From a33f669662b9a96da36c48b703eb5672209249d0 Mon Sep 17 00:00:00 2001

From: =?UTF-8?q?Pali=20Roh=C3=A1r?= <pali@kernel.org>

Date: Sat, 7 Aug 2021 15:27:03 +0200

Subject: [PATCH 3/7] ppp: Fix generating ifname when empty IFLA_IFNAME is

 specified

Git-commit: 2459dcb96bcba94c08d6861f8a050185ff301672

Patch-mainline: v5.14-rc6

References: git-fixes

IFLA_IFNAME is nul-term string which means that IFLA_IFNAME buffer can be

larger than length of string which contains.

Function __rtnl_newlink() generates new own ifname if either IFLA_IFNAME

was not specified at all or userspace passed empty nul-term string.

It is expected that if userspace does not specify ifname for new ppp netdev

then kernel generates one in format "ppp<id>" where id matches to the ppp

unit id which can be later obtained by PPPIOCGUNIT ioctl.

And it works in this way if IFLA_IFNAME is not specified at all. But it

does not work when IFLA_IFNAME is specified with empty string.

So fix this logic also for empty IFLA_IFNAME in ppp_nl_newlink() function

and correctly generates ifname based on ppp unit identifier if userspace

did not provided preferred ifname.

Without this patch when IFLA_IFNAME was specified with empty string then

kernel created a new ppp interface in format "ppp<id>" but id did not

match ppp unit id returned by PPPIOCGUNIT ioctl. In this case id was some

number generated by __rtnl_newlink() function.

Signed-off-by: Pali Rohár <pali@kernel.org>

Fixes: bb8082f69138 ("ppp: build ifname using unit identifier for rtnl based devices")

Signed-off-by: David S. Miller <davem@davemloft.net>

Signed-off-by: Denis Kirjanov <denis.kirjanov@suse.com>

---

 drivers/net/ppp/ppp_generic.c | 2 +-

 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/net/ppp/ppp_generic.c b/drivers/net/ppp/ppp_generic.c

index 352e751125fb..56b0bd90a9fb 100644

--- a/drivers/net/ppp/ppp_generic.c

+++ b/drivers/net/ppp/ppp_generic.c

@@ -1116,7 +1116,7 @@ static int ppp_nl_newlink(struct net *src_net, struct net_device *dev,

 	 * the PPP unit identifer as suffix (i.e. ppp<unit_id>). This allows

 	 * userspace to infer the device name using to the PPPIOCGUNIT ioctl.

 	 */

-	if (!tb[IFLA_IFNAME])

+	if (!tb[IFLA_IFNAME] || !nla_len(tb[IFLA_IFNAME]) || !*(char *)nla_data(tb[IFLA_IFNAME]))

 		conf.ifname_is_set = false;

 	err = ppp_dev_configure(src_net, dev, &conf;;

-- 

2.16.4