From: Wolfram Gloger <wmglo@dent.med.uni-muenchen.de>
To: linux-kernel@vger.kernel.org
Subject: Re: [ 03/42] TTY: fix atime/mtime regression
In-Reply-To: <20130429184752.796052982@linuxfoundation.org>
References: <20130429184752.796052982@linuxfoundation.org>
CC: Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        wmglo@dent.med.uni-muenchen.de
Date: Tue, 30 Apr 2013 14:02:16 +0200
Message-ID: <u4k3nk6xbr.fsf@md.dent.med.uni-muenchen.de>
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Sender: linux-kernel-owner@vger.kernel.org
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Hi,

>To revert to the old behaviour while still preventing attackers to
>guess the password length, we update the timestamps in one-minute
>intervals by this patch.

Sorry if I miss something, but isn't this an issue that should be very
obviously fixed in user space?  Only user space knows whether the
atime/mtime updates on a device are security-sensitive or not.

The sshd process and/or the login process could easily perform randomly
timed, dummy utime() calls on the tty around and within the password
typing, making this attack unfeasible.  I faintly remember sshd _already
does this_ for the network packets anyway by exchanging dummy packets.

Regards,
Wolfram.
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