From: Kees Cook <keescook@chromium.org> To: Alan Cox <gnomes@lxorguk.ukuu.org.uk> Cc: Matt Brown <matt@nmatt.com>, Casey Schaufler <casey@schaufler-ca.com>, Boris Lukashev <blukashev@sempervictus.com>, Greg KH <gregkh@linuxfoundation.org>, "Serge E. Hallyn" <serge@hallyn.com>, "kernel-hardening@lists.openwall.com" <kernel-hardening@lists.openwall.com>, linux-security-module <linux-security-module@vger.kernel.org>, linux-kernel <linux-kernel@vger.kernel.org> Subject: Re: [kernel-hardening] Re: [PATCH v7 2/2] security: tty: make TIOCSTI ioctl require CAP_SYS_ADMIN Date: Thu, 1 Jun 2017 11:58:42 -0700 [thread overview] Message-ID: <CAGXu5jLefv=T3mCYryqh2pYjYonFsTQZSLsHqLK75CKvSmgb-w@mail.gmail.com> (raw) In-Reply-To: <20170601140812.583cf0a5@alans-desktop> On Thu, Jun 1, 2017 at 6:08 AM, Alan Cox <gnomes@lxorguk.ukuu.org.uk> wrote: >> I still cannot wrap my head around why providing users with a >> protection is a bad thing. Yes, the other tty games are bad, but this >> fixes a specific and especially bad case that is easy to kill. It's >> got a Kconfig and a sysctl. It's not on by default. This protects the >> common case of privileged ttys that aren't attached to consoles, etc, > > Which just leads to stuff not getting fixed. Like all the code out there > today which is still vulnerable to selection based attacks because people > didn't do the job right when "fixing" stuff because they are not > thinking about security at a systems level but just tickboxing CVEs. There's a difference between "bugs" and "security bugs". Letting security bugs continue to get exploited because we want to flush out bugs seems insensitive to the people getting attacked. I'd rather protect against a class of bug than have to endless fix each bug. > I'm not against doing something to protect the container folks, but that > something as with Android is a whitelist of ioctls. And if we need to do > this with a kernel hook lets do it properly. > > Remember the namespace of the tty on creation > If the magic security flag is set then > Apply a whitelist to *any* tty ioctl call where the ns doesn't > match > > and we might as well just take the Android whitelist since they've kindly > built it for us all! > > In the tty layer it ends up being something around 10 lines of code and > some other file somewhere in security/ that's just a switch or similar > with the whitelisted ioctl codes in it. > > That (or a similar SELinux ruleset) would actually fix the problem. > SELinux would be better because it can also apply the rules when doing > things like su/sudo/... Just to play devil's advocate, wouldn't such a system continue to not address your physical-console concerns? I wouldn't want to limit the protection to only containers (but it's a good start), since it wouldn't protect people not using containers that still have a privileged TTY attached badly somewhere. If you're talking about wholistic SELinux policy, sure, I could imagine a wholistic fix. But for the tons of people without a comprehensive SELinux policy, the proposed protection continues to make sense. -Kees -- Kees Cook Pixel Security
