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

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

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit:    f4345f05c0df Merge tag 'block-6.9-20240510' of git://git.k..
git tree:       upstream
console+strace: https://syzkaller.appspot.com/x/log.txt?x=15035598980000
kernel config:  https://syzkaller.appspot.com/x/.config?x=9d7ea7de0cb32587
dashboard link: https://syzkaller.appspot.com/bug?extid=39b2fb0f2638669008ec
compiler:       Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=16375db8980000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=16ef17a8980000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/eab3aead3b47/disk-f4345f05.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/64d327c02024/vmlinux-f4345f05.xz
kernel image: https://storage.googleapis.com/syzbot-assets/0191e269a6fd/bzImage-f4345f05.xz
mounted in repro #1: https://storage.googleapis.com/syzbot-assets/293e623536d7/mount_0.gz
mounted in repro #2: https://storage.googleapis.com/syzbot-assets/165c0c1a16ff/mount_1.gz

The issue was bisected to:

commit d68968440b1a75dee05cfac7f368f1aa139e1911
Author: Konstantin Komarov <almaz.alexandrovich@paragon-software.com>
Date:   Mon Jan 29 07:30:09 2024 +0000

    fs/ntfs3: Update inode->i_size after success write into compressed file

bisection log:  https://syzkaller.appspot.com/x/bisect.txt?x=13472020980000
final oops:     https://syzkaller.appspot.com/x/report.txt?x=10c72020980000
console output: https://syzkaller.appspot.com/x/log.txt?x=17472020980000

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+39b2fb0f2638669008ec@syzkaller.appspotmail.com
Fixes: d68968440b1a ("fs/ntfs3: Update inode->i_size after success write into compressed file")

------------[ cut here ]------------
UBSAN: array-index-out-of-bounds in fs/ntfs3/lznt.c:240:16
index 9 is out of range for type 'const size_t[9]' (aka 'const unsigned long[9]')
CPU: 1 PID: 5072 Comm: syz-executor335 Not tainted 6.9.0-rc7-syzkaller-00136-gf4345f05c0df #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 04/02/2024
Call Trace:
 <TASK>
 __dump_stack lib/dump_stack.c:88 [inline]
 dump_stack_lvl+0x241/0x360 lib/dump_stack.c:114
 ubsan_epilogue lib/ubsan.c:231 [inline]
 __ubsan_handle_out_of_bounds+0x121/0x150 lib/ubsan.c:429
 decompress_chunk fs/ntfs3/lznt.c:240 [inline]
 decompress_lznt+0x229/0xd50 fs/ntfs3/lznt.c:387
 ni_read_frame+0x1633/0x1c50 fs/ntfs3/frecord.c:2684
 ni_readpage_cmpr+0x38b/0xa60 fs/ntfs3/frecord.c:2143
 ntfs_read_folio+0x19e/0x210 fs/ntfs3/inode.c:725
 filemap_read_folio+0x1a0/0x790 mm/filemap.c:2331
 filemap_update_page mm/filemap.c:2415 [inline]
 filemap_get_pages+0x15a9/0x2090 mm/filemap.c:2529
 filemap_read+0x457/0xfa0 mm/filemap.c:2601
 __kernel_read+0x5c8/0xab0 fs/read_write.c:434
 integrity_kernel_read+0xb0/0x100 security/integrity/iint.c:28
 ima_calc_file_hash_tfm security/integrity/ima/ima_crypto.c:485 [inline]
 ima_calc_file_shash security/integrity/ima/ima_crypto.c:516 [inline]
 ima_calc_file_hash+0xadb/0x1b30 security/integrity/ima/ima_crypto.c:573
 ima_collect_measurement+0x535/0xa90 security/integrity/ima/ima_api.c:291
 process_measurement+0x13ac/0x1f60 security/integrity/ima/ima_main.c:359
 ima_file_check+0xf2/0x170 security/integrity/ima/ima_main.c:559
 security_file_post_open+0x6d/0xa0 security/security.c:2981
 do_open fs/namei.c:3644 [inline]
 path_openat+0x28b7/0x3240 fs/namei.c:3799
 do_filp_open+0x235/0x490 fs/namei.c:3826
 do_sys_openat2+0x13e/0x1d0 fs/open.c:1406
 do_sys_open fs/open.c:1421 [inline]
 __do_sys_open fs/open.c:1429 [inline]
 __se_sys_open fs/open.c:1425 [inline]
 __x64_sys_open+0x225/0x270 fs/open.c:1425
 do_syscall_x64 arch/x86/entry/common.c:52 [inline]
 do_syscall_64+0xf5/0x240 arch/x86/entry/common.c:83
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7fbd0c2059b9
Code: 28 00 00 00 75 05 48 83 c4 28 c3 e8 61 17 00 00 90 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 b8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007fffa3c72cd8 EFLAGS: 00000246 ORIG_RAX: 0000000000000002
RAX: ffffffffffffffda RBX: 00007fffa3c72ea8 RCX: 00007fbd0c2059b9
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000020000180
RBP: 00007fbd0c298610 R08: 00007fffa3c72ea8 R09: 00007fffa3c72ea8
R10: 00007fffa3c72ea8 R11: 0000000000000246 R12: 0000000000000001
R13: 00007fffa3c72e98 R14: 0000000000000001 R15: 0000000000000001
 </TASK>
---[ end trace ]---


---
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For information about bisection process see: https://goo.gl/tpsmEJ#bisection

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#syz fix: exact-commit-title

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[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.

