[PATCH iproute2] iplink_vrf: Save device index from response for return code

[dsahern@kernel.org]

From: David Ahern <dsahern@gmail.com>

A recent commit changed rtnl_talk_* to return the response message in
allocated memory so callers need to free it. The change to name_is_vrf
did not save the device index which is pointing to a struct inside the
now allocated and freed memory resulting in garbage getting returned
in some cases.

Fix by using a stack variable to save the return value and only set
it to ifi->ifi_index after all checks are done and before the answer
buffer is freed.

Fixes: 86bf43c7c2fdc ("lib/libnetlink: update rtnl_talk to support malloc buff at run time")
Cc: Hangbin Liu <liuhangbin@gmail.com>
Cc: Phil Sutter <phil@nwl.cc>
Signed-off-by: David Ahern <dsahern@gmail.com>
---
 ip/iplink_vrf.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/ip/iplink_vrf.c b/ip/iplink_vrf.c
index e9dd0df98412..6004bb4f305e 100644
--- a/ip/iplink_vrf.c
+++ b/ip/iplink_vrf.c
@@ -191,6 +191,7 @@ int name_is_vrf(const char *name)
 	struct rtattr *tb[IFLA_MAX+1];
 	struct rtattr *li[IFLA_INFO_MAX+1];
 	struct ifinfomsg *ifi;
+	int ifindex = 0;
 	int len;
 
 	addattr_l(&req.n, sizeof(req), IFLA_IFNAME, name, strlen(name) + 1);
@@ -218,7 +219,8 @@ int name_is_vrf(const char *name)
 	if (strcmp(RTA_DATA(li[IFLA_INFO_KIND]), "vrf"))
 		goto out;
 
+	ifindex = ifi->ifi_index;
 out:
 	free(answer);
-	return ifi->ifi_index;
+	return ifindex;
 }
-- 
2.11.0