A null-ptr-deref bug be triggered when write to an ICB inode

[butt3rflyh4ck <butterflyhuangxx@gmail.com>]

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Hi, there is a null pointer dereference bug that would be triggered
when writing something to an ICB inode, I reproduce in the latest
kernel.

First mount a malicious udf image, secondly create a dir named
"./file0", then create a file named "file1" in the file0 directory.
Then write something to "./file0/file1", then invoke
udf_file_write_iter function.

the udf_file_write_iter code:
```
static ssize_t udf_file_write_iter(struct kiocb *iocb, struct iov_iter *from)
{
ssize_t retval;
struct file *file = iocb->ki_filp;
struct inode *inode = file_inode(file);
struct udf_inode_info *iinfo = UDF_I(inode);
int err;

inode_lock(inode);

retval = generic_write_checks(iocb, from);
if (retval <= 0)
goto out;

down_write(&iinfo->i_data_sem);
if (iinfo->i_alloc_type == ICBTAG_FLAG_AD_IN_ICB) {   ///[1 ]
loff_t end = iocb->ki_pos + iov_iter_count(from);   ///[2] end =
iocb->ki_pos + i->count = iocb->ki_pos + user_write_size

if (inode->i_sb->s_blocksize <
(udf_file_entry_alloc_offset(inode) + end)) {  /// [3]
err = udf_expand_file_adinicb(inode);

....

}
```
[1] if the inode is ICBTAG_FLAG_AD_IN_ICB type, [2] then get a end,
[3] compare blocksize and end, if blocksize is smaller then invoke
udf_expand_file_adinicb to modify inode.
Next, in the process of expanding the block, trigger the bug.

