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Subject: Re: [PATCH 1/2] ntfs3: fix NULL deref in ntfs_update_mftmirr
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From:   Konstantin Komarov <almaz.alexandrovich@paragon-software.com>
To:     Pavel Skripkin <paskripkin@gmail.com>, <ntfs3@lists.linux.dev>
CC:     <syzbot+c95173762127ad76a824@syzkaller.appspotmail.com>,
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References: <85293dd018cae78e4d48d74ca77710b11eed59ba.1650574393.git.paskripkin@gmail.com>
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On 6/9/22 19:42, Konstantin Komarov wrote:
> 
> 
> On 6/4/22 14:42, Pavel Skripkin wrote:
>> On 4/21/22 23:53, Pavel Skripkin wrote:
>>> If ntfs_fill_super() wasn't called then sbi->sb will be equal to NULL.
>>> Code should check this ptr before dereferencing. Syzbot hit this issue
>>> via passing wrong mount param as can be seen from log below
>>>
>>> Fail log:
>>> ntfs3: Unknown parameter 'iochvrset'
>>> general protection fault, probably for non-canonical address 0xdffffc0000000003: 0000 [#1] PREEMPT SMP KASAN
>>> KASAN: null-ptr-deref in range [0x0000000000000018-0x000000000000001f]
>>> CPU: 1 PID: 3589 Comm: syz-executor210 Not tainted 5.18.0-rc3-syzkaller-00016-gb253435746d9 #0
>>> ...
>>> Call Trace:
>>>   <TASK>
>>>   put_ntfs+0x1ed/0x2a0 fs/ntfs3/super.c:463
>>>   ntfs_fs_free+0x6a/0xe0 fs/ntfs3/super.c:1363
>>>   put_fs_context+0x119/0x7a0 fs/fs_context.c:469
>>>   do_new_mount+0x2b4/0xad0 fs/namespace.c:3044
>>>   do_mount fs/namespace.c:3383 [inline]
>>>   __do_sys_mount fs/namespace.c:3591 [inline]
>>>
>>> Fixes: 82cae269cfa9 ("fs/ntfs3: Add initialization of super block")
>>> Reported-and-tested-by: syzbot+c95173762127ad76a824@syzkaller.appspotmail.com
>>> Signed-off-by: Pavel Skripkin <paskripkin@gmail.com>
>>
>> gentle ping
>>
>>
>>
>>
>> With regards,
>> Pavel Skripkin
> 
> 1st patch is correct.
> 2nd patch is a good catch, but I'm not sure if simply ignoring is good.
> If mftmirr is broken / missing, then theoretically we can continue working.
> But still it's a major fs error.
> I'm thinking about exiting mount with error, and if "force" is present,
> then continue with mount.
> I'll reply again when I'll be sure what is correct behavior.
> Thank you for your work!

I've accepted both patches.
I don't want to invent convoluted logic for mftmirr.
Thanks again for your work!