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

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Message-ID: <Zv7HG8tR-Fdvb1SZ@archlinux>
Date: Thu, 3 Oct 2024 18:32:27 +0200
From: Jan Hendrik Farr <kernel@...rr.cc>
To: Thorsten Blum <thorsten.blum@...lux.com>
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 03 17:43:02, Thorsten Blum wrote:
> 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!

Here's the issue:
https://github.com/llvm/llvm-project/issues/111009

Here's the PR:
https://github.com/llvm/llvm-project/pull/111015

(Looks like I violated the code formatting rules somewhere, will fix)

> 
> >>>>> 
> >>>>> 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
>