linux-kernel - [PATCH 3.16 118/204] net: enable interface alias removal via rtnl

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Date:   Thu, 28 Dec 2017 17:05:44 +0000
From:   Ben Hutchings <ben@...adent.org.uk>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:     akpm@...ux-foundation.org, "David S. Miller" <davem@...emloft.net>,
        "Julien FLoret" <julien.floret@...nd.com>,
        "Nicolas Dichtel" <nicolas.dichtel@...nd.com>,
        "Stephen Hemminger" <stephen@...workplumber.org>,
        "Oliver Hartkopp" <oliver@...tkopp.net>
Subject: [PATCH 3.16 118/204] net: enable interface alias removal via rtnl

3.16.52-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Nicolas Dichtel <nicolas.dichtel@...nd.com>

commit 2459b4c635858094df78abb9ca87d99f89fe8ca5 upstream.

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@...tkopp.net>
CC: Stephen Hemminger <stephen@...workplumber.org>
Fixes: 96ca4a2cc145 ("net: remove ifalias on empty given alias")
Reported-by: Julien FLoret <julien.floret@...nd.com>
Signed-off-by: Nicolas Dichtel <nicolas.dichtel@...nd.com>
Signed-off-by: David S. Miller <davem@...emloft.net>
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 net/core/rtnetlink.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

--- a/net/core/rtnetlink.c
+++ b/net/core/rtnetlink.c
@@ -1187,7 +1187,10 @@ static const struct nla_policy ifla_poli
 	[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 },