From: Jann Horn <jannh@google.com>
To: Alan Cox <gnomes@lxorguk.ukuu.org.uk>
Cc: Matt Brown <matt@nmatt.com>,
serge@hallyn.com, jmorris@namei.org,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
jslaby@suse.com, Jonathan Corbet <corbet@lwn.net>,
Kees Cook <keescook@chromium.org>,
Andrew Morton <akpm@linux-foundation.org>,
kernel-hardening@lists.openwall.com,
linux-security-module@vger.kernel.org,
linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org
Subject: Re: [PATCH v5 0/2] security: tty: make TIOCSTI ioctl require CAP_SYS_ADMIN
Date: Tue, 25 Apr 2017 15:56:32 +0200 [thread overview]
Message-ID: <CAG48ez0uYkAg65iBZ8cKLxzFyEK=Axt=NP7jnmQkFp4rN=0GzA@mail.gmail.com> (raw)
In-Reply-To: <20170425144746.0d8721a3@lxorguk.ukuu.org.uk>
On Tue, Apr 25, 2017 at 3:47 PM, Alan Cox <gnomes@lxorguk.ukuu.org.uk> wrote:
>> There could be a few user programs that would be effected by this
>> change.
>> See: <https://codesearch.debian.net/search?q=ioctl%5C%28.*TIOCSTI>
>> notable programs are: agetty, csh, xemacs and tcsh
>>
>> However, I still believe that this change is worth it given that the
>> Kconfig defaults to n. This will be a feature that is turned on for the
>> same reason that people activate it when using grsecurity. Users of this
>> opt-in feature will realize that they are choosing security over some OS
>> features
>
> Only in this case they are not.
>
> If I am at the point I have the ability to send you TIOCSTI you already
> lost because I can just open /dev/tty to get access to my controlling tty
> and use write().
In terms of PTYs, this patch does not try to prevent writes to a slave
device (which afaik is what /dev/tty will give you). It tries to prevent the
equivalent of writes to the master device. As far as I know, there is no
way to go from a slave to the corresponding master without having
access to the master in some other way already.
WARNING: multiple messages have this Message-ID (diff)
From: jannh@google.com (Jann Horn)
To: linux-security-module@vger.kernel.org
Subject: [PATCH v5 0/2] security: tty: make TIOCSTI ioctl require CAP_SYS_ADMIN
Date: Tue, 25 Apr 2017 15:56:32 +0200 [thread overview]
Message-ID: <CAG48ez0uYkAg65iBZ8cKLxzFyEK=Axt=NP7jnmQkFp4rN=0GzA@mail.gmail.com> (raw)
In-Reply-To: <20170425144746.0d8721a3@lxorguk.ukuu.org.uk>
On Tue, Apr 25, 2017 at 3:47 PM, Alan Cox <gnomes@lxorguk.ukuu.org.uk> wrote:
>> There could be a few user programs that would be effected by this
>> change.
>> See: <https://codesearch.debian.net/search?q=ioctl%5C%28.*TIOCSTI>
>> notable programs are: agetty, csh, xemacs and tcsh
>>
>> However, I still believe that this change is worth it given that the
>> Kconfig defaults to n. This will be a feature that is turned on for the
>> same reason that people activate it when using grsecurity. Users of this
>> opt-in feature will realize that they are choosing security over some OS
>> features
>
> Only in this case they are not.
>
> If I am at the point I have the ability to send you TIOCSTI you already
> lost because I can just open /dev/tty to get access to my controlling tty
> and use write().
In terms of PTYs, this patch does not try to prevent writes to a slave
device (which afaik is what /dev/tty will give you). It tries to prevent the
equivalent of writes to the master device. As far as I know, there is no
way to go from a slave to the corresponding master without having
access to the master in some other way already.
