net: enable interface alias removal via rtnl

IFLA_IFALIAS is defined as NLA_STRING. It means that the minimal length of
the attribute is 1 ("\0"). However, to remove an alias, the attribute
length must be 0 (see dev_set_alias()).

Let's define the type to NLA_BINARY to allow 0-length string, so that the
alias can be removed.

Example:
$ ip l s dummy0 alias foo
$ ip l l dev dummy0
5: dummy0: <BROADCAST,NOARP> mtu 1500 qdisc noop state DOWN mode DEFAULT group default qlen 1000
    link/ether ae:20:30:4f:a7:f3 brd ff:ff:ff:ff:ff:ff
    alias foo

Before the patch:
$ ip l s dummy0 alias ""
RTNETLINK answers: Numerical result out of range

After the patch:
$ ip l s dummy0 alias ""
$ ip l l dev dummy0
5: dummy0: <BROADCAST,NOARP> mtu 1500 qdisc noop state DOWN mode DEFAULT group default qlen 1000
    link/ether ae:20:30:4f:a7:f3 brd ff:ff:ff:ff:ff:ff

CC: Oliver Hartkopp <oliver@hartkopp.net>
CC: Stephen Hemminger <stephen@networkplumber.org>
Fixes: 96ca4a2cc145 ("net: remove ifalias on empty given alias")
Reported-by: Julien FLoret <julien.floret@6wind.com>
Signed-off-by: Nicolas Dichtel <nicolas.dichtel@6wind.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/net/core/rtnetlink.c b/net/core/rtnetlink.c
index a6bcf86..5ace489 100644 (file)
--- a/net/core/rtnetlink.c
+++ b/net/core/rtnetlink.c
@@ -1483,7 +1483,10 @@ static const struct nla_policy ifla_policy[IFLA_MAX+1] = {
        [IFLA_LINKINFO]         = { .type = NLA_NESTED },
        [IFLA_NET_NS_PID]       = { .type = NLA_U32 },
        [IFLA_NET_NS_FD]        = { .type = NLA_U32 },
-       [IFLA_IFALIAS]          = { .type = NLA_STRING, .len = IFALIASZ-1 },
+       /* IFLA_IFALIAS is a string, but policy is set to NLA_BINARY to
+        * allow 0-length string (needed to remove an alias).
+        */
+       [IFLA_IFALIAS]          = { .type = NLA_BINARY, .len = IFALIASZ - 1 },
        [IFLA_VFINFO_LIST]      = {. type = NLA_NESTED },
        [IFLA_VF_PORTS]         = { .type = NLA_NESTED },
        [IFLA_PORT_SELF]        = { .type = NLA_NESTED },