Re: [syzbot] test

[syzbot]

For archival purposes, forwarding an incoming command email to
linux-kernel@vger.kernel.org, syzkaller-bugs@googlegroups.com.

***

Subject: test
Author: mukattreyee@gmail.com

#syz test:
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master

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

[syzbot]

For archival purposes, forwarding an incoming command email to
linux-kernel@vger.kernel.org, syzkaller-bugs@googlegroups.com.

***

Subject: UBSAN: array-index-out-of-bounds in decompress_lznt
Author: almaz.alexandrovich@paragon-software.com

#syz test: https://github.com/Paragon-Software-Group/linux-ntfs3.git master

Forwarded: [PATCH] ntfs3: fix array-index-out-of-bounds in decompress_lznt

[syzbot]

For archival purposes, forwarding an incoming command email to
linux-kernel@vger.kernel.org, syzkaller-bugs@googlegroups.com.

***

Subject: [PATCH] ntfs3: fix array-index-out-of-bounds in decompress_lznt
Author: tristmd@gmail.com

From: Tristan Madani <tristan@talencesecurity.com>

#syz test: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master


The index correction loop in decompress_chunk() increments the index
variable without checking against the s_max_off[] array size:

    while (unc + s_max_off[index] < up)
        index += 1;

When a crafted NTFS image causes the decompressed output pointer (up) to
advance beyond unc + s_max_off[8] (0x1000), the loop reads s_max_off[9]
which is past the end of the 9-element array, triggering UBSAN:

  UBSAN: array-index-out-of-bounds in fs/ntfs3/lznt.c:243:16
  index 9 is out of range for type 'const size_t[9]'

Commit 9931122d04c6 ("fs/ntfs3: Check if more than chunk-size bytes are
written") partially addressed this by adding a check for up - unc >
LZNT_CHUNK_SIZE before the loop.  However, this relies on the implicit
invariant that LZNT_CHUNK_SIZE equals s_max_off[ARRAY_SIZE(s_max_off)-1],
and the check uses strict greater-than which still allows index to reach
the boundary value in edge cases with concurrent modifications to the
unc_end bound.

Add a direct bounds check on index within the while loop condition to
make the code robust regardless of the relationship between
LZNT_CHUNK_SIZE and s_max_off[] values.  If index reaches the maximum,
break out of the correction loop -- the entry at s_max_off[8] (0x1000)
already covers the full chunk range.

Found by syzbot.

Reported-by: syzbot+39b2fb0f2638669008ec@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=39b2fb0f2638669008ec
Fixes: 522e010b5837 ("fs/ntfs3: Add compression")
Cc: stable@vger.kernel.org
Signed-off-by: Tristan Madani <tristan@talencesecurity.com>
---
 fs/ntfs3/lznt.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/ntfs3/lznt.c b/fs/ntfs3/lznt.c
index XXXXXXX..XXXXXXX 100644
--- a/fs/ntfs3/lznt.c
+++ b/fs/ntfs3/lznt.c
@@ -240,7 +240,7 @@ static inline ssize_t decompress_chunk(u8 *unc, u8 *unc_end, const u8 *cmpr,
 		if (up - unc > LZNT_CHUNK_SIZE)
 			return -EINVAL;
 		/* Correct index */
-		while (unc + s_max_off[index] < up)
+		while (index < ARRAY_SIZE(s_max_off) - 1 && unc + s_max_off[index] < up)
 			index += 1;

 		/* Check the current flag for zero. */
--
2.39.5

Forwarded: Re: [syzbot] KASAN: slab-out-of-bounds in decompress_lznt

[syzbot]

For archival purposes, forwarding an incoming command email to
linux-kernel@vger.kernel.org, syzkaller-bugs@googlegroups.com.

***

Subject: Re: [syzbot] KASAN: slab-out-of-bounds in decompress_lznt
Author: tristmd@gmail.com

#syz test: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master
>From 6cfb2c5508cbe3c057fc4fe83808ef6cf8fc9868 Mon Sep 17 00:00:00 2001
From: Tristan Madani <tristan@talencesecurity.com>
Date: Fri, 17 Apr 2026 16:15:16 +0000
Subject: [PATCH] ntfs3: fix array-index-out-of-bounds in decompress_lznt
decompress_chunk() increments index without checking array bounds,
leading to an out-of-bounds access on s_max_off when processing
corrupted compressed data.
Add an upper bound check on index to prevent the overflow.
Reported-by: syzbot+39b2fb0f2638669008ec@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=39b2fb0f2638669008ec
Signed-off-by: Tristan Madani <tristan@talencesecurity.com>
---
 fs/ntfs3/lznt.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/fs/ntfs3/lznt.c b/fs/ntfs3/lznt.c
index fdc9b2e..f818d97 100644
--- a/fs/ntfs3/lznt.c
+++ b/fs/ntfs3/lznt.c
@@ -240,7 +240,7 @@ static inline ssize_t decompress_chunk(u8 *unc, u8 *unc_end, const u8 *cmpr,
 		if (up - unc > LZNT_CHUNK_SIZE)
 			return -EINVAL;
 		/* Correct index */
-		while (unc + s_max_off[index] < up)
+		while (index < ARRAY_SIZE(s_max_off) - 1 && unc + s_max_off[index] < up)
 			index += 1;
 
 		/* Check the current flag for zero. */
-- 
2.47.3