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From: keescook@chromium.org (Kees Cook) To: linux-security-module@vger.kernel.org Subject: [kernel-hardening] Re: [PATCH v7 2/2] security: tty: make TIOCSTI ioctl require CAP_SYS_ADMIN Date: Thu, 1 Jun 2017 11:58:42 -0700 [thread overview] Message-ID: <CAGXu5jLefv=T3mCYryqh2pYjYonFsTQZSLsHqLK75CKvSmgb-w@mail.gmail.com> (raw) In-Reply-To: <20170601140812.583cf0a5@alans-desktop> On Thu, Jun 1, 2017 at 6:08 AM, Alan Cox <gnomes@lxorguk.ukuu.org.uk> wrote: >> I still cannot wrap my head around why providing users with a >> protection is a bad thing. Yes, the other tty games are bad, but this >> fixes a specific and especially bad case that is easy to kill. It's >> got a Kconfig and a sysctl. It's not on by default. This protects the >> common case of privileged ttys that aren't attached to consoles, etc, > > Which just leads to stuff not getting fixed. Like all the code out there > today which is still vulnerable to selection based attacks because people > didn't do the job right when "fixing" stuff because they are not > thinking about security at a systems level but just tickboxing CVEs. There's a difference between "bugs" and "security bugs". Letting security bugs continue to get exploited because we want to flush out bugs seems insensitive to the people getting attacked. I'd rather protect against a class of bug than have to endless fix each bug. > I'm not against doing something to protect the container folks, but that > something as with Android is a whitelist of ioctls. And if we need to do > this with a kernel hook lets do it properly. > > Remember the namespace of the tty on creation > If the magic security flag is set then > Apply a whitelist to *any* tty ioctl call where the ns doesn't > match > > and we might as well just take the Android whitelist since they've kindly > built it for us all! > > In the tty layer it ends up being something around 10 lines of code and > some other file somewhere in security/ that's just a switch or similar > with the whitelisted ioctl codes in it. > > That (or a similar SELinux ruleset) would actually fix the problem. > SELinux would be better because it can also apply the rules when doing > things like su/sudo/... Just to play devil's advocate, wouldn't such a system continue to not address your physical-console concerns? I wouldn't want to limit the protection to only containers (but it's a good start), since it wouldn't protect people not using containers that still have a privileged TTY attached badly somewhere. If you're talking about wholistic SELinux policy, sure, I could imagine a wholistic fix. But for the tons of people without a comprehensive SELinux policy, the proposed protection continues to make sense. -Kees -- Kees Cook Pixel Security -- To unsubscribe from this list: send the line "unsubscribe linux-security-module" in the body of a message to majordomo at vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
next prev parent reply other threads:[~2017-06-01 18:58 UTC|newest] Thread overview: 132+ messages / expand[flat|nested] mbox.gz Atom feed top 2017-05-29 21:37 [PATCH v7 0/2] security: tty: make TIOCSTI ioctl require CAP_SYS_ADMIN Matt Brown 2017-05-29 21:37 ` [kernel-hardening] " Matt Brown 2017-05-29 21:37 ` Matt Brown 2017-05-29 21:37 ` [PATCH v7 1/2] security: tty: Add owner user namespace to tty_struct Matt Brown 2017-05-29 21:37 ` [kernel-hardening] " Matt Brown 2017-05-29 21:37 ` Matt Brown 2017-05-29 21:38 ` [PATCH v7 2/2] security: tty: make TIOCSTI ioctl require CAP_SYS_ADMIN Matt Brown 2017-05-29 21:38 ` [kernel-hardening] " Matt Brown 2017-05-29 21:38 ` Matt Brown 2017-05-29 22:26 ` Alan Cox 2017-05-29 22:26 ` [kernel-hardening] " Alan Cox 2017-05-29 22:26 ` Alan Cox 2017-05-29 23:51 ` [kernel-hardening] " Boris Lukashev 2017-05-29 23:51 ` Boris Lukashev 2017-05-30 0:27 ` Casey Schaufler 2017-05-30 0:27 ` Casey Schaufler 2017-05-30 2:00 ` Matt Brown 2017-05-30 2:00 ` Matt Brown 2017-05-30 2:46 ` Casey