Bug#870638: systemd: /var/log/btmp has inconsistent permissions

[Mark Charter]

Michael,

Thanks for your reply.

/var/log/btmp should not be world readable because a common cause of
login failures is to give password instead of username, which would
result in passwords being world readable.  See Debian bug 341883:

https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=341883

sshd (from OpenSSH) will refuse to write to /var/log/btmp if it is world
readable.  This comment is from openssh/loginrec.c:

  /*
   * Logs failed login attempts in _PATH_BTMP if that exists.
   * The most common login failure is to give password instead of username.
   * So the _PATH_BTMP file checked for the correct permission, so that
   * only root can read it.
   */

I don't think /var/log/wtmp or /var/run/utmp record failed logins, so
they can be world readable.

Mark.

Michael Biebl writes:
 > Control: tags -1 + moreinfo
 > 
 > Am 03.08.2017 um 18:46 schrieb Mark Charter:
 > > Package: systemd
 > > Version: 232-25+deb9u1
 > > Severity: normal
 > > 
 > > Dear Maintainer,
 > > 
 > > When /var/log/btmp is created at installation (by
 > > /var/lib/dpkg/info/base-files.postinst) its permissions are 0660
 > > (u=rw,g=rw,o=).  When it is (re)created by log file rotation (in
 > > /etc/logrotate.conf) its permissions are also 0660.  But if it is
 > > created by systemd, or after a reboot, its permissions (from
 > > /usr/lib/tmpfiles.d/var.conf) are 0600.  So its permissions can change
 > > with time, and they often change across a reboot.
 > > 
 > > I suggest that the three sources of file permissions should be made
 > > consistent, for example by changing the permissions in
 > > /usr/lib/tmpfiles.d/var.conf from
 > > 
 > > f /var/log/btmp 0600 root utmp -
 > > 
 > > to
 > > 
 > > f /var/log/btmp 0660 root utmp -
 > 
 > Why do /var/log/btmp and /var/log/utmp have different permissions, i.e.
 > 0660 vs 0664 in Debian? That seems inconsistent as well.
 > 
 > 
 > -- 
 > Why is it that all of the instruments seeking intelligent life in the
 > universe are pointed away from Earth?
 > 
 > x[DELETED ATTACHMENT signature.asc, application/pgp-signature]