linux-hardening - Re: [PATCH v4] checkpatch: Check for 0-length and 1-element arrays

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Date:   Thu, 1 Jun 2023 09:06:25 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Joe Perches <joe@...ches.com>
Cc:     Andy Whitcroft <apw@...onical.com>,
        Dwaipayan Ray <dwaipayanray1@...il.com>,
        Lukas Bulwahn <lukas.bulwahn@...il.com>,
        "Gustavo A . R . Silva" <gustavoars@...nel.org>,
        linux-kernel@...r.kernel.org, linux-hardening@...r.kernel.org
Subject: Re: [PATCH v4] checkpatch: Check for 0-length and 1-element arrays

On Wed, May 31, 2023 at 10:50:58AM -0700, Joe Perches wrote:
> On Tue, 2023-05-30 at 17:49 -0700, Kees Cook wrote:
> > Fake flexible arrays have been deprecated since last millennium. Proper
> > C99 flexible arrays must be used throughout the kernel so
> > CONFIG_FORTIFY_SOURCE and CONFIG_UBSAN_BOUNDS can provide proper array
> > bounds checking.
> > 
> > Cc: Andy Whitcroft <apw@...onical.com>
> > Cc: Joe Perches <joe@...ches.com>
> > Cc: Dwaipayan Ray <dwaipayanray1@...il.com>
> > Cc: Lukas Bulwahn <lukas.bulwahn@...il.com>
> > Cc: Gustavo A. R. Silva <gustavoars@...nel.org>
> > Signed-off-by: Kees Cook <keescook@...omium.org>
> > Link: https://lore.kernel.org/r/20230517204530.never.151-kees@kernel.org
> > ---
> > v4:
> >  - combine errors (joe)
> >  - switch to kerndoc url (joe)
> >  - add __packed for struct matching (joe)
> > v3: https://lore.kernel.org/r/20230527020929.give.261-kees@kernel.org
> > v2: https://lore.kernel.org/lkml/20230526173921.gonna.349-kees@kernel.org
> > v1: https://lore.kernel.org/lkml/20230517204530.never.151-kees@kernel.org
> > ---
> >  scripts/checkpatch.pl | 10 ++++++++++
> >  1 file changed, 10 insertions(+)
> > 
> > diff --git a/scripts/checkpatch.pl b/scripts/checkpatch.pl
> > index 30b0b4fdb3bf..64d21b6aa6df 100755
> > --- a/scripts/checkpatch.pl
> > +++ b/scripts/checkpatch.pl
> > @@ -7430,6 +7430,16 @@ sub process {
> >  			}
> >  		}
> >  
> > +# check for array definition/declarations that should use flexible arrays instead
> > +		if ($sline =~ /^[\+ ]\s*}\s*;\s*$/ &&
> > +		    $prevline =~ /^\+\s*(?:\}(?:\s*__packed\s*)?|$Type)\s*$Ident\s*\[\s*(0|1)\s*\]\s*;\s*$/) {
> 
> __packed could be used when a struct is defined and so
> needs to also be added to $sline.

Agh. Yes, thank you. v5 on the way...

-- 
Kees Cook