CVE-2025-40044

In the Linux kernel, the following vulnerability has been resolved:

fs: udf: fix OOB read in lengthAllocDescs handling

When parsing Allocation Extent Descriptor, lengthAllocDescs comes from

on-disk data and must be validated against the block size. Crafted or

corrupted images may set lengthAllocDescs so that the total descriptor

length (sizeof(allocExtDesc) + lengthAllocDescs) exceeds the buffer,

leading udf_update_tag() to call crc_itu_t() on out-of-bounds memory and

trigger a KASAN use-after-free read.

BUG: KASAN: use-after-free in crc_itu_t+0x1d5/0x2b0 lib/crc-itu-t.c:60

Read of size 1 at addr ffff888041e7d000 by task syz-executor317/5309

CPU: 0 UID: 0 PID: 5309 Comm: syz-executor317 Not tainted 6.12.0-rc4-syzkaller-00261-g850925a8133c #0

Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2~bpo12+1 04/01/2014

Call Trace:

<TASK>

__dump_stack lib/dump_stack.c:94 [inline]

dump_stack_lvl+0x241/0x360 lib/dump_stack.c:120

print_address_description mm/kasan/report.c:377 [inline]

print_report+0x169/0x550 mm/kasan/report.c:488

kasan_report+0x143/0x180 mm/kasan/report.c:601

crc_itu_t+0x1d5/0x2b0 lib/crc-itu-t.c:60

udf_update_tag+0x70/0x6a0 fs/udf/misc.c:261

udf_write_aext+0x4d8/0x7b0 fs/udf/inode.c:2179

extent_trunc+0x2f7/0x4a0 fs/udf/truncate.c:46

udf_truncate_tail_extent+0x527/0x7e0 fs/udf/truncate.c:106

udf_release_file+0xc1/0x120 fs/udf/file.c:185

__fput+0x23f/0x880 fs/file_table.c:431

task_work_run+0x24f/0x310 kernel/task_work.c:239

exit_task_work include/linux/task_work.h:43 [inline]

do_exit+0xa2f/0x28e0 kernel/exit.c:939

do_group_exit+0x207/0x2c0 kernel/exit.c:1088

__do_sys_exit_group kernel/exit.c:1099 [inline]

__se_sys_exit_group kernel/exit.c:1097 [inline]

__x64_sys_exit_group+0x3f/0x40 kernel/exit.c:1097

x64_sys_call+0x2634/0x2640 arch/x86/include/generated/asm/syscalls_64.h:232

do_syscall_x64 arch/x86/entry/common.c:52 [inline]

do_syscall_64+0xf3/0x230 arch/x86/entry/common.c:83

entry_SYSCALL_64_after_hwframe+0x77/0x7f

</TASK>

Validate the computed total length against epos->bh->b_size.

Found by Linux Verification Center (linuxtesting.org) with Syzkaller.