Re: [PATCH v3] lib/string.c: implement stpcpy

[Kees Cook <keescook@chromium.org>]

On Wed, Aug 26, 2020 at 04:57:41PM -0700, Joe Perches wrote:
> On Wed, 2020-08-26 at 16:38 -0700, Kees Cook wrote:
> > On Thu, Aug 27, 2020 at 07:59:45AM +0900, Masahiro Yamada wrote:
> []
> > > OK, then stpcpy(), strcpy() and sprintf()
> > > have the same level of unsafety.
> > 
> > Yes. And even snprintf() is dangerous because its return value is how
> > much it WOULD have written, which when (commonly) used as an offset for
> > further pointer writes, causes OOB writes too. :(
> > https://github.com/KSPP/linux/issues/105
> > 
> > > strcpy() is used everywhere.
> > 
> > Yes. It's very frustrating, but it's not an excuse to continue
> > using it nor introducing more bad APIs.
> > 
> > $ git grep '\bstrcpy\b' | wc -l
> > 2212
> > $ git grep '\bstrncpy\b' | wc -l
> > 751
> > $ git grep '\bstrlcpy\b' | wc -l
> > 1712
> > 
> > $ git grep '\bstrscpy\b' | wc -l
> > 1066
> > 
> > https://www.kernel.org/doc/html/latest/process/deprecated.html#strcpy
> > https://github.com/KSPP/linux/issues/88
> > 
> > https://www.kernel.org/doc/html/latest/process/deprecated.html#strncpy-on-nul-terminated-strings
> > https://github.com/KSPP/linux/issues/89
> > 
> > https://www.kernel.org/doc/html/latest/process/deprecated.html#strlcpy
> > https://github.com/KSPP/linux/issues/90
> > 
> > We have no way right now to block the addition of deprecated API usage,
> > which makes ever catching up on this replacement very challenging.
> 
> These could be added to checkpatch's deprecated_api test.
> ---
>  scripts/checkpatch.pl | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/scripts/checkpatch.pl b/scripts/checkpatch.pl
> index 149518d2a6a7..f9ccb2a63a95 100755
> --- a/scripts/checkpatch.pl
> +++ b/scripts/checkpatch.pl
> @@ -605,6 +605,9 @@ foreach my $entry (@mode_permission_funcs) {
>  $mode_perms_search = "(?:${mode_perms_search})";
>  
>  our %deprecated_apis = (
> +	"strcpy"				=> "strscpy",
> +	"strncpy"				=> "strscpy",
> +	"strlcpy"				=> "strscpy",
>  	"synchronize_rcu_bh"			=> "synchronize_rcu",
>  	"synchronize_rcu_bh_expedited"		=> "synchronize_rcu_expedited",
>  	"call_rcu_bh"				=> "call_rcu",
> 
> 

Good idea, yeah. We, unfortunately, need to leave strncpy() off this
list for now because it's not *strictly* deprecated (see the notes in
bug report[1]), but the others can be.

[1] https://github.com/KSPP/linux/issues/89

-- 
Kees Cook