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Message-ID: <201907251149.B7FD8631@keescook>
Date: Thu, 25 Jul 2019 11:50:23 -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 v6] Documentation/checkpatch: Prefer stracpy over
strcpy/strlcpy/strncpy.
On Thu, Jul 25, 2019 at 04:52:19PM +0530, NitinGote wrote:
> From: Nitin Gote <nitin.r.gote@...el.com>
>
> Added check in checkpatch.pl to deprecate strcpy(), strlcpy() and
> strncpy() in favor of stracpy().
stracpy() is preferred when the destination is a char array (rather than
a string pointer), so that likely needs to be clarified.
-Kees
>
> Updated Documentation/process/deprecated.rst for stracpy().
>
> Signed-off-by: Nitin Gote <nitin.r.gote@...el.com>
> ---
> Change log:
> v5->v6
> - Used stracpy() instead of strscpy().
>
> v4->v5
> - Change the subject line as per review comment.
> - v5 is Reviewed-by: Kees Cook <keescook@...omium.org>
>
> v3->v4
> - Removed "c:func:" from deprecated.rst as per review comment.
>
> v2->v3
> - Avoided use of $check in implementation.
> - Incorporated trivial comments.
>
> v1->v2
> - For string related apis, created different %deprecated_string_api
> and these will get emitted at CHECK Level using command line option
> -f/--file to avoid bad patched from novice script users.
>
> Documentation/process/deprecated.rst | 10 +++++-----
> scripts/checkpatch.pl | 24 ++++++++++++++++++++++++
> 2 files changed, 29 insertions(+), 5 deletions(-)
>
> diff --git a/Documentation/process/deprecated.rst b/Documentation/process/deprecated.rst
> index 49e0f64a3427..709662c71a1a 100644
> --- a/Documentation/process/deprecated.rst
> +++ b/Documentation/process/deprecated.rst
> @@ -84,7 +84,7 @@ buffer. This could result in linear overflows beyond the
> end of the buffer, leading to all kinds of misbehaviors. While
> `CONFIG_FORTIFY_SOURCE=y` and various compiler flags help reduce the
> risk of using this function, there is no good reason to add new uses of
> -this function. The safe replacement is :c:func:`strscpy`.
> +this function. The safe replacement is stracpy().
>
> strncpy() on NUL-terminated strings
> -----------------------------------
> @@ -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
> +stracpy(). If, however, the destination buffer still needs NUL-padding,
> +the safe replacement is stracpy_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
> @@ -107,7 +107,7 @@ strlcpy()
> :c:func:`strlcpy` reads the entire source buffer first, possibly exceeding
> the given limit of bytes to copy. This is inefficient and can lead to
> linear read overflows if a source string is not NUL-terminated. The
> -safe replacement is :c:func:`strscpy`.
> +safe replacement is stracpy().
>
> Variable Length Arrays (VLAs)
> -----------------------------
> diff --git a/scripts/checkpatch.pl b/scripts/checkpatch.pl
> index 342c7c781ba5..dddf5adf1aac 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" => "stracpy",
> + "strlcpy" => "stracpy",
> + "strncpy" => "stracpy - for non-NUL-terminated uses, strncpy dest should be __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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