Commit b0de59b5 authored Feb 15, 2013 by Jiri Slaby Committed by Greg Kroah-Hartman Feb 15, 2013

TTY: do not update atime/mtime on read/write

On http://vladz.devzero.fr/013_ptmx-timing.php

, we can see how to find
out length of a password using timestamps of /dev/ptmx. It is
documented in "Timing Analysis of Keystrokes and Timing Attacks on
SSH". To avoid that problem, do not update time when reading
from/writing to a TTY.

I am afraid of regressions as this is a behavior we have since 0.97
and apps may expect the time to be current, e.g. for monitoring
whether there was a change on the TTY. Now, there is no change. So
this would better have a lot of testing before it goes upstream.

References: CVE-2013-0160

Signed-off-by: Jiri Slaby <jslaby@suse.cz>
Cc: stable <stable@vger.kernel.org> # after 3.9 is out
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

parent cb8081cb

drivers/tty/tty_io.c

+2 −6

Original line number	Diff line number	Diff line
		@@ -977,8 +977,7 @@ static ssize_t tty_read(struct file file, char __user buf, size_t count,
		else
		i = -EIO;
		tty_ldisc_deref(ld);
		if (i > 0)
		inode->i_atime = current_fs_time(inode->i_sb);

		return i;
		}

		@@ -1079,11 +1078,8 @@ static inline ssize_t do_tty_write(
		break;
		cond_resched();
		}
		if (written) {
		struct inode *inode = file->f_path.dentry->d_inode;
		inode->i_mtime = current_fs_time(inode->i_sb);
		if (written)
		ret = written;
		}
		out:
		tty_write_unlock(tty);
		return ret;