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tun: support not enabling carrier in TUNSETIFF

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This change adds support for not enabling carrier during TUNSETIFF
interface creation by specifying the IFF_NO_CARRIER flag.

Our tests make heavy use of tun interfaces. In some scenarios, the test
process creates the interface but another process brings it up after the
interface is discovered via netlink notification. In that case, it is
not possible to create a tun/tap interface with carrier off without it
racing against the bring up. Immediately setting carrier off via
TUNSETCARRIER is still too late.

Signed-off-by: Patrick Rohr <prohr@google.com>
Cc: Maciej Żenczykowski <maze@google.com>
Cc: Lorenzo Colitti <lorenzo@google.com>
Cc: Jason Wang <jasowang@redhat.com>
Cc: Stephen Hemminger <stephen@networkplumber.org>
Cc: Nicolas Dichtel <nicolas.dichtel@6wind.com>
Reviewed-by: Maciej Żenczykowski <maze@google.com>
Acked-by: Jason Wang <jasowang@redhat.com>
Reviewed-by: Nicolas Dichtel <nicolas.dichtel@6wind.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Patrick Rohr 2022-09-20 12:48:25 -07:00 committed by David S. Miller
parent 504c25cb76
commit 195624d9c2
2 changed files with 8 additions and 3 deletions
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9
drivers/net/tun.c
View File

@ -2828,7 +2828,10 @@ static int tun_set_iff(struct net *net, struct file *file, struct ifreq *ifr)
rcu_assign_pointer(tfile->tun, tun);
}
netif_carrier_on(tun->dev);
if (ifr->ifr_flags & IFF_NO_CARRIER)
netif_carrier_off(tun->dev);
else
netif_carrier_on(tun->dev);
/* Make sure persistent devices do not get stuck in
* xoff state.
@ -3056,8 +3059,8 @@ static long __tun_chr_ioctl(struct file *file, unsigned int cmd,
* This is needed because we never checked for invalid flags on
* TUNSETIFF.
*/
return put_user(IFF_TUN | IFF_TAP | TUN_FEATURES,
(unsigned int __user*)argp);
return put_user(IFF_TUN | IFF_TAP | IFF_NO_CARRIER |
TUN_FEATURES, (unsigned int __user*)argp);
} else if (cmd == TUNSETQUEUE) {
return tun_set_queue(file, &ifr);
} else if (cmd == SIOCGSKNS) {

2
include/uapi/linux/if_tun.h
View File

@ -67,6 +67,8 @@
#define IFF_TAP 0x0002
#define IFF_NAPI 0x0010
#define IFF_NAPI_FRAGS 0x0020
/* Used in TUNSETIFF to bring up tun/tap without carrier */
#define IFF_NO_CARRIER 0x0040
#define IFF_NO_PI 0x1000
/* This flag has no real effect */
#define IFF_ONE_QUEUE 0x2000