linux-kernel - Re: [PATCH v2] bcachefs: Fix shift-out-of-bounds in bch2_stripe_to

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Message-ID: <45174791-f446-4edf-9ccd-c0021eec2895@huawei.com>
Date: Wed, 9 Oct 2024 17:25:45 +0800
From: Hongbo Li <lihongbo22@...wei.com>
To: Zhao Mengmeng <zhaomengmeng@...inos.cn>, Zhao Mengmeng
	<zhaomzhao@....com>, <kent.overstreet@...ux.dev>
CC: <linux-bcachefs@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] bcachefs: Fix shift-out-of-bounds in
 bch2_stripe_to_text



On 2024/10/9 17:16, Zhao Mengmeng wrote:
> On 2024/10/9 17:10, Hongbo Li wrote:
>>
>>
>> On 2024/10/9 13:43, Zhao Mengmeng wrote:
>>> From: Zhao Mengmeng <zhaomengmeng@...inos.cn>
>>>
>>> syzbot report a shift-out-of-bounds issue:
>>> ------------[ cut here ]------------
>>> UBSAN: shift-out-of-bounds in fs/bcachefs/ec.c:147:2
>>> shift exponent 108 is too large for 32-bit type 'unsigned int'
>>> ----
>>> Here s.csum_granularity_bits = 108, so shift is impossible for unsigned
>>> int. To fix, add a check in bch2_stripe_validate() to bail out, it has
>>> same checking logic with ec_stripe_key_init().
>>>
>>> Reported-by: syzbot+f8c98a50c323635be65d@...kaller.appspotmail.com
>>> Tested-by: syzbot+f8c98a50c323635be65d@...kaller.appspotmail.com
>>> Closes: https://syzkaller.appspot.com/bug?extid=f8c98a50c323635be65d
>>> Suggested-by: Hongbo Li <lihongbo22@...wei.com>
>>> Signed-off-by: Zhao Mengmeng <zhaomengmeng@...inos.cn>
>>> ---
>>>    fs/bcachefs/ec.c      | 6 ++++++
>>>    fs/bcachefs/errcode.h | 3 ++-
>>>    2 files changed, 8 insertions(+), 1 deletion(-)
>>>
>>> diff --git a/fs/bcachefs/ec.c b/fs/bcachefs/ec.c
>>> index 141a4c63142f..bc5ff1331c6f 100644
>>> --- a/fs/bcachefs/ec.c
>>> +++ b/fs/bcachefs/ec.c
>>> @@ -113,6 +113,12 @@ int bch2_stripe_validate(struct bch_fs *c, struct bkey_s_c k,
>>>        const struct bch_stripe *s = bkey_s_c_to_stripe(k).v;
>>>        int ret = 0;
>>>    +    if (s->csum_granularity_bits >= ilog2(le16_to_cpu(s->sectors))) {
>>
>> csum_granularity_bits should do the left shift.
> 
> If use `1 << s->csum_granularity_bits(108)` to do the check, syzbot will still trigger shift-out-of
> bounds warning. So better check the bits directly.
> 
You are right! :)

Thanks
Hongbo