawei.com
Reported-by: syzbot+63d688f1d899c588fb71@syzkaller.appspotmail.com
Signed-off-by: Guo Xuenan <guoxuenan@huawei.com>
Reviewed-by: Nick Terrell <terrelln@fb.com>
Acked-by: Gao Xiang <hsiangkao@linux.alibaba.com>
Cc: Yann Collet <cyan@fb.com>
Cc: Chengyang Fan <cy.fan@huawei.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 lib/lz4/lz4_decompress.c |    8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

--- a/lib/lz4/lz4_decompress.c~lz4-fix-lz4_decompress_safe_partial-read-out-of-bound
+++ a/lib/lz4/lz4_decompress.c
@@ -271,8 +271,12 @@ static FORCE_INLINE int LZ4_decompress_g
 			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 */
_