Re: [PATCH v2] who --mesg now checks the group of TTY devices

[Kamil Dudka]

On Friday 22 of January 2010 17:03:51 Jim Meyering wrote:
> Can you reproduce the situation in which this new configure-time
> option is required on e.g., Fedora 12?  So far, I haven't been able to,
> since all tty devices properly get the "tty" group, and in that
> case, the simple perm-comparison test is adequate.

What I am getting on a sane F-12 installation follows:

# ls -l /dev/tty?
crw--w----. 1 root root 4, 0 2010-01-22 18:48 /dev/tty0
crw--w----. 1 root root 4, 1 2010-01-22 18:48 /dev/tty1
crw--w----. 1 root tty  4, 2 2010-01-22 18:50 /dev/tty2
crw-------. 1 root root 4, 3 2010-01-22 18:48 /dev/tty3
crw-------. 1 root root 4, 4 2010-01-22 18:48 /dev/tty4
crw-------. 1 root root 4, 5 2010-01-22 18:48 /dev/tty5
crw-------. 1 root root 4, 6 2010-01-22 18:48 /dev/tty6
crw--w----. 1 root tty  4, 7 2010-01-22 18:48 /dev/tty7
crw--w----. 1 root tty  4, 8 2010-01-22 18:48 /dev/tty8
crw--w----. 1 root tty  4, 9 2010-01-22 18:48 /dev/tty9

> I realized that I didn't really remember the details,

Nor do I as wasn't anyhow involved in GNU coretuils when the issue
was discussed ;-)

> and NEWS didn't tell me enough, so started rewriting it:
>
>   who: the "+/-" --mesg (-T) indicator of whether a user/tty is accepting
>   messages could be incorrectly listed as "+", when in fact, the user was
>   not accepting messages (mesg no).  Before, who would examine only the
>   permission bits, and not consider the group of the TTY device file.
>   Thus, when a tty file's group would change somehow e.g., to "root",
>   that would make it unwritable (via write(1)) by normal users, in spite
>   of whatever the permission bits might imply.  Now, when configured
>   using the --with-tty-group[=NAME] option, who also compares the group
>   of the TTY device with NAME (or "tty" if no group name is specified).

> How can the group name change (or be set initially) to other than "tty"?
> I suspect this is an issue only on older systems.  If so, I need to
> say that in NEWS, rather than "somehow".

It looks like sort of default state to me.  To be frank, not sure if
intended and/or documented actually :-)

> Other than that, everything looks fine (I moved the "const").

I knew I had forgotten something.  Sorry about that.  It wasn't intentionally.

Kamil