Debian bug report logs - #1545 `write' can't write to telnet logins Package: bsdutils? netstd? ; Reported by: Ian Jackson ; 27 days old. ----------------------------------------------------------------------- Message received at debian-bugs: From cus.cam.ac.uk!iwj10 Fri Oct 13 12:27:57 1995 Return-Path: Received: from pixar.com by mongo.pixar.com with smtp (Smail3.1.28.1 #15) id m0t3plt-000BHRC; Fri, 13 Oct 95 12:27 PDT Received: from bootes.cus.cam.ac.uk by pixar.com with SMTP id AA26183 (5.67b/IDA-1.5 for debian-bugs-pipe@mongo.pixar.com); Fri, 13 Oct 1995 12:27:32 -0700 Received: by bootes.cus.cam.ac.uk (Smail-3.1.29.0 #36) id m0t3pld-000BzhC; Fri, 13 Oct 95 20:27 BST Received: by chiark id (Debian /\oo/\ Smail3.1.29.1 #29.33); Fri, 13 Oct 95 20:14 BST Message-Id: Date: Fri, 13 Oct 95 20:14 BST From: Ian Jackson To: debian-bugs@pixar.com Subject: Re: Bug#1545: write' can't write, tty permissions In-Reply-To: <199510131700.SAA02571@i17linuxb.ists.pwr.wroc.pl> References: <199510131700.SAA02571@i17linuxb.ists.pwr.wroc.pl> Marek Michalkiewicz writes ("Re: Bug#1545: write' can't write, tty permissions"): > The problem is the "several other files" (because csh has its own file > incompatible with /etc/profile). Ideally there should be a shell script > executed by login instead of the login shell, which sets up environment, > mesg y/n, resource limits etc., and then does "exec - $SHELL". Unfortunately the chances of our being able to arrange this are nearly zero - there are far too many programs which just run the login shell directly. > > I still think that the default, as shipped, should be mesg y. > > Otherwise users will simply complain when they can't use talk &c. > > One problem with mesg y by default (this may be the reason why SCO > defaults to mesg n - it's C2, you know, even root can't log in if > anything is screwed up :-). Try to write to a user who is logging in > at the moment (mesg y by default, changed to mesg n later), and if you > succeed, don't exit write. You will still be able to write to that > user's terminal (because permissions are checked on open and never > later). This will cause trouble for PPP logins etc. > > Maybe I am too paranoid - this is not very likely to really happen, but > it is possible. I don't insist on mesg n (right now there are other, > more serious problems like /proc and the SAK not always guaranteed to > work), but I just want to mention one potential problem... This is a good point. Hmm, can we find those several files where `mesg y' would have to be set and set it there ? Ian. ----------------------------------------------------------------------- Acknowledgement sent to Ian Jackson : Extra info received and forwarded. Full text available. ----------------------------------------------------------------------- Information forwarded to debian-devel@pixar.com : Bug#1545 ; Package bsdutils? netstd? . Full text available. ----------------------------------------------------------------------- Message received at debian-bugs: From i17linuxb.ists.pwr.wroc.pl!marekm Fri Oct 13 10:01:27 1995 Return-Path: Received: from pixar.com by mongo.pixar.com with smtp (Smail3.1.28.1 #15) id m0t3nU7-000D0lC; Fri, 13 Oct 95 10:01 PDT Received: from i17linuxb.ists.pwr.wroc.pl by pixar.com with SMTP id AA13526 (5.67b/IDA-1.5 for debian-bugs-pipe@mongo.pixar.com); Fri, 13 Oct 1995 10:00:56 -0700 Received: (from marekm@localhost) by i17linuxb.ists.pwr.wroc.pl (8.6.12/8.6.9) id SAA02571; Fri, 13 Oct 1995 18:00:57 +0100 From: Marek Michalkiewicz Message-Id: <199510131700.SAA02571@i17linuxb.ists.pwr.wroc.pl> Subject: Re: Bug#1545: write' can't write, tty permissions To: iwj10@cus.cam.ac.uk (Ian Jackson) Date: Fri, 13 Oct 1995 18:00:54 +0100 (MET) Cc: debian-bugs@pixar.com In-Reply-To: from "Ian Jackson" at Oct 12, 95 02:15:00 pm X-Mailer: ELM [version 2.4 PL23] Content-Type: text Content-Length: 1359 Ian Jackson: > That would be nice. At the moment changing the local default for the > whole system means editing /etc/profile and several other files. I > suppose the xterm app-defaults could be used. The problem is the "several other files" (because csh has its own file incompatible with /etc/profile). Ideally there should be a shell script executed by login instead of the login shell, which sets up environment, mesg y/n, resource limits etc., and then does "exec - $SHELL". > I still think that the default, as shipped, should be mesg y. > Otherwise users will simply complain when they can't use talk &c. One problem with mesg y by default (this may be the reason why SCO defaults to mesg n - it's C2, you know, even root can't log in if anything is screwed up :-). Try to write to a user who is logging in at the moment (mesg y by default, changed to mesg n later), and if you succeed, don't exit write. You will still be able to write to that user's terminal (because permissions are checked on open and never later). This will cause trouble for PPP logins etc. Maybe I am too paranoid - this is not very likely to really happen, but it is possible. I don't insist on mesg n (right now there are other, more serious problems like /proc and the SAK not always guaranteed to work), but I just want to mention one potential problem... Marek ----------------------------------------------------------------------- Acknowledgement sent to Marek Michalkiewicz : Extra info received and forwarded. Full text available. ----------------------------------------------------------------------- Information forwarded to debian-devel@pixar.com : Bug#1545 ; Package bsdutils? netstd? . Full text available. ----------------------------------------------------------------------- Message received at debian-bugs: From cus.cam.ac.uk!iwj10 Thu Oct 12 11:12:33 1995 Return-Path: Received: from pixar.com by mongo.pixar.com with smtp (Smail3.1.28.1 #15) id m0t3S7N-000HXEC; Thu, 12 Oct 95 11:12 PDT Received: from bootes.cus.cam.ac.uk by pixar.com with SMTP id AA22108 (5.67b/IDA-1.5 for debian-bugs-pipe@mongo.pixar.com); Thu, 12 Oct 1995 11:12:03 -0700 Received: by bootes.cus.cam.ac.uk (Smail-3.1.29.0 #36) id m0t3S6H-000C00C; Thu, 12 Oct 95 19:11 BST Received: by chiark id (Debian /\oo/\ Smail3.1.29.1 #29.33); Thu, 12 Oct 95 14:15 BST Message-Id: Date: Thu, 12 Oct 95 14:15 BST From: Ian Jackson To: Marek Michalkiewicz Cc: debian-bugs@pixar.com Subject: Re: Bug#1545: write' can't write, tty permissions In-Reply-To: <199510121302.OAA28759@i17linuxb.ists.pwr.wroc.pl> References: <199510121302.OAA28759@i17linuxb.ists.pwr.wroc.pl> Marek Michalkiewicz writes ("Re: Bug#1545: write' can't write, tty permissions"): > Ian Jackson: > > IMO we should have getty, telnetd, login and xterm set the permissions > > to 620, making `mesg y' the default. The alternative is to have to > > try to find all the ways users get new tty's and try to find a way to > > make the default be `mesg y' in the /etc/* scripts. > > > > I don't think the default should be `mesg n'. > > Some systems (like SunOS) default to mesg y, others (like SCO) to mesg n. > Users can always change that in their .profile (or .csh.login, I think > this is the right name, I don't use csh...). This is a local issue - > ideally there should be some config file which can be edited to change > defaults like this without need to recompile everything. That would be nice. At the moment changing the local default for the whole system means editing /etc/profile and several other files. I suppose the xterm app-defaults could be used. I still think that the default, as shipped, should be mesg y. Otherwise users will simply complain when they can't use talk &c. Ian. ----------------------------------------------------------------------- Acknowledgement sent to Ian Jackson : Extra info received and forwarded. Full text available. ----------------------------------------------------------------------- Information forwarded to debian-devel@pixar.com : Bug#1545 ; Package bsdutils? netstd? . Full text available. ----------------------------------------------------------------------- Message received at debian-bugs: From i17linuxb.ists.pwr.wroc.pl!marekm Thu Oct 12 06:09:10 1995 Return-Path: Received: from pixar.com by mongo.pixar.com with smtp (Smail3.1.28.1 #15) id m0t3NNl-000GYGC; Thu, 12 Oct 95 06:09 PDT Received: from i17linuxb.ists.pwr.wroc.pl by pixar.com with SMTP id AA10198 (5.67b/IDA-1.5 for debian-bugs-pipe@mongo.pixar.com); Thu, 12 Oct 1995 06:08:41 -0700 Received: (from marekm@localhost) by i17linuxb.ists.pwr.wroc.pl (8.6.12/8.6.9) id OAA28759; Thu, 12 Oct 1995 14:02:56 +0100 From: Marek Michalkiewicz Message-Id: <199510121302.OAA28759@i17linuxb.ists.pwr.wroc.pl> Subject: Re: Bug#1545: write' can't write, tty permissions To: iwj10@cus.cam.ac.uk (Ian