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Subject[PATCH] TTY: do not update atime/mtime on read/write
Date
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.

Signed-off-by: Jiri Slaby <jslaby@suse.cz>
References: CVE-2013-0160
---
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 a86219c..8801385 100644
--- a/drivers/tty/tty_io.c
+++ b/drivers/tty/tty_io.c
@@ -980,8 +980,7 @@ 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;
}

@@ -1082,11 +1081,8 @@ 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;
--
1.8.1.2



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