the crash log:
```
[   82.827914][ T6441] loop0: detected capacity change from 0 to 5656
[   82.830192][ T6441] UDF-fs: warning (device loop0): udf_load_vrs:
No anchor found
[   82.831014][ T6441] UDF-fs: Scanning with blocksize 512 failed
[   82.833515][ T6441] UDF-fs: INFO Mounting volume 'LinuxUDF',
timestamp 2020/09/19 18:44 (1000)
[   82.835323][ T6441] general protection fault, probably for
non-canonical address 0xdffffc0000000015: 0000 [#1] PREEMPT SMP KASAN
[   82.836556][ T6441] KASAN: null-ptr-deref in range
[0x00000000000000a8-0x00000000000000af]
[   82.837437][ T6441] CPU: 0 PID: 6441 Comm: percpu_counter_ Not
tainted 5.16.0+ #34
[   82.838242][ T6441] Hardware name: QEMU Standard PC (i440FX + PIIX,
1996), BIOS 1.13.0-1ubuntu1 04/01/2014
[   82.838885][   T26] audit: type=1800 audit(1642070781.843:2):
pid=6441 uid=0 auid=0 ses=1 subj==unconfined op=collect_data
cause=failed(directio) comm="percpu_count0
[   82.843723][ T6441] RIP: 0010:percpu_counter_add_batch+0x3e/0x130
[   82.843757][ T6441] Code: 53 48 63 da e8 73 44 b4 fd 4c 8d 7d 20 48
c7 c7 40 0d dd 88 e8 c3 63 94 04 4c 89 fa 48 b8 00 00 00 00 00 fc ff
df 48 c1 ea 03 <80> 3c 02 0d
[   82.843760][ T6441] RSP: 0018:ffffc9000634f9e8 EFLAGS: 00010012
[   82.843765][ T6441] RAX: dffffc0000000000 RBX: 0000000000000010
RCX: 1ffffffff1a443f8
[   82.843768][ T6441] RDX: 0000000000000015 RSI: ffffffff88dd0d40
RDI: ffffffff88dac160
[   82.843769][ T6441] RBP: 0000000000000088 R08: 0000000000000004
R09: fffff940000bb9b9
[   82.843771][ T6441] R10: ffffea00005dcdc7 R11: fffff940000bb9b8
R12: 0000000000000000
[   82.843772][ T6441] R13: 0000000000000001 R14: 0000000000000001
R15: 00000000000000a8
[   82.843776][ T6441] FS:  00000000014e5880(0000)
GS:ffff88802d400000(0000) knlGS:0000000000000000
[   82.843780][ T6441] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[   82.843785][ T6441] CR2: 0000000020000000 CR3: 00000000185a2000
CR4: 00000000000006f0
[   82.843791][ T6441] Call Trace:
[   82.843795][ T6441]  <TASK>
[   82.843799][ T6441]  __folio_start_writeback+0x64f/0x7b0
[   82.843805][ T6441]  ? domain_dirty_limits+0x350/0x350
[   82.843808][ T6441]  ? udf_get_block+0x208/0x4d0
[   82.843813][ T6441]  ? errseq_set+0x7b/0xe0
[   82.843817][ T6441]  __block_write_full_page+0x9b0/0xdc0
[   82.843822][ T6441]  ? udf_block_map+0x250/0x250
[   82.843824][ T6441]  ? end_buffer_write_sync+0xb0/0xb0
[   82.843827][ T6441]  udf_expand_file_adinicb+0x3bc/0xcc0
[   82.843830][ T6441]  ? udf_update_inode+0x3370/0x3370
[   82.843833][ T6441]  udf_file_write_iter+0x298/0x440
[   82.843835][ T6441]  ? _raw_spin_lock+0x88/0x110
[   82.843844][ T6441]  new_sync_write+0x37f/0x620
[   82.843848][ T6441]  ? new_sync_read+0x610/0x610
[   82.843850][ T6441]  ? common_file_perm+0x196/0x5f0
[   82.843855][ T6441]  ? apparmor_path_rmdir+0x20/0x20
[   82.843857][ T6441]  ? kmem_cache_free+0x9a/0x490
[   82.843860][ T6441]  ? security_file_permission+0x49/0x570
[   82.843864][ T6441]  vfs_write+0x41d/0x7b0
[   82.892153][ T6441]  ksys_write+0xe8/0x1c0
[   82.894156][ T6441]  ? __ia32_sys_read+0xa0/0xa0
[   82.895079][ T6441]  do_syscall_64+0x35/0xb0
[   82.895830][ T6441]  entry_SYSCALL_64_after_hwframe+0x44/0xae
[   82.896810][ T6441] RIP: 0033:0x44eafd
[   82.897449][ T6441] Code: 02 b8 ff ff ff ff c3 66 0f 1f 44 00 00 f3
0f 1e fa 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 f8
[   82.900627][ T6441] RSP: 002b:00007ffec490a868 EFLAGS: 00000246
ORIG_RAX: 0000000000000001
[   82.901996][ T6441] RAX: ffffffffffffffda RBX: 0000000000400530
RCX: 000000000044eafd
[   82.903311][ T6441] RDX: 000000000000fdef RSI: 0000000020000080
RDI: 0000000000000004
[   82.904625][ T6441] RBP: 00007ffec490a880 R08: 0000000000000000
R09: 0000000000000000
[   82.905919][ T6441] R10: 0000000000000000 R11: 0000000000000246
R12: 0000000000403b00
[   82.907212][ T6441] R13: 0000000000000000 R14: 00000000004c6018
R15: 0000000000000000
[   82.908522][ T6441]  </TASK>
[   82.909026][ T6441] Modules linked in:
[   82.909671][ T6441] ---[ end trace 99ae3d17814cae89 ]---
[   82.910556][ T6441] RIP: 0010:percpu_counter_add_batch+0x3e/0x130
[   82.911627][ T6441] Code: 53 48 63 da e8 73 44 b4 fd 4c 8d 7d 20 48
c7 c7 40 0d dd 88 e8 c3 63 94 04 4c 89 fa 48 b8 00 00 00 00 00 fc ff
df 48 c1 ea 03 <80> 3c 02 0d
[   82.914533][ T6441] RSP: 0018:ffffc9000634f9e8 EFLAGS: 00010012
[   82.915482][ T6441] RAX: dffffc0000000000 RBX: 0000000000000010
RCX: 1ffffffff1a443f8
[   82.916677][ T6441] RDX: 0000000000000015 RSI: ffffffff88dd0d40
RDI: ffffffff88dac160
[   82.917868][ T6441] RBP: 0000000000000088 R08: 0000000000000004
R09: fffff940000bb9b9
[   82.919086][ T6441] R10: ffffea00005dcdc7 R11: fffff940000bb9b8
R12: 0000000000000000
[   82.920262][ T6441] R13: 0000000000000001 R14: 0000000000000001
R15: 00000000000000a8
[   82.921457][ T6441] FS:  00000000014e5880(0000)
GS:ffff88802d400000(0000) knlGS:0000000000000000
[   82.922825][ T6441] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[   82.923845][ T6441] CR2: 0000000020000000 CR3: 00000000185a2000
CR4: 00000000000006f0
[   82.925080][ T6441] Kernel panic - not syncing: Fatal exception
[   82.926163][ T6441] Kernel Offset: disabled
[   82.926853][ T6441] Rebooting in 86400 seconds..

```
The attachment is a reproduce.


Regards,
 butt3rflyh4ck.


--
Active Defense Lab of Venustech

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