From: Justin Stitt <justinstitt@google.com>
To: Geert Uytterhoeven <geert@linux-m68k.org>
Cc: Willem de Bruijn <willemdebruijn.kernel@gmail.com>,
Jason Wang <jasowang@redhat.com>,
Richard Weinberger <richard@nod.at>,
Anton Ivanov <anton.ivanov@cambridgegreys.com>,
Johannes Berg <johannes@sipsolutions.net>,
linux-um@lists.infradead.org, linux-kernel@vger.kernel.org,
linux-hardening@vger.kernel.org,
Kees Cook <keescook@chromium.org>
Subject: Re: [PATCH] um,ethertap: refactor deprecated strncpy
Date: Tue, 12 Sep 2023 13:12:35 -0700 [thread overview]
Message-ID: <CAFhGd8r9Ow2xmJ++apef0rn2DHBhKm9BvfLooMTqzyaOhqbEgQ@mail.gmail.com> (raw)
In-Reply-To: <CAMuHMdXJMZ6FebNn01C9EPsZAiJs-n5tp4j2hufAAr=zXOsSOQ@mail.gmail.com>
On Tue, Sep 12, 2023 at 12:36 AM Geert Uytterhoeven
<geert@linux-m68k.org> wrote:
>
> Hi Justin,
>
> Thanks for your patch!
>
> On Mon, Sep 11, 2023 at 7:53 PM Justin Stitt <justinstitt@google.com> wrote:
> > `strncpy` is deprecated for use on NUL-terminated destination strings [1].
> >
> > `gate_buf` should always be NUL-terminated and does not require
> > NUL-padding. It is used as a string arg inside an argv array given to
>
> Can you please explain why it does not require NUL-padding?
> It looks like this buffer is passed eventually to a user space
> application, thus possibly leaking uninitialized stack data.
It looks like it's being passed as a list of command-line arguments in
`run_helper()`. Should this be NUL-padded due to its eventual use in
user space? If we think yes I can send a v2. Thanks for pointing this
out.
>
> > `run_helper()`. Due to this, let's use `strscpy` as it guarantees
> > NUL-terminated on the destination buffer preventing potential buffer
> > overreads [2].
> >
> > This exact invocation was changed from `strcpy` to `strncpy` in commit
> > 7879b1d94badb ("um,ethertap: use strncpy") back in 2015. Let's continue
> > hardening our `str*cpy` apis and use the newer and safer `strscpy`!
> >
> > Link: www.kernel.org/doc/html/latest/process/deprecated.html#strncpy-on-nul-terminated-strings[1]
> > Link: https://manpages.debian.org/testing/linux-manual-4.8/strscpy.9.en.html [2]
> > Link: https://github.com/KSPP/linux/issues/90
> > Cc: linux-hardening@vger.kernel.org
> > Cc: Kees Cook <keescook@chromium.org>
> > Signed-off-by: Justin Stitt <justinstitt@google.com>
> > ---
> > arch/um/os-Linux/drivers/ethertap_user.c | 2 +-
> > 1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/arch/um/os-Linux/drivers/ethertap_user.c b/arch/um/os-Linux/drivers/ethertap_user.c
> > index 9483021d86dd..3363851a4ae8 100644
> > --- a/arch/um/os-Linux/drivers/ethertap_user.c
> > +++ b/arch/um/os-Linux/drivers/ethertap_user.c
> > @@ -105,7 +105,7 @@ static int etap_tramp(char *dev, char *gate, int control_me,
> > sprintf(data_fd_buf, "%d", data_remote);
> > sprintf(version_buf, "%d", UML_NET_VERSION);
> > if (gate != NULL) {
> > - strncpy(gate_buf, gate, 15);
> > + strscpy(gate_buf, gate, sizeof(gate_buf));
> > args = setup_args;
> > }
> > else args = nosetup_args;
> >
> > ---
> > base-commit: 2dde18cd1d8fac735875f2e4987f11817cc0bc2c
> > change-id: 20230911-strncpy-arch-um-os-linux-drivers-ethertap_user-c-859160d13f59
>
> Gr{oetje,eeting}s,
>
> Geert
>
> --
> Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org
>
> In personal conversations with technical people, I call myself a hacker. But
> when I'm talking to journalists I just say "programmer" or something like that.
> -- Linus Torvalds
_______________________________________________
linux-um mailing list
linux-um@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-um
prev parent reply other threads:[~2023-09-12 20:12 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-09-11 17:52 [PATCH] um,ethertap: refactor deprecated strncpy Justin Stitt
2023-09-12 7:36 ` Geert Uytterhoeven
2023-09-12 20:12 ` Justin Stitt [this message]
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=CAFhGd8r9Ow2xmJ++apef0rn2DHBhKm9BvfLooMTqzyaOhqbEgQ@mail.gmail.com \
--to=justinstitt@google.com \
--cc=anton.ivanov@cambridgegreys.com \
--cc=geert@linux-m68k.org \
--cc=jasowang@redhat.com \
--cc=johannes@sipsolutions.net \
--cc=keescook@chromium.org \
--cc=linux-hardening@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-um@lists.infradead.org \
--cc=richard@nod.at \
--cc=willemdebruijn.kernel@gmail.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for read-only IMAP folder(s) and NNTP newsgroup(s).