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Commit b0de59b5733d18b0d1974a060860a8b5c1b36a2e

Authored by Jiri Slaby
Committed by Greg Kroah-Hartman
1 parent cb8081cb6b
Exists in smarc-l5.0.0_1.0.0-ga and in 5 other branches imx_3.10.17_1.0.1_ga, imx_3.10.53_1.1.0_ga, imx_3.14.28_1.0.0_ga, smarc-imx_3.10.53_1.1.0_ga, smarc-imx_3.14.28_1.0.0_ga

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>

Showing 1 changed file with 2 additions and 6 deletions Side-by-side Diff

drivers/tty/tty_io.c
Diff comments   View file @ b0de59b
... ... @@ -977,8 +977,7 @@
977 977 else
978 978 i = -EIO;
979 979 tty_ldisc_deref(ld);
980   - if (i > 0)
981   - inode->i_atime = current_fs_time(inode->i_sb);
  980 +
982 981 return i;
983 982 }
984 983  
985 984  
... ... @@ -1079,11 +1078,8 @@
1079 1078 break;
1080 1079 cond_resched();
1081 1080 }
1082   - if (written) {
1083   - struct inode *inode = file->f_path.dentry->d_inode;
1084   - inode->i_mtime = current_fs_time(inode->i_sb);
  1081 + if (written)
1085 1082 ret = written;
1086   - }
1087 1083 out:
1088 1084 tty_write_unlock(tty);
1089 1085 return ret;