linux-hardening - Re: [PATCH v3] checkpatch: Check for 0-length and 1-element arrays

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Message-ID: <ZHFpoIoJbvmQwE/7@work>
Date:   Fri, 26 May 2023 20:23:28 -0600
From:   "Gustavo A. R. Silva" <gustavoars@...nel.org>
To:     Kees Cook <keescook@...omium.org>
Cc:     Andy Whitcroft <apw@...onical.com>,
        Dwaipayan Ray <dwaipayanray1@...il.com>,
        Lukas Bulwahn <lukas.bulwahn@...il.com>,
        Joe Perches <joe@...ches.com>, linux-kernel@...r.kernel.org,
        linux-hardening@...r.kernel.org
Subject: Re: [PATCH v3] checkpatch: Check for 0-length and 1-element arrays

On Fri, May 26, 2023 at 07:09:33PM -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: Dwaipayan Ray <dwaipayanray1@...il.com>
> Cc: Lukas Bulwahn <lukas.bulwahn@...il.com>
> Cc: Gustavo A. R. Silva <gustavoars@...nel.org>
> Fixed-by: Joe Perches <joe@...ches.com>
> Signed-off-by: Kees Cook <keescook@...omium.org>

Acked-by: Gustavo A. R. Silva <gustavoars@...nel.org>

Thanks!
--
Gustavo

> Link: https://lore.kernel.org/r/20230517204530.never.151-kees@kernel.org
> ---
> v3:
>  - Switch to ERROR from WARN
>  - drop needless struct/union/enum prefix (joe)
>  - fix $fixed regs (joe)
> v2: https://lore.kernel.org/lkml/20230526173921.gonna.349-kees@kernel.org
> v1: https://lore.kernel.org/lkml/20230517204530.never.151-kees@kernel.org
> ---
>  scripts/checkpatch.pl | 15 +++++++++++++++
>  1 file changed, 15 insertions(+)
> 
> diff --git a/scripts/checkpatch.pl b/scripts/checkpatch.pl
> index 30b0b4fdb3bf..5307c85b93d8 100755
> --- a/scripts/checkpatch.pl
> +++ b/scripts/checkpatch.pl
> @@ -7430,6 +7430,21 @@ sub process {
>  			}
>  		}
>  
> +# check for array definition/declarations that should use flexible arrays instead
> +		if ($sline =~ /^[\+ ]\s*}\s*;\s*$/ &&
> +		    $prevline =~ /^\+\s*(?:\}|$Type)\s*$Ident\s*\[\s*(0|1)\s*\]\s*;\s*$/) {
> +			if ($1 == '0') {
> +				if (ERROR("ZERO_LENGTH_ARRAY",
> +					  "Use C99 flexible arrays instead of zero-length arrays - see https://github.com/KSPP/linux/issues/78\n" . $hereprev) &&
> +				    $fix) {
> +					$fixed[$fixlinenr - 1] =~ s/\[\s*0\s*\]/[]/;
> +				}
> +			} else {
> +				ERROR("ONE_ELEMENT_ARRAY",
> +				      "Use C99 flexible arrays instead of one-element arrays - see https://github.com/KSPP/linux/issues/79\n" . $hereprev);
> +			}
> +		}
> +
>  # nested likely/unlikely calls
>  		if ($line =~ /\b(?:(?:un)?likely)\s*\(\s*!?\s*(IS_ERR(?:_OR_NULL|_VALUE)?|WARN)/) {
>  			WARN("LIKELY_MISUSE",
> -- 
> 2.34.1
>