[patch libnl] fix double free caused by freeing link af_data in rtnl_link_set_family()

[Jiri Pirko]

Introduced by commit 8026fe2e3a9089eff3f5a06ee6e3cc78d96334ed ("link:
Free and realloc af specific data upon rtnl_link_set_family()")

link->l_af_data[link->l_af_ops->ao_family] is freed here but not set to
zero. That leads to double free made by link_free_data->do_foreach_af.

Fix this by setting link->l_af_data[link->l_af_ops->ao_family] to zero
rigth after free.

Signed-off-by: Jiri Pirko <jiri at resnulli.us>
---
 lib/route/link.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/lib/route/link.c b/lib/route/link.c
index a73e1db..0bb90a0 100644
--- a/lib/route/link.c
+++ b/lib/route/link.c
@@ -1762,9 +1762,11 @@ void rtnl_link_set_family(struct rtnl_link *link, int family)
 	link->l_family = family;
 	link->ce_mask |= LINK_ATTR_FAMILY;
 
-	if (link->l_af_ops)
+	if (link->l_af_ops) {
 		af_free(link, link->l_af_ops,
 			link->l_af_data[link->l_af_ops->ao_family], NULL);
+		link->l_af_data[link->l_af_ops->ao_family] = NULL;
+	}
 
 	link->l_af_ops = af_lookup_and_alloc(link, family);
 }
-- 
1.8.3.1