mesg: remove ability to compile with fchmod(S_IWOTH)

The default is to use mesg(1) to modify write access for the "tty"
group, but there is an obscure legacy. If mesg(1) is compiled with the
option "--disable-use-tty-group", then it defaults to using
fchmod(S_IWGRP | S_IWOTH). This means that your tty is then writable
for everyone. Let's get rid of this ugly feature.

Reported-by: Chris Hofstaedtler <zeha@debian.org>
Signed-off-by: Karel Zak <kzak@redhat.com>

diff --git a/login-utils/login.1.adoc b/login-utils/login.1.adoc
index c31ec62696557fa04a58270a71af9d12f734f94b..fb4736c06307b80315268f9f8d8feabebe1c971b 100644 (file)
--- a/login-utils/login.1.adoc
+++ b/login-utils/login.1.adoc
@@ -97,13 +97,13 @@ Delay in seconds before being allowed another three tries after a login failure.
 
 *TTYPERM* (string)::
 
-The terminal permissions. The default value is _0600_ or _0620_ if tty group is used.
+The terminal permissions. The default value is _0600_ or _0620_ if tty group is used. See also *mesg*(1).
 
 *TTYGROUP* (string)::
 
 The login tty will be owned by the *TTYGROUP*. The default value is _tty_. If the *TTYGROUP* does not exist, then the ownership of the terminal is set to the user's primary group.
 +
-The *TTYGROUP* can be either the name of a group or a numeric group identifier.
+The *TTYGROUP* can be either the name of a group or a numeric group identifier. See also *mesg*(1).
 
 *HUSHLOGIN_FILE* (string)::
 

diff --git a/term-utils/mesg.1.adoc b/term-utils/mesg.1.adoc
index 81af64c71fd0e0655c483ad6e6406ed3b4e4ea08..df9adfd3801bbcb9d8ba182e50a45256a78f6a02 100644 (file)
--- a/term-utils/mesg.1.adoc
+++ b/term-utils/mesg.1.adoc
@@ -52,7 +52,23 @@ mesg - display (or do not display) messages from other users
 
 The *mesg* utility is invoked by a user to control write access others have to the terminal device associated with standard error output. If write access is allowed, then programs such as *talk*(1) and *write*(1) may display messages on the terminal.
 
-Traditionally, write access is allowed by default. However, as users become more conscious of various security risks, there is a trend to remove write access by default, at least for the primary login shell. To make sure your ttys are set the way you want them to be set, *mesg* should be executed in your login scripts.
+Traditionally, write access is allowed by default. However, as users become
+more conscious of various security risks, there is a trend to remove write
+access by default, at least for the primary login shell.
+
+The initial permissions for the terminal are set by *login*(1) according to TTYPERM
+and TTYGROUP from /etc/login.defs. The default is mode _0620_ if a tty group is used,
+and _0600_ without the group. The default tty group name is "tty".
+
+To ensure that your ttys are set in a portable and independent manner from system
+settings, *mesg* should be executed in your login scripts.
+
+*mesg* modifies the write permissions for a group on the current terminal
+device. Since version 2.41, *mesg* can no longer be compiled to make the
+terminal writable for _others_ and strictly modifies only _group_ permissions.
+The usual setup is to use a "tty" group and add relevant users to this group.
+Alternatively, a less secure solution is to set utilities like *write*(1) or
+*wall*(1) to setgid for the "tty" group.
 
 The *mesg* utility silently exits with error status 2 if not executed on a terminal. In this case executing *mesg* is pointless. The command line option *--verbose* forces *mesg* to print a warning in this situation. This behaviour has been introduced in version 2.33.
 
@@ -66,6 +82,7 @@ Allow messages to be displayed.
 
 If no arguments are given, *mesg* shows the current message status on standard error output.
 
+
 == OPTIONS
 
 *-v*, *--verbose*::

diff --git a/term-utils/mesg.c b/term-utils/mesg.c
index 23e2f0d0eba5375d0e8e96d475601539b9d645c3..3ff3b9e04a727df13fa37e3b313b69e7a6ff16da 100644 (file)
--- a/term-utils/mesg.c
+++ b/term-utils/mesg.c
@@ -157,11 +157,7 @@ int main(int argc, char *argv[])
 
        switch (rpmatch(argv[0])) {
        case RPMATCH_YES:
-#ifdef USE_TTY_GROUP
                if (fchmod(fd, sb.st_mode | S_IWGRP) < 0)
-#else
-               if (fchmod(fd, sb.st_mode | S_IWGRP | S_IWOTH) < 0)
-#endif
                        err(MESG_EXIT_FAILURE, _("change %s mode failed"), tty);
                if (verbose)
                        puts(_("write access to your terminal is allowed"));