linux-kernel - Re: [PATCH] btrfs: add a sanity check for btrfs root

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Message-ID: <e5bc8c4e-771f-4cc7-91e7-291018b9468c@gmx.com>
Date: Sat, 26 Oct 2024 07:33:59 +1030
From: Qu Wenruo <quwenruo.btrfs@....com>
To: dsterba@...e.cz
Cc: Lizhi Xu <lizhi.xu@...driver.com>,
 syzbot+3030e17bd57a73d39bd7@...kaller.appspotmail.com, clm@...com,
 dsterba@...e.com, josef@...icpanda.com, linux-btrfs@...r.kernel.org,
 linux-kernel@...r.kernel.org, syzkaller-bugs@...glegroups.com
Subject: Re: [PATCH] btrfs: add a sanity check for btrfs root



在 2024/10/26 04:33, David Sterba 写道:
> On Fri, Oct 25, 2024 at 08:23:07PM +1030, Qu Wenruo wrote:
>>
>>
>> 在 2024/10/25 15:25, Lizhi Xu 写道:
>>> Syzbot report a null-ptr-deref in btrfs_search_slot.
>>> It use the input logical can't find the extent root in extent_from_logical,
>>> and triger the null-ptr-deref in btrfs_search_slot.
>>> Add sanity check for btrfs root before using it in btrfs_search_slot.
>>
>> Although I'd prefer to explain a little more about why the NULL root
>> pointer can happen (caused by the rescue=all mount option), which can
>> cause NULL root pointer for non-critical tree roots, like
>> uuid/csum/extent or even device trees.
>>
>> You don't need to bother sending an update.
>> I can add such info when pushing to the maintainer's tree.
>>
>>>
>>> Reported-by: syzbot+3030e17bd57a73d39bd7@...kaller.appspotmail.com
>>> Closes: https://syzkaller.appspot.com/bug?extid=3030e17bd57a73d39bd7
>>> Signed-off-by: Lizhi Xu <lizhi.xu@...driver.com>
>>
>> Reviewed-by: Qu Wenruo <wqu@...e.com>
>
>>> @@ -2023,6 +2023,10 @@ int btrfs_search_slot(struct btrfs_trans_handle *trans, struct btrfs_root *root,
>>>    	int min_write_lock_level;
>>>    	int prev_cmp;
>>>
>>> +	if (!root)
>>> +		return -EINVAL;
>
> The function returns errors indirectly so it's not clear which could be
> ultimately returned. I did a quick search over the calls starting in
> btrfs_search_slot() and it seems that EINVAL is not used so we'd know if
> it ends up in some error report. The ones I found: EAGAIN, EIO, EUCLEAN,
> ENOMEM.
>

If you want, I can add extra (ratelimited though) error/warning message
for such cases.

Considering this is only possible for rescue=all cases, extra error
messages should be fine.

Or do you prefer some more rare return values?

Thanks,
Qu