From: Pali Rohár <pali@kernel.org> stable inclusion from linux-4.19.205 commit 0bc8d39791e65d2812746b6a07df4e1d482b7e08 -------------------------------- [ Upstream commit 2459dcb96bcba94c08d6861f8a050185ff301672 ] 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: Sasha Levin <sashal@kernel.org> Signed-off-by: Yang Yingliang <yangyingliang@huawei.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 1af47aaa7ba57..dc9de8731c564 100644 --- a/drivers/net/ppp/ppp_generic.c +++ b/drivers/net/ppp/ppp_generic.c @@ -1125,7 +1125,7 @@ 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); -- 2.25.1