Re: UBSAN array-index-out-of-bounds in read_blocklist

On 08/04/2024 01:56, Ubisectech Sirius wrote:

Hello.
We are Ubisectech Sirius Team, the vulnerability lab of China ValiantSec. Recently, our team has discovered a issue in Linux kernel 6.8. Attached to the email were a PoC file of the issue.

Hello,

I have found the cause of the problem and fixed it.

A patch will be sent to the LKML shortly.

Thanks

Phillip

Squashfs maintainer.

Stack dump:
------------[ cut here ]------------
UBSAN: array-index-out-of-bounds in fs/squashfs/file.c:256:34
index 4294967295 is out of range for type 'meta_entry [127]'
CPU: 1 PID: 16927 Comm: syz-executor.0 Not tainted 6.8.0 #1
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.15.0-1 04/01/2014
Call Trace:
  <TASK>
  __dump_stack lib/dump_stack.c:88 [inline]
  dump_stack_lvl+0x136/0x150 lib/dump_stack.c:106
  ubsan_epilogue lib/ubsan.c:217 [inline]
  __ubsan_handle_out_of_bounds+0xd5/0x130 lib/ubsan.c:347
  fill_meta_index fs/squashfs/file.c:256 [inline]
  read_blocklist+0x175e/0x1790 fs/squashfs/file.c:333
  squashfs_readahead+0x14fa/0x22d0 fs/squashfs/file.c:591
  read_pages+0x1a2/0xd70 mm/readahead.c:160
  page_cache_ra_unbounded+0x477/0x5f0 mm/readahead.c:269
  do_page_cache_ra mm/readahead.c:299 [inline]
  page_cache_ra_order+0x772/0xa00 mm/readahead.c:544
  do_sync_mmap_readahead mm/filemap.c:3153 [inline]
  filemap_fault+0x1691/0x3390 mm/filemap.c:3245
  __do_fault+0x108/0x490 mm/memory.c:4396
  do_read_fault mm/memory.c:4758 [inline]
  do_fault mm/memory.c:4888 [inline]
  do_pte_missing mm/memory.c:3745 [inline]
  handle_pte_fault mm/memory.c:5164 [inline]
  __handle_mm_fault+0x340a/0x48b0 mm/memory.c:5305
  handle_mm_fault+0x3c2/0xa40 mm/memory.c:5470
  do_user_addr_fault+0x2ed/0x1010 arch/x86/mm/fault.c:1355
  handle_page_fault arch/x86/mm/fault.c:1498 [inline]
  exc_page_fault+0x99/0x180 arch/x86/mm/fault.c:1554
  asm_exc_page_fault+0x26/0x30 arch/x86/include/asm/idtentry.h:570
RIP: 0033:0x7f8446a28202
Code: 48 63 c3 5b c3 0f 1f 00 f3 0f 1e fa 48 89 7c 24 f0 48 89 74 24 e8 48 89 54 24 e0 48 8b 4c 24 f0 48 8b 54 24 e8 48 8b 74 24 e0 <8b> 41 40 23 81 00 01 00 00 f3 0f 6f 06 c1 e0 06 48 01 d0 0f 11 00
RSP: 002b:00007f8447755018 EFLAGS: 00010212
RAX: 00007f8446a281e0 RBX: 00007f8446bcbf80 RCX: 0000000020ff0000
RDX: 0000000000000000 RSI: 0000000020000000 RDI: 0000000020ff0000
RBP: 00007f8446af14a6 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000020ff0000 R11: 0000000020000000 R12: 0000000000000000
R13: 000000000000000b R14: 00007f8446bcbf80 R15: 00007f8447735000
  </TASK>
---[ end trace ]---

Thank you for taking the time to read this email and we look forward to working with you further.