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

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Message-ID: <f8efee7cd9f6f685dcf8b90f9169029fec6481e3.camel@perches.com>
Date:   Wed, 31 May 2023 10:50:58 -0700
From:   Joe Perches <joe@...ches.com>
To:     Kees Cook <keescook@...omium.org>,
        Andy Whitcroft <apw@...onical.com>
Cc:     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 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.

		if ($sline =~ /^[\+ ]\s*}\s*(?:__packed\s*)?;\s*$/ &&

e.g.:

struct foo {
	int a;
	int b[0];
} __packed;

> +			if (ERROR("FLEXIBLE_ARRAY",
> +				  "Use C99 flexible arrays - see https://docs.kernel.org/process/deprecated.html#zero-length-and-one-element-arrays\n" . $hereprev) &&
> +			    $1 == '0' && $fix) {
> +				$fixed[$fixlinenr - 1] =~ s/\[\s*0\s*\]/[]/;
> +			}
> +		}
> +
>  # nested likely/unlikely calls
>  		if ($line =~ /\b(?:(?:un)?likely)\s*\(\s*!?\s*(IS_ERR(?:_OR_NULL|_VALUE)?|WARN)/) {
>  			WARN("LIKELY_MISUSE",