netdev - [iproute PATCH] ip-link: Fix use after free in nl_get_ll_addr

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Date:   Thu,  1 Mar 2018 10:35:12 +0100
From:   Phil Sutter <phil@....cc>
To:     Stephen Hemminger <stephen@...workplumber.org>
Cc:     netdev@...r.kernel.org
Subject: [iproute PATCH] ip-link: Fix use after free in nl_get_ll_addr_len()

Immediately after freeing the buffer returned from rtnl_talk(), it is
accessed again via pointer in struct rtattr array. This leads to some
builds not allowing to set an interface's MAC address because the
expected length value is garbage.

Fixes: 86bf43c7c2fdc ("lib/libnetlink: update rtnl_talk to support malloc buff at run time")
Signed-off-by: Phil Sutter <phil@....cc>
---
 ip/iplink.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/ip/iplink.c b/ip/iplink.c
index 230f4c5377d9f..d401311bcad9f 100644
--- a/ip/iplink.c
+++ b/ip/iplink.c
@@ -276,8 +276,9 @@ static int nl_get_ll_addr_len(unsigned int dev_index)
 		return -1;
 	}
 
+	len = RTA_PAYLOAD(tb[IFLA_ADDRESS]);
 	free(answer);
-	return RTA_PAYLOAD(tb[IFLA_ADDRESS]);
+	return len;
 }
 
 static void iplink_parse_vf_vlan_info(int vf, int *argcp, char ***argvp,
-- 
2.16.1