linux-hardening - Re: [REGRESSION][BISECTED] erroneous buffer overflow detected in bch2_xattr

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Message-Id: <83834AC8-0109-40C5-A80C-8BFFA8F16B19@toblux.com>
Date: Thu, 3 Oct 2024 17:30:28 +0200
From: Thorsten Blum <thorsten.blum@...lux.com>
To: Jan Hendrik Farr <kernel@...rr.cc>
Cc: Kees Cook <kees@...nel.org>,
 kent.overstreet@...ux.dev,
 regressions@...ts.linux.dev,
 linux-bcachefs@...r.kernel.org,
 linux-hardening@...r.kernel.org,
 linux-kernel@...r.kernel.org,
 ardb@...nel.org,
 morbo@...gle.com
Subject: Re: [REGRESSION][BISECTED] erroneous buffer overflow detected in
 bch2_xattr_validate

On 3. Oct 2024, at 17:22, Jan Hendrik Farr <kernel@...rr.cc> wrote:
> On 03 17:02:07, Thorsten Blum wrote:
>> On 3. Oct 2024, at 15:12, Jan Hendrik Farr <kernel@...rr.cc> wrote:
>>> On 03 15:07:52, Thorsten Blum wrote:
>>>> On 3. Oct 2024, at 13:33, Jan Hendrik Farr <kernel@...rr.cc> wrote:
>>>>>> [...]
>>>>> 
>>>>> This issue is now fixed on the llvm main branch:
>>>>> https://github.com/llvm/llvm-project/commit/882457a2eedbe6d53161b2f78fcf769fc9a93e8a
>>>> 
>>>> Thanks!
>>>> 
>>>> Do you know if it also fixes the different sizes here:
>>>> https://godbolt.org/z/vvK9PE1Yq
>>> 
>>> Unfortunately this still prints 36.
>> 
>> I just realized that the counted_by attribute itself causes the 4 bytes
>> difference. When you remove the attribute, the sizes are equal again.
> 
> But we want these attributes to be in the kernel, so that
> bounds-checking can be done in more scenarios, right?

Yes

> This changes clang to print 40, right? gcc prints 40 in the example
> whether the attribute is there or not.

Yes, clang prints 36 with and 40 without the attribute; gcc always 40.

>>>> I ran out of disk space when compiling llvm :0
>>>> 
>>>>> So presumably this will go into 19.1.2, not sure what this means for
>>>>> distros that ship clang 18. Will they have to be notified to backport
>>>>> this?
>>>>> 
>>>>> Best Regards
>>>>> Jan