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Date: Mon, 17 Apr 2017 08:53:45 +0200
From: Greg KH <gregkh@...uxfoundation.org>
To: Matt Brown <matt@...tt.com>
Cc: jmorris@...ei.org, akpm@...ux-foundation.org,
linux-security-module@...r.kernel.org, linux-kernel@...r.kernel.org,
kernel-hardening@...ts.openwall.com
Subject: Re: [PATCH 3/4] restrict unprivileged TIOCSTI tty ioctl
On Mon, Apr 17, 2017 at 02:07:05AM -0400, Matt Brown wrote:
> this patch depends on patch 1 and 2
>
> enforces restrictions on unprivileged users injecting commands
> into other processes in the same tty session using the TIOCSTI ioctl
>
> Signed-off-by: Matt Brown <matt@...tt.com>
> ---
> drivers/tty/tty_io.c | 4 ++++
> 1 file changed, 4 insertions(+)
>
> diff --git a/drivers/tty/tty_io.c b/drivers/tty/tty_io.c
> index e6d1a65..31894e8 100644
> --- a/drivers/tty/tty_io.c
> +++ b/drivers/tty/tty_io.c
> @@ -2296,11 +2296,15 @@ static int tty_fasync(int fd, struct file *filp, int on)
> * FIXME: may race normal receive processing
> */
>
> +int tiocsti_restrict = IS_ENABLED(CONFIG_SECURITY_TIOCSTI_RESTRICT);
> +
> static int tiocsti(struct tty_struct *tty, char __user *p)
> {
> char ch, mbz = 0;
> struct tty_ldisc *ld;
>
> + if (tiocsti_restrict && !capable(CAP_SYS_ADMIN))
> + return -EPERM;
So, what type of "normal" userspace operations did you just break here?
What type of "not normal" did you break/change?
Why tie this to CAP_SYS_ADMIN as well? That wasn't listed in your
Kconfig help text. This seems like an additional capabilities
dependancy that odds are, most people do not want...
> if ((current->signal->tty != tty) && !capable(CAP_SYS_ADMIN))
> return -EPERM;
And finally, why doesn't this original check handle what you want to do
already?
I don't understand your "threat model" you wish to address by this
change series, please be a lot more explicit in your patch changelog
descriptions.
thanks,
greg k-h
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