CVE-2022-49763

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

ntfs: fix use-after-free in ntfs_attr_find()

Patch series "ntfs: fix bugs about Attribute", v2.

This patchset fixes three bugs relative to Attribute in record:

Patch 1 adds a sanity check to ensure that, attrs_offset field in first

mft record loading from disk is within bounds.

Patch 2 moves the ATTR_RECORD's bounds checking earlier, to avoid

dereferencing ATTR_RECORD before checking this ATTR_RECORD is within

bounds.

Patch 3 adds an overflow checking to avoid possible forever loop in

ntfs_attr_find().

Without patch 1 and patch 2, the kernel triggersa KASAN use-after-free

detection as reported by Syzkaller.

Although one of patch 1 or patch 2 can fix this, we still need both of

them. Because patch 1 fixes the root cause, and patch 2 not only fixes

the direct cause, but also fixes the potential out-of-bounds bug.

This patch (of 3):

Syzkaller reported use-after-free read as follows:

==================================================================

BUG: KASAN: use-after-free in ntfs_attr_find+0xc02/0xce0 fs/ntfs/attrib.c:597

Read of size 2 at addr ffff88807e352009 by task syz-executor153/3607

[...]

Call Trace:

<TASK>

__dump_stack lib/dump_stack.c:88 [inline]

dump_stack_lvl+0xcd/0x134 lib/dump_stack.c:106

print_address_description mm/kasan/report.c:317 [inline]

print_report.cold+0x2ba/0x719 mm/kasan/report.c:433

kasan_report+0xb1/0x1e0 mm/kasan/report.c:495

ntfs_attr_find+0xc02/0xce0 fs/ntfs/attrib.c:597

ntfs_attr_lookup+0x1056/0x2070 fs/ntfs/attrib.c:1193

ntfs_read_inode_mount+0x89a/0x2580 fs/ntfs/inode.c:1845

ntfs_fill_super+0x1799/0x9320 fs/ntfs/super.c:2854

mount_bdev+0x34d/0x410 fs/super.c:1400

legacy_get_tree+0x105/0x220 fs/fs_context.c:610

vfs_get_tree+0x89/0x2f0 fs/super.c:1530

do_new_mount fs/namespace.c:3040 [inline]

path_mount+0x1326/0x1e20 fs/namespace.c:3370

do_mount fs/namespace.c:3383 [inline]

__do_sys_mount fs/namespace.c:3591 [inline]

__se_sys_mount fs/namespace.c:3568 [inline]

__x64_sys_mount+0x27f/0x300 fs/namespace.c:3568

do_syscall_x64 arch/x86/entry/common.c:50 [inline]

do_syscall_64+0x35/0xb0 arch/x86/entry/common.c:80

entry_SYSCALL_64_after_hwframe+0x63/0xcd

[...]

</TASK>

The buggy address belongs to the physical page:

page:ffffea0001f8d400 refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x7e350

head:ffffea0001f8d400 order:3 compound_mapcount:0 compound_pincount:0

flags: 0xfff00000010200(slab|head|node=0|zone=1|lastcpupid=0x7ff)

raw: 00fff00000010200 0000000000000000 dead000000000122 ffff888011842140

raw: 0000000000000000 0000000000040004 00000001ffffffff 0000000000000000

page dumped because: kasan: bad access detected

Memory state around the buggy address:

ffff88807e351f00: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc

ffff88807e351f80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc

>ffff88807e352000: fa fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb

^

ffff88807e352080: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb

ffff88807e352100: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb

==================================================================

Kernel will loads $MFT/$DATA's first mft record in

ntfs_read_inode_mount().

Yet the problem is that after loading, kernel doesn't check whether

attrs_offset field is a valid value.

To be more specific, if attrs_offset field is larger than bytes_allocated

field, then it may trigger the out-of-bounds read bug(reported as

use-after-free bug) in ntfs_attr_find(), when kernel tries to access the

corresponding mft record's attribute.

This patch solves it by adding the sanity check between attrs_offset field

and bytes_allocated field, after loading the first mft record.