Re: [GIT PULL] Block fixes for 6.3-rc3

From: Mauro Carvalho Chehab <mchehab@kernel.org>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Miguel Ojeda <miguel.ojeda.sandonis@gmail.com>,
	Kees Cook <keescook@chromium.org>,
	Nick Desaulniers <ndesaulniers@google.com>,
	Jens Axboe <axboe@kernel.dk>,
	Nathan Chancellor <nathan@kernel.org>,
	"linux-block@vger.kernel.org" <linux-block@vger.kernel.org>,
	clang-built-linux <llvm@lists.linux.dev>,
	linux-hardening@vger.kernel.org,
	Sylwester Nawrocki <s.nawrocki@samsung.com>,
	Marek Szyprowski <m.szyprowski@samsung.com>,
	Sakari Ailus <sakari.ailus@linux.intel.com>,
	linux-media@vger.kernel.org
Subject: Re: [GIT PULL] Block fixes for 6.3-rc3
Date: Sun, 19 Mar 2023 01:48:12 +0100	[thread overview]
Message-ID: <20230319014812.2ef3c995@coco.lan> (raw)
In-Reply-To: <CAHk-=wgTSdKYbmB1JYM5vmHMcD9J9UZr0mn7BOYM_LudrP+Xvw@mail.gmail.com>

Em Fri, 17 Mar 2023 13:51:17 -0700
Linus Torvalds <torvalds@linux-foundation.org> escreveu:

> On Fri, Mar 17, 2023 at 1:42 PM Miguel Ojeda
> <miguel.ojeda.sandonis@gmail.com> wrote:
> >
> > It is comparing against just the `.code` in the `m5mols_default_ffmt`
> > table, i.e. the `MEDIA_BUS_FMT_VYUY8_2X8` (8199 = 0x2007) and
> > `MEDIA_BUS_FMT_JPEG_1X8` (16385 = 0x4001), see  
> 
> Yeah, I see what it's doing.
> 
> But:
> 
> > If the condition had `++type` instead, it would not be a problem,
> > because the loop stops before we go into the out of bounds access thus
> > no UB.  
> 
> Yeah, but clang really should have generated a proper third iteration,
> which calls that "out of bounds" case, and then returns, instead fo
> falling off the end.
> 
> I do think that on the kernel side, the fix is to just change
> 
>         } while (type++ != SIZE_DEFAULT_FFMT);
> 
> to
> 
>         } while (++type != SIZE_DEFAULT_FFMT);

Yeah, that seems to be the right fix to me too.

Ack on such change: 
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/patch/?id=efbcbb12ee99f750c9f25c873b55ad774871de2a

Regards,
Mauro

> 
> but I would *really* like clang to be fixed to not silently generate
> code that does insane things and would be basically impossible to
> debug if it ever triggers.
> 
> We would have spent a *lot* of time wondering how the heck we Oopsed
> in m5mols_get_frame_desc().
> 
>              Linus
> 

Thanks,
Mauro