[PATCH] ntfs3: check if more than chunk-size bytes are written

[PATCH] ntfs3: check if more than chunk-size bytes are written

[Andrew Ballance]

#syz test

a incorrectly formatted chunk may decompress into
more than LZNT_CHUNK_SIZE bytes and a index out of bounds
will occur in s_max_off.

Signed-off-by: Andrew Ballance <andrewjballance@gmail.com>
---
 fs/ntfs3/lznt.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/fs/ntfs3/lznt.c b/fs/ntfs3/lznt.c
index 4aae598d6d88..fdc9b2ebf341 100644
--- a/fs/ntfs3/lznt.c
+++ b/fs/ntfs3/lznt.c
@@ -236,6 +236,9 @@ static inline ssize_t decompress_chunk(u8 *unc, u8 *unc_end, const u8 *cmpr,
 
 	/* Do decompression until pointers are inside range. */
 	while (up < unc_end && cmpr < cmpr_end) {
+		// return err if more than LZNT_CHUNK_SIZE bytes are written
+		if (up - unc > LZNT_CHUNK_SIZE)
+			return -EINVAL;
 		/* Correct index */
 		while (unc + s_max_off[index] < up)
 			index += 1;
-- 
2.45.0

Re: [syzbot] [ntfs3?] UBSAN: array-index-out-of-bounds in decompress_lznt

[syzbot]

Hello,

syzbot has tested the proposed patch and the reproducer did not trigger any issue:

Reported-and-tested-by: syzbot+39b2fb0f2638669008ec@syzkaller.appspotmail.com

Tested on:

commit:         1b294a1f Merge tag 'net-next-6.10' of git://git.kernel..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=15998648980000
kernel config:  https://syzkaller.appspot.com/x/.config?x=c0cd0c5dbf8ea592
dashboard link: https://syzkaller.appspot.com/bug?extid=39b2fb0f2638669008ec
compiler:       Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40
patch:          https://syzkaller.appspot.com/x/patch.diff?x=115b78f0980000

Note: testing is done by a robot and is best-effort only.