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Date: Mon, 22 Jul 2019 10:30:29 -0700
From: Kees Cook <keescook@...omium.org>
To: NitinGote <nitin.r.gote@...el.com>
Cc: joe@...ches.com, corbet@....net, akpm@...ux-foundation.org,
apw@...onical.com, linux-doc@...r.kernel.org,
kernel-hardening@...ts.openwall.com
Subject: Re: [PATCH v5] Documentation/checkpatch: Prefer strscpy/strscpy_pad
over strcpy/strlcpy/strncpy
On Wed, Jul 17, 2019 at 10:00:05AM +0530, NitinGote wrote:
> From: Nitin Gote <nitin.r.gote@...el.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@...el.com>
Reviewed-by: Kees Cook <keescook@...omium.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
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