From: Kees Cook <keescook@chromium.org>
To: Joe Perches <joe@perches.com>
Cc: Masahiro Yamada <masahiroy@kernel.org>,
Nick Desaulniers <ndesaulniers@google.com>,
clang-built-linux <clang-built-linux@googlegroups.com>,
stable <stable@vger.kernel.org>, Andy Lavr <andy.lavr@gmail.com>,
Arvind Sankar <nivedita@alum.mit.edu>,
Rasmus Villemoes <linux@rasmusvillemoes.dk>,
Sami Tolvanen <samitolvanen@google.com>,
Andrew Morton <akpm@linux-foundation.org>,
Andy Shevchenko <andriy.shevchenko@linux.intel.com>,
Alexandru Ardelean <alexandru.ardelean@analog.com>,
Yury Norov <yury.norov@gmail.com>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH v3] lib/string.c: implement stpcpy
Date: Thu, 27 Aug 2020 11:26:04 -0700 [thread overview]
Message-ID: <202008271124.37242A14@keescook> (raw)
In-Reply-To: <e84ea9d311fe082af8a1afe2aba48303ffbb1bf1.camel@perches.com>
On Wed, Aug 26, 2020 at 07:42:17PM -0700, Joe Perches wrote:
> On Wed, 2020-08-26 at 19:33 -0700, Kees Cook wrote:
> > 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.
>
> OK, but it is in Documentation/process/deprecated.rst
>
> strncpy() on NUL-terminated strings
"... on NUL-terminated strings". It's "valid" to use it on known-size
(either external or by definition) NUL-padded buffers (e.g. NLA_STRING).
--
Kees Cook
next prev parent reply other threads:[~2020-08-27 18:26 UTC|newest]
Thread overview: 25+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-08-25 13:58 [PATCH v3] lib/string.c: implement stpcpy Nick Desaulniers
2020-08-25 18:51 ` Nathan Chancellor
2020-08-26 15:41 ` Sedat Dilek
2020-08-26 15:58 ` Masahiro Yamada
2020-09-06 9:57 ` Kees Cook
2020-08-26 16:49 ` Masahiro Yamada
2020-08-26 16:57 ` Joe Perches
2020-08-26 16:58 ` Nick Desaulniers
2020-08-26 22:59 ` Masahiro Yamada
2020-08-26 23:38 ` Kees Cook
2020-08-26 23:57 ` Joe Perches
2020-08-27 2:33 ` Kees Cook
2020-08-27 2:42 ` Joe Perches
2020-08-27 18:26 ` Kees Cook [this message]
2020-08-27 8:59 ` Andy Shevchenko
2020-08-27 18:30 ` Kees Cook
2020-08-27 19:37 ` Joe Perches
2020-08-27 19:41 ` Kees Cook
2020-08-27 20:05 ` Andy Shevchenko
2020-08-27 22:26 ` Kees Cook
2020-08-28 8:17 ` Andy Shevchenko
2020-08-31 23:21 ` Nick Desaulniers
2020-09-01 8:51 ` David Laight
2020-08-25 14:00 Nick Desaulniers
2020-08-26 15:22 ` Kees Cook
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