16120 open("/dev/ppp", O_RDWR)          = -1 EPERM (Operation not permitted)

2.6.16-026test017
template: fc4
pppd (fc4):
-bash-3.1# rpm -qa | grep ppp
ppp-2.4.2-7

...
static int ppp_open(struct inode *inode, struct file *file)
{
        /*
         * This could (should?) be enforced by the permissions on /dev/ppp.
         */
        if (!capable(CAP_NET_ADMIN))
                return -EPERM;
        return 0;
}
...

[hw]# vzctl stop 35
Stopping VPS ...
VPS was stopped
VPS is unmounted
[hw]# vzctl set 35  --capability net_admin:on --save
Saved parameters for VPS 35
[hw]# vzctl start 35
Starting VPS ...
VPS is mounted
Setting CPU units: 1000
Setting devices
VPS start in progress...
[root@dhcp0-174 tmp]# vzctl enter 35
entered into VPS 35
-bash-3.1# pppd
pppd     pppdump
-bash-3.1# pppd
-bash-3.1# echo $?
1
-bash-3.1# pppd
-bash-3.1# echo $?
1

-bash-3.1# cat /var/log/messages | grep pppd
Sep 18 00:57:42 hw pppd[17673]: pppd 2.4.2 started by root, uid 0
Sep 18 00:57:42 hw pppd[17673]: Couldn't set tty to PPP discipline: Invalid argument
Sep 18 00:57:42 hw pppd[17673]: Exit.
Sep 18 01:12:23 hw pppd[20190]: pppd 2.4.2 started by root, uid 0
Sep 18 01:12:23 hw pppd[20190]: Failed to open /dev/pts/0: Device or resource busy
Sep 18 01:12:23 hw pppd[20190]: Exit.

    if (ioctl(tty_fd, TIOCSETD, &ppp_disc) < 0) {
        if ( ! ok_error (errno) ) {
            error("Couldn't set tty to PPP discipline: %m");
            return -1;
        }
    }

linuxsrc $ grep -r tty_register_ldisc ./ | grep N_PPP
./drivers/net/ppp_async.c:      err = tty_register_ldisc(N_PPP, &ppp_ldisc);
linuxsrc $ cat kernel-2.6.16-026test017-i686.config.ovz | grep CONFIG_PPP_ASYNC
CONFIG_PPP_ASYNC=m

[hw]# lsmod | grep ppp
ppp_generic            20620  0
slhc                    6240  1 ppp_generi
[root@dhcp0-174 ~]# modprobe ppp_async
[root@dhcp0-174 ~]# echo $?
0
[root@dhcp0-174 ~]# lsmod | grep ppp
ppp_async               8960  0
crc_ccitt               2048  1 ppp_async
ppp_generic            20620  1 ppp_async
slhc                    6240  1 ppp_generic

-bash-3.1# pppd
-bash-3.1# echo $?
1
-bash-3.1# tail -3 /var/log/messages
Sep 18 01:59:15 dhcp0-174 pppd[25632]: pppd 2.4.2 started by root, uid 0
Sep 18 01:59:15 dhcp0-174 pppd[25632]: Couldn't create new ppp unit: Operation not permitted
Sep 18 01:59:15 dhcp0-174 pppd[25632]: Exit.

25784 ioctl(10, PPPIOCNEWUNIT, 0x80083c08) = -1 EPERM (Operation not permitted)

PPP: couldn't register device ppp0 (-1)

        ret = register_netdev(dev);
        if (ret != 0) {
                printk(KERN_ERR "PPP: couldn't register device %s (%d)\n",
                       dev->name, ret);
                goto out2;
        }

        ret = -EPERM;
        if (!ve_is_super(get_exec_env()) && ve_is_dev_movable(dev))
                goto out;