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>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/lib/lz4/lz4_decompress.c b/lib/lz4/lz4_decompress.c
index 926f4823d5eac832a5b6e78c5c08228d400ca5ad..fd1728d94babb28f997bf10c2b2180ae5cdec2c0 100644 (file)
--- 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 */