Jackson) Date: Thu, 12 Oct 1995 14:02:49 +0100 (MET) Cc: debian-bugs@pixar.com In-Reply-To: from "Ian Jackson" at Oct 12, 95 02:09:00 am X-Mailer: ELM [version 2.4 PL23] Content-Type: text Content-Length: 684 Ian Jackson: > IMO we should have getty, telnetd, login and xterm set the permissions > to 620, making `mesg y' the default. The alternative is to have to > try to find all the ways users get new tty's and try to find a way to > make the default be `mesg y' in the /etc/* scripts. > > I don't think the default should be `mesg n'. Some systems (like SunOS) default to mesg y, others (like SCO) to mesg n. Users can always change that in their .profile (or .csh.login, I think this is the right name, I don't use csh...). This is a local issue - ideally there should be some config file which can be edited to change defaults like this without need to recompile everything. Marek ----------------------------------------------------------------------- Acknowledgement sent to Marek Michalkiewicz : Extra info received and forwarded. Full text available. ----------------------------------------------------------------------- Information forwarded to debian-devel@pixar.com : Bug#1545 ; Package bsdutils? netstd? . Full text available. ----------------------------------------------------------------------- Message received at debian-bugs: From cus.cam.ac.uk!iwj10 Wed Oct 11 18:12:07 1995 Return-Path: Received: from pixar.com by mongo.pixar.com with smtp (Smail3.1.28.1 #15) id m0t3CBr-000GDpC; Wed, 11 Oct 95 18:12 PDT Received: from bootes.cus.cam.ac.uk by pixar.com with SMTP id AA19132 (5.67b/IDA-1.5 for debian-bugs-pipe@mongo.pixar.com); Wed, 11 Oct 1995 18:11:46 -0700 Received: by bootes.cus.cam.ac.uk (Smail-3.1.29.0 #36) id m0t3CBg-000BzMC; Thu, 12 Oct 95 02:11 BST Received: by chiark id (Debian /\oo/\ Smail3.1.29.1 #29.33); Thu, 12 Oct 95 02:09 BST Message-Id: Date: Thu, 12 Oct 95 02:09 BST From: Ian Jackson To: Marek Michalkiewicz , debian-bugs@pixar.com Subject: Re: Bug#1545: write' can't write, tty permissions Marek Michalkiewicz writes ("Bug#1545: write' can't write, tty permissions"): > I think write (and possibly wall if all users should be allowed to use it) > should be setgid tty. Making all tty devices world-writable is bad idea > IMHO. getty/telnetd/login should initially set permissions to 600, group > tty and "mesg y" should set them to 620. IMO we should have getty, telnetd, login and xterm set the permissions to 620, making `mesg y' the default. The alternative is to have to try to find all the ways users get new tty's and try to find a way to make the default be `mesg y' in the /etc/* scripts. I don't think the default should be `mesg n'. > BTW, getty sets tty perms to 622 (that's why miscutils is mentioned in > the Package: header). This is wrong (someone may open it before login > sets correct permissions), better use 600. Indeed. There's no reason for write &c to write to a terminal which has noone logged on and is waiting in getty. > I don't think making write setgid tty is more dangerous than making > tty devices world-writable. The tty group can't do anything more than > writing to "mesg y" terminals... Quite. Ian. ----------------------------------------------------------------------- Acknowledgement sent to Ian Jackson : Extra info received and forwarded. Full text available. ----------------------------------------------------------------------- Information forwarded to debian-devel@pixar.com : Bug#1545 ; Package bsdutils? netstd? . Full text available. ----------------------------------------------------------------------- Message received at debian-bugs: From i17linuxb.ists.pwr.wroc.pl!marekm Wed Oct 11 12:34:24 1995 Return-Path: Received: from pixar.com by mongo.pixar.com with smtp (Smail3.1.28.1 #15) id m0t36v2-000HkZC; Wed, 11 Oct 95 12:34 PDT Received: from i17linuxb.ists.pwr.wroc.pl by pixar.com with SMTP id AA03565 (5.67b/IDA-1.5 for debian-bugs-pipe@mongo.pixar.com); Wed, 11 Oct 1995 12:33:50 -0700 Received: (from marekm@localhost) by i17linuxb.ists.pwr.wroc.pl (8.6.12/8.6.9) id UAA25113 for debian-bugs@pixar.com; Wed, 11 Oct 1995 20:34:02 +0100 From: Marek Michalkiewicz Message-Id: <199510111934.UAA25113@i17linuxb.ists.pwr.wroc.pl> Subject: Bug#1545: `write' can't write, tty permissions To: debian-bugs@pixar.com Date: Wed, 11 Oct 1995 20:33:56 +0100 (MET) X-Mailer: ELM [version 2.4 PL23] Content-Type: text Content-Length: 723 Package: bsdutils, netstd, miscutils Version: bsdutils 1.3-1, netstd 1.17-1, miscutils 1.3-5 I think write (and possibly wall if all users should be allowed to use it) should be setgid tty. Making all tty devices world-writable is bad idea IMHO. getty/telnetd/login should initially set permissions to 600, group tty and "mesg y" should set them to 620. BTW, getty sets tty perms to 622 (that's why miscutils is mentioned in the Package: header). This is wrong (someone may open it before login sets correct permissions), better use 600. I don't think making write setgid tty is more dangerous than making tty devices world-writable. The tty group can't do anything more than writing to "mesg y" terminals... Marek ----------------------------------------------------------------------- Acknowledgement sent to Marek Michalkiewicz : Extra info received and forwarded. Full text available. ----------------------------------------------------------------------- Information forwarded to debian-devel@pixar.com : Bug#1545 ; Package bsdutils? netstd? . Full text available. ----------------------------------------------------------------------- Bug reopened, originator set to Ian Jackson . Request was from Ian Jackson to debian-bugs-request@pixar.com . Full text available. ----------------------------------------------------------------------- Message received at debian-bugs-done: From server.et-inf.fho-emden.de!tobias Mon Oct 9 17:24:53 1995 Return-Path: Received: from pixar.com by mongo.pixar.com with smtp (Smail3.1.28.1 #15) id m0t2SV2-000BghC; Mon, 9 Oct 95 17:24 PDT Received: from server.et-inf.fho-emden.de by pixar.com with SMTP id AA25655 (5.67b/IDA-1.5 for debian-bugs-done-pipe@mongo.pixar.com); Mon, 9 Oct 1995 17:24:29 -0700 Received: by server.et-inf.fho-emden.de (5.65/DEC-Ultrix/4.3) id AA02162; Tue, 10 Oct 1995 01:15:54 +0100 Message-Id: <9510100015.AA02162@server.et-inf.fho-emden.de> Subject: Re: Bug#1545: `write' can't write to telnet logins To: iwj10@cus.cam.ac.uk Date: Tue, 10 Oct 1995 01:15:53 +0100 (MET) From: "Peter Tobias" Cc: debian-bugs-done@pixar.com Reply-To: tobias@et-inf.fho-emden.de In-Reply-To: from "Ian Jackson" at Oct 4, 95 03:06:00 pm X-Mailer: ELM [version 2.4 PL23] Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 8bit Content-Length: 791 Ian Jackson wrote: > 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'). I changed telnetd. It will change the terminal to go+w. Peter -- Peter Tobias EMail: Fachhochschule Ostfriesland tobias@et-inf.fho-emden.de Fachbereich Elektrotechnik und Informatik tobias@perseus.fho-emden.de Constantiaplatz 4, 26723 Emden, Germany ----------------------------------------------------------------------- Notification sent to iwj10@cus.cam.ac.uk (Ian Jackson) : Bug acknowledged by developer. Full text available. ----------------------------------------------------------------------- Reply sent to tobias@et-inf.fho-emden.de : You have taken responsibility. Full text available. ----------------------------------------------------------------------- Message received at debian-bugs: From thor.cam.ac.uk!iwj10 Wed Oct 4 07:06:25 1995 Return-Path: Received: from pixar.com by mongo.pixar.com with smtp (Smail3.1.28.1 #15) id m0t0USn-000CxkC; Wed, 4 Oct 95 07:06 PDT Received: from hammer.thor.cam.ac.uk by pixar.com with SMTP id AA01184 (5.67b/IDA-1.5 for debian-bugs-pipe@mongo.pixar.com); Wed, 4 Oct 1995 07:06:02 -0700 Received: by hammer.thor.cam.ac.uk (Smail-3.1.29.0 #77) id m0t0USa-000JfBC; Wed, 4 Oct 95 15:06 BST Message-Id: Date: Wed, 4 Oct 95 15:06 BST Sender: iwj10@thor.cam.ac.uk (Ian Jackson) From: iwj10@cus.cam.ac.uk (Ian Jackson) To: debian-bugs@pixar.com Subject: `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. ----------------------------------------------------------------------- Acknowledgement sent to iwj10@cus.cam.ac.uk (Ian Jackson) : New bug report received and forwarded. Full text available. ----------------------------------------------------------------------- Report forwarded to debian-devel@pixar.com : Bug#1545 ; Package bsdutils? netstd? . Full text available. ----------------------------------------------------------------------- Ian Jackson / iwj10@thor.cam.ac.uk , with the debian-bugs tracking mechanism This page last modified 07:43:01 GMT Wed 01 Nov