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

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Date:   Sun, 19 Mar 2023 01:48:12 +0100
From:   Mauro Carvalho Chehab <mchehab@...nel.org>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     Miguel Ojeda <miguel.ojeda.sandonis@...il.com>,
        Kees Cook <keescook@...omium.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Jens Axboe <axboe@...nel.dk>,
        Nathan Chancellor <nathan@...nel.org>,
        "linux-block@...r.kernel.org" <linux-block@...r.kernel.org>,
        clang-built-linux <llvm@...ts.linux.dev>,
        linux-hardening@...r.kernel.org,
        Sylwester Nawrocki <s.nawrocki@...sung.com>,
        Marek Szyprowski <m.szyprowski@...sung.com>,
        Sakari Ailus <sakari.ailus@...ux.intel.com>,
        linux-media@...r.kernel.org
Subject: Re: [GIT PULL] Block fixes for 6.3-rc3

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

> On Fri, Mar 17, 2023 at 1:42 PM Miguel Ojeda
> <miguel.ojeda.sandonis@...il.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