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    Subject[093/126] TTY: do not update atime/mtime on read/write
    3.6.11.3 stable review patch.
    If anyone has any objections, please let me know.

    ------------------

    From: Jiri Slaby <jslaby@suse.cz>

    [ Upstream commit b0de59b5733d18b0d1974a060860a8b5c1b36a2e ]

    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>
    Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
    ---
    drivers/tty/tty_io.c | 8 ++------
    1 file changed, 2 insertions(+), 6 deletions(-)

    diff --git a/drivers/tty/tty_io.c b/drivers/tty/tty_io.c
    index b425c79..e0767b7 100644
    --- a/drivers/tty/tty_io.c
    +++ b/drivers/tty/tty_io.c
    @@ -975,8 +975,7 @@ 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;
    }

    @@ -1077,11 +1076,8 @@ 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;
    --
    1.7.10.4



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