linux-kernel - [PATCH] fs: udf: fix OOB read in lengthAllocDescs handling

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Message-ID: <20250922131358.745579-1-Sergey.Larshin@kaspersky.com>
Date: Mon, 22 Sep 2025 16:13:58 +0300
From: Larshin Sergey <Sergey.Larshin@...persky.com>
To: Jan Kara <jack@...e.com>
CC: Larshin Sergey <Sergey.Larshin@...persky.com>,
	<linux-kernel@...r.kernel.org>, <lvc-project@...uxtesting.org>,
	<Oleg.Kazakov@...persky.com>,
	<syzbot+8743fca924afed42f93e@...kaller.appspotmail.com>,
	<stable@...r.kernel.org>
Subject: [PATCH] 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.

Reported-by: syzbot+8743fca924afed42f93e@...kaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=8743fca924afed42f93e
Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Cc: stable@...r.kernel.org

Signed-off-by: Larshin Sergey <Sergey.Larshin@...persky.com>
---
 fs/udf/inode.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/fs/udf/inode.c b/fs/udf/inode.c
index f24aa98e6869..a79d73f28aa7 100644
--- a/fs/udf/inode.c
+++ b/fs/udf/inode.c
@@ -2272,6 +2272,9 @@ int udf_current_aext(struct inode *inode, struct extent_position *epos,
 		if (check_add_overflow(sizeof(struct allocExtDesc),
 				le32_to_cpu(header->lengthAllocDescs), &alen))
 			return -1;
+
+		if (alen > epos->bh->b_size)
+			return -1;
 	}
 
 	switch (iinfo->i_alloc_type) {
-- 
2.39.5