[Devel] [PATCH RHEL7 COMMIT] ms/tun: Add ioctl() TUNGETDEVNETNS cmd to allow obtaining real net ns of tun device

[Konstantin Khorenko]

The commit is pushed to "branch-rh7-3.10.0-1062.4.1.vz7.115.x-ovz" and will appear at https://src.openvz.org/scm/ovz/vzkernel.git
after rh7-3.10.0-1062.4.1.vz7.115.11
------>
commit dc787ea1cf38db66edbe23e7e8d08c546f49600a
Author: Alexander Mikhalitsyn <alexander.mikhalitsyn at virtuozzo.com>
Date:   Wed Nov 6 13:57:56 2019 +0300

    ms/tun: Add ioctl() TUNGETDEVNETNS cmd to allow obtaining real net ns of tun device
    
    In commit f2780d6d7475 "tun: Add ioctl() SIOCGSKNS cmd to allow
    obtaining net ns of tun device" it was missed that tun may change
    its net ns, while net ns of socket remains the same as it was
    created initially. SIOCGSKNS returns net ns of socket, so it is
    not suitable for obtaining net ns of device.
    
    We may have two tun devices with the same names in two net ns,
    and in this case it's not possible to determ, which of them
    fd refers to (TUNGETIFF will return the same name).
    
    This patch adds new ioctl() cmd for obtaining net ns of a device.
    
    Reported-by: Harald Albrecht <harald.albrecht at gmx.net>
    Signed-off-by: Kirill Tkhai <ktkhai at virtuozzo.com>
    Signed-off-by: David S. Miller <davem at davemloft.net>
    
    https://jira.sw.ru/browse/PSBM-99027
    (ported from commit 0c3e0e3bb623c3735b8c9ab8aa8332f944f83a9f)
    
    Signed-off-by: Alexander Mikhalitsyn <alexander.mikhalitsyn at virtuozzo.com>
    Acked-by: Cyrill Gorcunov <gorcunov at virtuozzo.com>
    Acked-by: Kirill Tkhai <ktkhai at virtuozzo.com>
---
 drivers/net/tun.c           | 10 ++++++++++
 include/uapi/linux/if_tun.h |  1 +
 2 files changed, 11 insertions(+)

diff --git a/drivers/net/tun.c b/drivers/net/tun.c
index e65ded4d1d10..d4c386671630 100644
--- a/drivers/net/tun.c
+++ b/drivers/net/tun.c
@@ -2326,6 +2326,7 @@ static long __tun_chr_ioctl(struct file *file, unsigned int cmd,
 	void __user* argp = (void __user*)arg;
 	unsigned int ifindex, carrier;
 	struct ifreq ifr;
+	struct net *net;
 	kuid_t owner;
 	kgid_t group;
 	int sndbuf;
@@ -2402,6 +2403,7 @@ static long __tun_chr_ioctl(struct file *file, unsigned int cmd,
 
 	tun_debug(KERN_INFO, tun, "tun_chr_ioctl cmd %u\n", cmd);
 
+	net = dev_net(tun->dev);
 	ret = 0;
 	switch (cmd) {
 	case TUNGETIFF:
@@ -2615,6 +2617,14 @@ static long __tun_chr_ioctl(struct file *file, unsigned int cmd,
 		ret = tun_net_change_carrier(tun->dev, (bool)carrier);
 		break;
 
+	case TUNGETDEVNETNS:
+		ret = -EPERM;
+		if (!ns_capable(net->user_ns, CAP_NET_ADMIN))
+			goto unlock;
+
+		ret = open_net_ns_fd(net);
+		break;
+
 	default:
 		ret = -EINVAL;
 		break;
diff --git a/include/uapi/linux/if_tun.h b/include/uapi/linux/if_tun.h
index af37bafdc36c..b24812331a17 100644
--- a/include/uapi/linux/if_tun.h
+++ b/include/uapi/linux/if_tun.h
@@ -57,6 +57,7 @@
 #define TUNSETVNETBE _IOW('T', 222, int)
 #define TUNGETVNETBE _IOR('T', 223, int)
 #define TUNSETCARRIER _IOW('T', 226, int)
+#define TUNGETDEVNETNS _IO('T', 227)
 
 /* CONFIG_VE_TUNTAP_ACCOUNTING should be set */
 #define TUNSETACCTID _IOW('T', 300, struct ifreq)