Re: [PATCH] net: rtnl: avoid uninitialized data in IFLA_VF_VLAN_LIST handling

With the newly added support for IFLA_VF_VLAN_LIST netlink messages,
we get a warning about potential uninitialized variable use in
the parsing of the user input when enabling the -Wmaybe-uninitialized
warning:

net/core/rtnetlink.c: In function 'do_setvfinfo':
net/core/rtnetlink.c:1756:9: error: 'ivvl$' may be used uninitialized in this function [-Werror=maybe-uninitialized]

I have not been able to prove whether it is possible to arrive in
this code with an empty IFLA_VF_VLAN_LIST block, but if we do,
then ndo_set_vf_vlan gets called with uninitialized arguments.

This adds an explicit check for an empty list, making it obvious
to the reader and the compiler that this cannot happen.

Fixes: 79aab093a0b5 ("net: Update API for VF vlan protocol 802.1ad support")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
---
 net/core/rtnetlink.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/net/core/rtnetlink.c b/net/core/rtnetlink.c
index 3ac8946bf244..b06d2f46b83e 100644
--- a/net/core/rtnetlink.c
+++ b/net/core/rtnetlink.c

@@ -1753,6 +1753,9 @@ static int do_setvfinfo(struct net_device *dev, struct nlattr **tb)

                        len++;
                }
+               if (len == 0)
+                       return -EINVAL;
+
                err = ops->ndo_set_vf_vlan(dev, ivvl[0]->vf, ivvl[0]->vlan,
                                           ivvl[0]->qos, ivvl[0]->vlan_proto);
                if (err < 0)
--

2.9.0