[Devel] [PATCH RH7 30/32] tun: Add ioctl() SIOCGSKNS cmd to allow obtaining net ns of tun device

[Pavel Tikhomirov]

From: Kirill Tkhai <ktkhai at virtuozzo.com>

This patch adds possibility to get tun device's net namespace fd
in the same way we allow to do that for sockets.

Socket ioctl numbers do not intersect with tun-specific, and there
is already SIOCSIFHWADDR used in tun code. So, SIOCGSKNS number
is choosen instead of custom-made for this functionality.

Note, that open_related_ns() uses plain get_net_ns() and it's safe
(net can't be already dead at this moment):

  tun socket is allocated via sk_alloc() with zero last arg (kern = 0).
  So, each alive socket increments net::count, and the socket is definitely
  alive during ioctl syscall.

Also, common variable net is introduced, so small cleanup in TUNSETIFF
is made.

Signed-off-by: Kirill Tkhai <ktkhai at virtuozzo.com>
Signed-off-by: David S. Miller <davem at davemloft.net>

While on it also fix inconsistency with MS behaviour: TUNSETIFF should
return EEXIST if tun exists.

(cherry picked from commit f2780d6d74756bc1d7ba32ff3dd0de4afd7c7e1e)

https://jira.sw.ru/browse/PSBM-102357

Signed-off-by: Pavel Tikhomirov <ptikhomirov at virtuozzo.com>
---
 drivers/net/tun.c | 18 ++++++++++++++++--
 1 file changed, 16 insertions(+), 2 deletions(-)

diff --git a/drivers/net/tun.c b/drivers/net/tun.c
index 81b305abbf05..08332bdff1bc 100644
--- a/drivers/net/tun.c
+++ b/drivers/net/tun.c
@@ -71,6 +71,7 @@
 #include <net/sock.h>
 #include <linux/skb_array.h>
 #include <linux/seq_file.h>
+#include <linux/socket.h>
 
 #include <asm/uaccess.h>
 
@@ -2329,6 +2330,7 @@ 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;
@@ -2338,7 +2340,7 @@ static long __tun_chr_ioctl(struct file *file, unsigned int cmd,
 	bool do_notify = false;
 
 	if (cmd == TUNSETIFF || cmd == TUNSETQUEUE || cmd == TUNSETACCTID ||
-			_IOC_TYPE(cmd) == 0x89) {
+	    (_IOC_TYPE(cmd) == 0x89 && cmd != SIOCGSKNS)) {
 		if (copy_from_user(&ifr, argp, ifreq_len))
 			return -EFAULT;
 	} else {
@@ -2365,7 +2367,11 @@ static long __tun_chr_ioctl(struct file *file, unsigned int cmd,
 #endif /* CONFIG_VE_TUNTAP_ACCOUNTING */
 
 	tun = __tun_get(tfile);
-	if (cmd == TUNSETIFF && !tun) {
+	net = sock_net(&tfile->sk);
+	if (cmd == TUNSETIFF) {
+		ret = -EEXIST;
+		if (tun)
+			goto unlock;
 		ifr.ifr_name[IFNAMSIZ-1] = '\0';
 
 		ret = tun_set_iff(tfile->net, file, &ifr);
@@ -2390,6 +2396,14 @@ static long __tun_chr_ioctl(struct file *file, unsigned int cmd,
 		tfile->ifindex = ifindex;
 		goto unlock;
 	}
+	if (cmd == SIOCGSKNS) {
+		ret = -EPERM;
+		if (!ns_capable(net->user_ns, CAP_NET_ADMIN))
+			goto unlock;
+
+		ret = open_related_ns(&net->ns, get_net_ns);
+		goto unlock;
+	}
 
 	ret = -EBADFD;
 	if (!tun)
-- 
2.24.1