Currently when device is moved between network namespaces using
RTM_NEWLINK message type and one of netns attributes (FLA_NET_NS_PID,
IFLA_NET_NS_FD, IFLA_TARGET_NETNSID) but w/o specifying IFLA_IFNAME, and
target namespace already has device with same name, userspace will get
EINVAL what is confusing and makes debugging harder.
Fix it so that userspace gets more appropriate EEXIST instead what makes
debugging much easier.
Before:
# ./ifname.sh
+ ip netns add ns0
+ ip netns exec ns0 ip link add l0 type dummy
+ ip netns exec ns0 ip link show l0
8: l0: <BROADCAST,NOARP> mtu 1500 qdisc noop state DOWN mode DEFAULT group default qlen 1000
link/ether 66:90:b5:d5:78:69 brd ff:ff:ff:ff:ff:ff
+ ip link add l0 type dummy
+ ip link show l0
10: l0: <BROADCAST,NOARP> mtu 1500 qdisc noop state DOWN mode DEFAULT group default qlen 1000
link/ether 6e:c6:1f:15:20:8d brd ff:ff:ff:ff:ff:ff
+ ip link set l0 netns ns0
RTNETLINK answers: Invalid argument
After:
# ./ifname.sh
+ ip netns add ns0
+ ip netns exec ns0 ip link add l0 type dummy
+ ip netns exec ns0 ip link show l0
8: l0: <BROADCAST,NOARP> mtu 1500 qdisc noop state DOWN mode DEFAULT group default qlen 1000
link/ether 1e:4a:72:e3:e3:8f brd ff:ff:ff:ff:ff:ff
+ ip link add l0 type dummy
+ ip link show l0
10: l0: <BROADCAST,NOARP> mtu 1500 qdisc noop state DOWN mode DEFAULT group default qlen 1000
link/ether f2:fc:fe:2b:7d:a6 brd ff:ff:ff:ff:ff:ff
+ ip link set l0 netns ns0
RTNETLINK answers: File exists
The problem is that do_setlink() passes its `char *ifname` argument,
that it gets from a caller, to __dev_change_net_namespace() as is (as
`const char *pat`), but semantics of ifname and pat can be different.
For example, __rtnl_newlink() does this:
net/core/rtnetlink.c
3270 char ifname[IFNAMSIZ];
...
3286 if (tb[IFLA_IFNAME])
3287 nla_strscpy(ifname, tb[IFLA_IFNAME], IFNAMSIZ);
3288 else
3289 ifname[0] = '\0';
...
3364 if (dev) {
...
3394 return do_setlink(skb, dev, ifm, extack, tb, ifname, status);
3395 }
, i.e. do_setlink() gets ifname pointer that is always valid no matter
if user specified IFLA_IFNAME or not and then do_setlink() passes this
ifname pointer as is to __dev_change_net_namespace() as pat argument.
But the pat (pattern) in __dev_change_net_namespace() is used as:
net/core/dev.c
11198 err = -EEXIST;
11199 if (__dev_get_by_name(net, dev->name)) {
11200 /* We get here if we can't use the current device name */
11201 if (!pat)
11202 goto out;
11203 err = dev_get_valid_name(net, dev, pat);
11204 if (err < 0)
11205 goto out;
11206 }
As the result the `goto out` path on line 11202 is neven taken and
instead of returning EEXIST defined on line 11198,
__dev_change_net_namespace() returns an error from dev_get_valid_name()
and this, in turn, will be EINVAL for ifname[0] = '\0' set earlier.
Fixes: d8a5ec6727 ("[NET]: netlink support for moving devices between network namespaces.")
Signed-off-by: Andrey Ignatov <rdna@fb.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
96a6b93b69