Re: [PATCH v5] Documentation/checkpatch: Prefer strscpy/strscpy_pad over strcpy/strlcpy/strncpy

[Kees Cook <keescook@chromium.org>]

On Wed, Jul 17, 2019 at 10:00:05AM +0530, NitinGote wrote:
> From: Nitin Gote <nitin.r.gote@intel.com>
> 
> Added check in checkpatch.pl to
> 1. Deprecate strcpy() in favor of strscpy().
> 2. Deprecate strlcpy() in favor of strscpy().
> 3. Deprecate strncpy() in favor of strscpy() or strscpy_pad().
> 
> Updated strncpy() section in Documentation/process/deprecated.rst
> to cover strscpy_pad() case.
> 
> Signed-off-by: Nitin Gote <nitin.r.gote@intel.com>

Reviewed-by: Kees Cook <keescook@chromium.org>

Joe, does this address your checkpatch concerns?

-Kees

> ---
>  Documentation/process/deprecated.rst |  6 +++---
>  scripts/checkpatch.pl                | 24 ++++++++++++++++++++++++
>  2 files changed, 27 insertions(+), 3 deletions(-)
> 
> diff --git a/Documentation/process/deprecated.rst b/Documentation/process/deprecated.rst
> index 49e0f64a3427..c348ef9d44f5 100644
> --- a/Documentation/process/deprecated.rst
> +++ b/Documentation/process/deprecated.rst
> @@ -93,9 +93,9 @@ will be NUL terminated. This can lead to various linear read overflows
>  and other misbehavior due to the missing termination. It also NUL-pads the
>  destination buffer if the source contents are shorter than the destination
>  buffer size, which may be a needless performance penalty for callers using
> -only NUL-terminated strings. The safe replacement is :c:func:`strscpy`.
> -(Users of :c:func:`strscpy` still needing NUL-padding will need an
> -explicit :c:func:`memset` added.)
> +only NUL-terminated strings. In this case, the safe replacement is
> +strscpy(). If, however, the destination buffer still needs NUL-padding,
> +the safe replacement is strscpy_pad().
> 
>  If a caller is using non-NUL-terminated strings, :c:func:`strncpy()` can
>  still be used, but destinations should be marked with the `__nonstring
> diff --git a/scripts/checkpatch.pl b/scripts/checkpatch.pl
> index bb28b178d929..1bb12127115d 100755
> --- a/scripts/checkpatch.pl
> +++ b/scripts/checkpatch.pl
> @@ -605,6 +605,20 @@ foreach my $entry (keys %deprecated_apis) {
>  }
>  $deprecated_apis_search = "(?:${deprecated_apis_search})";
> 
> +our %deprecated_string_apis = (
> +        "strcpy"				=> "strscpy",
> +        "strlcpy"				=> "strscpy",
> +        "strncpy"				=> "strscpy, strscpy_pad or for non-NUL-terminated strings, strncpy() can still be used, but destinations should be marked with __nonstring",
> +);
> +
> +#Create a search pattern for all these strings apis to speed up a loop below
> +our $deprecated_string_apis_search = "";
> +foreach my $entry (keys %deprecated_string_apis) {
> +        $deprecated_string_apis_search .= '|' if ($deprecated_string_apis_search ne "");
> +        $deprecated_string_apis_search .= $entry;
> +}
> +$deprecated_string_apis_search = "(?:${deprecated_string_apis_search})";
> +
>  our $mode_perms_world_writable = qr{
>  	S_IWUGO		|
>  	S_IWOTH		|
> @@ -6446,6 +6460,16 @@ sub process {
>  			     "Deprecated use of '$deprecated_api', prefer '$new_api' instead\n" . $herecurr);
>  		}
> 
> +# check for string deprecated apis
> +		if ($line =~ /\b($deprecated_string_apis_search)\b\s*\(/) {
> +			my $deprecated_string_api = $1;
> +			my $new_api = $deprecated_string_apis{$deprecated_string_api};
> +			my $msg_level = \&WARN;
> +			$msg_level = \&CHK if ($file);
> +			&{$msg_level}("DEPRECATED_API",
> +				      "Deprecated use of '$deprecated_string_api', prefer '$new_api' instead\n" . $herecurr);
> +		}
> +
>  # check for various structs that are normally const (ops, kgdb, device_tree)
>  # and avoid what seem like struct definitions 'struct foo {'
>  		if ($line !~ /\bconst\b/ &&
> --
> 2.17.1
> 

-- 
Kees Cook