Schaufler 2017-05-30 2:46 ` Casey Schaufler 2017-05-30 3:18 ` Matt Brown 2017-05-30 3:18 ` Matt Brown 2017-05-30 12:24 ` Alan Cox 2017-05-30 12:24 ` Alan Cox 2017-05-30 16:28 ` Matt Brown 2017-05-30 16:28 ` Matt Brown 2017-05-30 16:44 ` Daniel Micay 2017-05-30 16:44 ` Daniel Micay 2017-05-30 18:32 ` Stephen Smalley 2017-05-30 18:32 ` Stephen Smalley 2017-05-30 18:44 ` Nick Kralevich 2017-05-30 18:44 ` Nick Kralevich 2017-05-30 18:57 ` Matt Brown 2017-05-30 18:57 ` Matt Brown 2017-05-30 20:22 ` Daniel Micay 2017-05-30 20:22 ` Daniel Micay 2017-05-30 23:00 ` Matt Brown 2017-05-30 23:00 ` Matt Brown 2017-05-30 23:40 ` Daniel Micay 2017-05-30 23:40 ` Daniel Micay 2017-05-30 23:59 ` Matt Brown 2017-05-30 23:59 ` Matt Brown 2017-05-30 22:51 ` Alan Cox 2017-05-30 22:51 ` Alan Cox 2017-05-30 23:19 ` Matt Brown 2017-05-30 23:19 ` Matt Brown 2017-05-30 23:56 ` Alan Cox 2017-05-30 23:56 ` Alan Cox 2017-06-01 2:35 ` Kees Cook 2017-06-01 2:35 ` Kees Cook 2017-06-01 2:35 ` Kees Cook 2017-06-01 7:12 ` lazytyped 2017-06-01 18:46 ` Kees Cook 2017-06-01 22:56 ` James Morris 2017-06-02 18:46 ` Kees Cook 2017-06-01 13:08 ` Alan Cox 2017-06-01 13:08 ` Alan Cox 2017-06-01 13:08 ` Alan Cox 2017-06-01 17:18 ` Serge E. Hallyn 2017-06-01 17:18 ` Serge E. Hallyn 2017-06-01 17:18 ` Serge E. Hallyn 2017-06-01 21:26 ` Alan Cox 2017-06-01 21:26 ` Alan Cox 2017-06-01 21:26 ` Alan Cox 2017-06-01 18:58 ` Kees Cook [this message] 2017-06-01 18:58 ` Kees Cook 2017-06-01 18:58 ` Kees Cook 2017-06-01 21:24 ` Alan Cox 2017-06-01 21:24 ` Alan Cox 2017-06-01 21:24 ` Alan Cox 2017-06-02 14:46 ` Matt Brown 2017-06-02 14:46 ` Matt Brown 2017-06-02 14:46 ` Matt Brown 2017-06-02 15:36 ` Serge E. Hallyn 2017-06-02 15:36 ` Serge E. Hallyn 2017-06-02 15:36 ` Serge E. Hallyn 2017-06-02 16:02 ` Matt Brown 2017-06-02 16:02 ` Matt Brown 2017-06-02 16:02 ` Matt Brown 2017-06-02 16:57 ` Serge E. Hallyn 2017-06-02 16:57 ` Serge E. Hallyn 2017-06-02 16:57 ` Serge E. Hallyn 2017-06-02 16:57 ` Serge E. Hallyn 2017-06-02 17:32 ` Matt Brown 2017-06-02 17:32 ` Matt Brown 2017-06-02 17:32 ` Matt Brown 2017-06-02 18:18 ` Serge E. Hallyn 2017-06-02 18:18 ` Serge E. Hallyn 2017-06-02 18:18 ` Serge E. Hallyn 2017-06-02 18:18 ` Serge E. Hallyn 2017-06-02 19:22 ` Matt Brown 2017-06-02 19:22 ` Matt Brown 2017-06-02 19:22 ` Matt Brown 2017-06-02 19:25 ` Kees Cook 2017-06-02 19:25 ` Kees Cook 2017-06-02 19:25 ` Kees Cook 2017-06-02 19:25 ` Kees Cook 2017-06-02 19:26 ` Matt Brown 2017-06-02 19:26 ` Matt Brown 2017-06-02 19:26 ` Matt Brown 2017-06-02 19:26 ` Matt Brown 2017-06-02 20:05 ` Alan Cox 2017-06-02 20:05 ` Alan Cox 2017-06-02 20:05 ` Alan Cox 2017-06-02 20:11 ` Nick Kralevich 2017-06-02 20:11 ` Nick Kralevich 2017-06-02 20:11 ` Nick Kralevich 2017-06-02 20:46 ` Matt Brown 2017-06-02 20:46 ` Matt Brown 2017-06-02 20:46 ` Matt Brown 2017-06-03 22:00 ` Alan Cox 2017-06-03 22:00 ` Alan Cox 2017-06-03 22:00 ` Alan Cox 2017-06-03 22:22 ` Matt Brown 2017-06-03 22:22 ` Matt Brown 2017-06-03 22:22 ` Matt Brown 2017-06-04 3:37 ` Peter Dolding 2017-06-04 3:37 ` Peter Dolding 2017-06-04 3:37 ` Peter Dolding 2017-05-30 15:20 ` Casey Schaufler 2017-05-30 15:20 ` Casey Schaufler 2017-05-30 16:09 ` Matt Brown 2017-05-30 16:09 ` Matt Brown 2017-06-04 6:29 ` Boris Lukashev 2017-06-04 6:29 ` Boris Lukashev 2017-05-31 2:48 ` James Morris 2017-05-31 2:48 ` James Morris 2017-05-31 4:10 ` Matt Brown 2017-05-31 4:10 ` Matt Brown 2017-05-30 0:15 ` Matt Brown 2017-05-30 0:15 ` [kernel-hardening] " Matt Brown 2017-05-30 0:15 ` Matt Brown
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