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

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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>
This commit is contained in:
Jiri Slaby 2013-02-15 15:25:05 +01:00 committed by Greg Kroah-Hartman
parent cb8081cb6b
commit b0de59b573
1 changed files with 2 additions and 6 deletions
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8
drivers/tty/tty_io.c
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@ -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;