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

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Message-ID: <1e46f070-3e78-4a81-b7c7-ea021271b12b@huawei.com>
Date: Tue, 22 Oct 2024 10:26:18 +0800
From: Hongbo Li <lihongbo22@...wei.com>
To: Jeongjun Park <aha310510@...il.com>, <kent.overstreet@...ux.dev>,
	<mmpgouride@...il.com>
CC: <linux-bcachefs@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
	<syzbot+7f45fa9805c40db3f108@...kaller.appspotmail.com>
Subject: Re: [PATCH v3] bcachefs: fix shift oob in alloc_lru_idx_fragmentation



On 2024/10/21 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 in my humble 
opinion, the validation changes also should be added. And in addition, 
move the condition about a.data_type into data_type_movable will be 
better. Just my personal opinion.:)

[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;
> --
>