Re: [PATCH] pps: require CAP_SYS_TIME to attach N_PPS ldisc

[Hungyu Lin]

> Are you sure this is stable material?

I added the stable tag because an unprivileged user can exhaust the
global source pool. I'll reassess it with the narrower fix.

> Did you check whether this breaks existing setups?

The check would reject that setup. The default capture settings can
be used without PPS_SETPARAMS, so that comparison was insufficient.

> Also, is pps_tty_open() called only from TIOCSETD?

No. Reopening an existing tty after hangup can reach it through
tty_ldisc_reinit(). The check would use the reopener's credentials
and could make open() fail with -EPERM.

> If pps_tty_dcd_change() is never
> called there, wouldn't refusing N_PPS on a pty be enough, leaving the
> real serial ports as they are today?

PTYs don't call dcd_change. Rejecting N_PPS on PTYs would block this
path and leave serial ports as they are.

Thanks,
Hungyu