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

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Message-ID: <ZxBdSKuDWh6w_w-z@archlinux>
Date: Thu, 17 Oct 2024 02:41:44 +0200
From: Jan Hendrik Farr <kernel@...rr.cc>
To: Bill Wendling <morbo@...gle.com>
Cc: Kees Cook <kees@...nel.org>, Thorsten Blum <thorsten.blum@...lux.com>,
	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
Subject: Re: [REGRESSION][BISECTED] erroneous buffer overflow detected in
 bch2_xattr_validate

> I would be in favor of disabling __bdos on a whole struct pointer if
> it will match the functionality between the compilers. I don't think
> Qing has that on her plate at the moment, but when / if she revisits
> that we can discuss exactly how to perform the calculations then.

That's a good approach from my perspective.

To get this done we would:

Now:
1. Disable the __counted_by attribute calculation in clang for whole
struct __bdos cases like in [1] and get this into the next clang point
release (19.1.3)

2. In the kernel, disable __counted_by for clang versions < 19.1.3. Also
backport that into the stable kernels

In the future:
3. Try and figure out what the correct counted_by calculation for whole
structs should be in conjunction with gcc and clang. Either provide an
option in clang and gcc to follow the kernels expectations or change
struct_size in the kernel to match gcc's and clang's future behavior.

[1] https://github.com/llvm/llvm-project/pull/112636

Best Regards
Jan