linux-kernel - Re: [PATCH v3] bcachefs: fix shift oob in alloc_lru_idx

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Message-ID: <10aed636-b665-49f0-8fa3-fcb5504c13c6@huawei.com>
Date: Tue, 22 Oct 2024 11:05:55 +0800
From: Hongbo Li <lihongbo22@...wei.com>
To: Alan Huang <mmpgouride@...il.com>
CC: Jeongjun Park <aha310510@...il.com>, Kent Overstreet
	<kent.overstreet@...ux.dev>, <linux-bcachefs@...r.kernel.org>, LKML
	<linux-kernel@...r.kernel.org>,
	<syzbot+7f45fa9805c40db3f108@...kaller.appspotmail.com>
Subject: Re: [PATCH v3] bcachefs: fix shift oob in alloc_lru_idx_fragmentation



On 2024/10/22 10:38, Alan Huang wrote:
> On Oct 22, 2024, at 10:26, Hongbo Li <lihongbo22@...wei.com> wrote:
>>
>>
>>
>> On 2024/10/21 23:43, Jeongjun Park wrote:
>>> The size of a.data_type is set abnormally large, causing shift-out-of-bounds.
>>> To fix this, we need to add validation on a.data_type in
>>> alloc_lru_idx_fragmentation().
>>> Reported-by: syzbot+7f45fa9805c40db3f108@...kaller.appspotmail.com
>>> Fixes: 260af1562ec1 ("bcachefs: Kill alloc_v4.fragmentation_lru")
>>> Signed-off-by: Jeongjun Park <aha310510@...il.com>
>>> ---
>>>   fs/bcachefs/alloc_background.h | 3 +++
>>>   1 file changed, 3 insertions(+)
>>> diff --git a/fs/bcachefs/alloc_background.h b/fs/bcachefs/alloc_background.h
>>> index f8e87c6721b1..163a67b97a40 100644
>>> --- a/fs/bcachefs/alloc_background.h
>>> +++ b/fs/bcachefs/alloc_background.h
>>> @@ -168,6 +168,9 @@ static inline bool data_type_movable(enum bch_data_type type)
>>>   static inline u64 alloc_lru_idx_fragmentation(struct bch_alloc_v4 a,
>>>          struct bch_dev *ca)
>>>   {
>>> + if (a.data_type >= BCH_DATA_NR)
>>> + return 0;
>>> +
>>
>> oh, I found I have done the same thing in [1]("Re: [syzbot] [bcachefs?] UBSAN: shift-out-of-bounds in bch2_alloc_to_text"). But
> 
> Your patch there is still triggering the issue.
Yeah, it just notify the issue and not prevent the issue. So I found it 
should add a.data_type condition indeed. :)
> 
>> in my humble opinion, the validation changes also should be added. And in addition, move the condition about a.data_type into
> 
> There is already the validation:
> 
> bkey_fsck_err_on(alloc_data_type(a, a.data_type) != a.data_type

This is actually not enough. This only do some transition check. For 
example, if a.data_type break when bch2_bucket_sectors_dirty (the data 
corruption can lead to various situations occurring) is true, the helper 
does noting.

Thanks,
Hongbo

> 
> And the unknown data type is already printed in bch2_prt_data_type, additional validation doesn’t help much.
> 
>> data_type_movable will be better. Just my personal opinion.:)
> 
> In my personal opinion, I don’t think so :)
> 
>>
>> [1] https://www.spinics.net/lists/kernel/msg5412619.html
>>
>> Thanks,
>> Hongbo
>>
>>>    if (!data_type_movable(a.data_type) ||
>>>        !bch2_bucket_sectors_fragmented(ca, a))
>>>    return 0;
>>> --
> 
>