Bug#1545: `write' can't write to telnet logins
Package: bsdutils? netstd?
Version: bsdutils 1.3-1, netstd 1.17-1
Are `mesg y' terminals on Debian supposed to be g+w, or go+w ?
telnetd (from netbase) and mesg (from bsdutils) seem to thing g+w
ought to be sufficient; however, write (also from bsdutils) seems to
require go+w (though `richard', who was writing to me in another
window at the time of the transcript below, didn't report that it
complained about his terminal being `mesg n').
Making write setgid tty may solve the problem, but such a decision
should only be taken after examining the code to make sure it's not a
security problem.
Ian.
[ Running in an xterm ... ]
chiark:~> finger
Login Name Tty Idle Login Time Office Office Phone
[...]
iwj10 Ian Jackson - unpriv p4 Oct 4 12:47 (ealingbroadway.c)
iwj10 Ian Jackson - unpriv p3 1:03 Oct 4 12:49 (ealingbroadway.c)
iwj10 Ian Jackson - unpriv p5 Oct 4 12:50 (ealingbroadway.c)
iwj10 Ian Jackson - unpriv p6 1:05 Oct 4 12:53 (ealingbroadway.c)
richard Richard Kettlewell *p0 Oct 4 10:05 (muskogee.elmail.)
richard Richard Kettlewell p7 Oct 4 12:59 (muskogee.elmail.)
chiark:~> write richard
write: /dev/ttyp7: Permission denied
chiark:~> ll /dev/ttyp7
crw--w---- 1 richard tty 4, 199 Oct 4 14:55 /dev/ttyp7
chiark:~> ls -al /usr/bin/write
-rwxr-xr-x 1 root root 12292 Jun 22 20:25 /usr/bin/write*
chiark:~> ytalk richard
chiark:~> ytalk -x richard
chiark:~> grep mesg /etc/profile
mesg y
chiark:~> tty
/dev/ttyp5
chiark:~> id
uid=1001(iwj10) gid=1001(iwj10) groups=1001(iwj10)
chiark:~> ll /dev/ttyp5
crw--w--w- 1 iwj10 iwj10 4, 197 Oct 4 15:01 /dev/ttyp5
chiark:~>
Trying 131.111.131.114...
Connected to chiark.chu.cam.ac.uk.
Escape character is '^]'.
Debian GNU/Linux 0.93
Copyright (C) 1994, 1995 Debian Association, Inc. and others
chiark login: iwj10
Password:
Last login: Wed Oct 4 12:31:00 on ttyc2
Copyright (C) 1994, 1995 Debian Association, Inc. and others
Linux chiark 1.2.13 #2 Sat Sep 30 11:40:37 BST 1995 i486
Unauthorised access prohibited; if you do not know that you are authorised
then you are not. See /info/rules.text for the rules for the use of
chiark, and /info/chiark.text for information about the system.
Recent items in /info/new - see the file for full details:
1) Problem with trn hanging believed fixed. (3.10.1995)
2) Default terminal message status is now `y'. (3.10.1995)
3) trn `l' (list groups) command should now work. (3.10.1995)
--------------------------------------------------
3:01pm up 4 days, 2:56, 8 users, load average: 0.48, 0.26, 0.09
chiark:~> tty
/dev/ttyp1
chiark:~> ll /dev/ttyp1
crw--w---- 1 iwj10 tty 4, 193 Oct 4 15:01 /dev/ttyp1
chiark:~> exit
exit
Connection closed by foreign host.
Reply to: