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

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Message-Id: <78AAE4F3-1C2B-4EE8-AC7A-B5F3730D1DB6@toblux.com>
Date: Thu, 3 Oct 2024 17:43:02 +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 17:35, Jan Hendrik Farr <kernel@...rr.cc> wrote:
> On 03 17:30:28, Thorsten Blum wrote:
>> 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
> 
> Do you already have an open issue on the llvm github? Otherwise I'll
> open one and submit the PR shortly.

No, feel free to open one. Thanks!

>>>>> 
>>>>> 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