Date: Mon, 29 May 2017 23:26:40 +0100 From: Alan Cox <gnomes@...rguk.ukuu.org.uk> To: Matt Brown <matt@...tt.com> Cc: gregkh@...uxfoundation.org, serge@...lyn.com, keescook@...omium.org, kernel-hardening@...ts.openwall.com, linux-security-module@...r.kernel.org, linux-kernel@...r.kernel.org Subject: Re: [PATCH v7 2/2] security: tty: make TIOCSTI ioctl require CAP_SYS_ADMIN On Mon, 29 May 2017 17:38:00 -0400 Matt Brown <matt@...tt.com> wrote: > This introduces the tiocsti_restrict sysctl, whose default is controlled > via CONFIG_SECURITY_TIOCSTI_RESTRICT. When activated, this control > restricts all TIOCSTI ioctl calls from non CAP_SYS_ADMIN users. Which is really quite pointless as I keep pointing out and you keep reposting this nonsense. > > This patch depends on patch 1/2 > > This patch was inspired from GRKERNSEC_HARDEN_TTY. > > This patch would have prevented > https://bugzilla.redhat.com/show_bug.cgi?id=1411256 under the following > conditions: > * non-privileged container > * container run inside new user namespace And assuming no other ioctl could be used in an attack. Only there are rather a lot of ways an app with access to a tty can cause mischief if it's the same controlling tty as the higher privileged context that launched it. Properly written code allocates a new pty/tty pair for the lower privileged session. If the code doesn't do that then your change merely modifies the degree of mayhem it can cause. If it does it right then your patch is pointless. > Possible effects on userland: > > There could be a few user programs that would be effected by this > change. In other words, it's yet another weird config option that breaks stuff. NAK v7. Alan
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