From 195624d9c26b64c6856863da30ec578a790feec4 Mon Sep 17 00:00:00 2001 From: Patrick Rohr Date: Tue, 20 Sep 2022 12:48:25 -0700 Subject: [PATCH] tun: support not enabling carrier in TUNSETIFF MIME-Version: 1.0 Content-Type: text/plain; charset=utf8 Content-Transfer-Encoding: 8bit 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 Cc: Maciej Żenczykowski Cc: Lorenzo Colitti Cc: Jason Wang Cc: Stephen Hemminger Cc: Nicolas Dichtel Reviewed-by: Maciej Żenczykowski Acked-by: Jason Wang Reviewed-by: Nicolas Dichtel Signed-off-by: David S. Miller --- drivers/net/tun.c | 9 ++++++--- include/uapi/linux/if_tun.h | 2 ++ 2 files changed, 8 insertions(+), 3 deletions(-) diff --git a/drivers/net/tun.c b/drivers/net/tun.c index 259b2b84b2b39..db736b944016e 100644 --- a/drivers/net/tun.c +++ b/drivers/net/tun.c @@ -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) { diff --git a/include/uapi/linux/if_tun.h b/include/uapi/linux/if_tun.h index 2ec07de1d73be..b6d7b868f2904 100644 --- a/include/uapi/linux/if_tun.h +++ b/include/uapi/linux/if_tun.h @@ -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 -- 2.30.2