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WARNING: multiple messages have this Message-ID (diff)
From: Jann Horn <jannh@google.com>
To: Alan Cox <gnomes@lxorguk.ukuu.org.uk>
Cc: Matt Brown <matt@nmatt.com>,
serge@hallyn.com, jmorris@namei.org,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
jslaby@suse.com, Jonathan Corbet <corbet@lwn.net>,
Kees Cook <keescook@chromium.org>,
Andrew Morton <akpm@linux-foundation.org>,
kernel-hardening@lists.openwall.com,
linux-security-module@vger.kernel.org,
linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org
Subject: [kernel-hardening] Re: [PATCH v5 0/2] security: tty: make TIOCSTI ioctl require CAP_SYS_ADMIN
Date: Tue, 25 Apr 2017 15:56:32 +0200 [thread overview]
Message-ID: <CAG48ez0uYkAg65iBZ8cKLxzFyEK=Axt=NP7jnmQkFp4rN=0GzA@mail.gmail.com> (raw)
In-Reply-To: <20170425144746.0d8721a3@lxorguk.ukuu.org.uk>
On Tue, Apr 25, 2017 at 3:47 PM, Alan Cox <gnomes@lxorguk.ukuu.org.uk> wrote:
>> There could be a few user programs that would be effected by this
>> change.
>> See: <https://codesearch.debian.net/search?q=ioctl%5C%28.*TIOCSTI>
>> notable programs are: agetty, csh, xemacs and tcsh
>>
>> However, I still believe that this change is worth it given that the
>> Kconfig defaults to n. This will be a feature that is turned on for the
>> same reason that people activate it when using grsecurity. Users of this
>> opt-in feature will realize that they are choosing security over some OS
>> features
>
> Only in this case they are not.
>
> If I am at the point I have the ability to send you TIOCSTI you already
> lost because I can just open /dev/tty to get access to my controlling tty
> and use write().
In terms of PTYs, this patch does not try to prevent writes to a slave
device (which afaik is what /dev/tty will give you). It tries to prevent the
equivalent of writes to the master device. As far as I know, there is no
way to go from a slave to the corresponding master without having
access to the master in some other way already.
next prev parent reply other threads:[~2017-04-25 13:57 UTC|newest]
Thread overview: 39+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-04-25 4:15 [PATCH v5 0/2] security: tty: make TIOCSTI ioctl require CAP_SYS_ADMIN Matt Brown
2017-04-25 4:15 ` [kernel-hardening] " Matt Brown
2017-04-25 4:15 ` Matt Brown
2017-04-25 4:15 ` [PATCH v5 1/2] security: tty: Add owner user namespace to tty_struct Matt Brown
2017-04-25 4:15 ` [kernel-hardening] " Matt Brown
2017-04-25 4:15 ` Matt Brown
2017-04-25 4:15 ` [PATCH v5 2/2] security: tty: make TIOCSTI ioctl require CAP_SYS_ADMIN Matt Brown
2017-04-25 4:15 ` [kernel-hardening] " Matt Brown
2017-04-25 4:15 ` Matt Brown
2017-04-25 13:47 ` [PATCH v5 0/2] " Alan Cox
2017-04-25 13:47 ` [kernel-hardening] " Alan Cox
2017-04-25 13:47 ` Alan Cox
2017-04-25 13:56 ` Jann Horn [this message]
2017-04-25 13:56 ` [kernel-hardening] " Jann Horn
2017-04-25 13:56 ` Jann Horn
2017-04-25 19:30 ` One Thousand Gnomes
2017-04-25 19:30 ` [kernel-hardening] " One Thousand Gnomes
2017-04-25 19:30 ` One Thousand Gnomes
2017-04-25 20:06 ` Jann Horn
2017-04-25 20:06 ` [kernel-hardening] " Jann Horn
2017-04-25 20:06 ` Jann Horn
2017-04-25 21:21 ` One Thousand Gnomes
2017-04-25 21:21 ` [kernel-hardening] " One Thousand Gnomes
2017-04-25 21:21 ` One Thousand Gnomes
2017-04-25 21:44 ` Jann Horn
2017-04-25 21:44 ` [kernel-hardening] " Jann Horn
2017-04-25 21:44 ` Jann Horn
2017-04-26 12:47 ` One Thousand Gnomes
2017-04-26 12:47 ` [kernel-hardening] " One Thousand Gnomes
2017-04-26 12:47 ` One Thousand Gnomes
2017-04-26 14:21 ` Matt Brown
2017-04-26 14:21 ` [kernel-hardening] " Matt Brown
2017-04-26 14:21 ` Matt Brown
2017-04-27 12:34 ` One Thousand Gnomes
2017-04-27 12:34 ` [kernel-hardening] " One Thousand Gnomes
2017-04-27 12:34 ` One Thousand Gnomes
2017-05-03 19:30 ` Kees Cook
2017-05-03 19:30 ` [kernel-hardening] " Kees Cook
2017-05-03 19:30 ` Kees Cook
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