netdev - [PATCH iproute2] iproute2: fix use-after-free

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Date:   Wed, 12 Sep 2018 16:29:28 -0700
From:   Mahesh Bandewar <mahesh@...dewar.net>
To:     Stephen Hemminger <stephen@...workplumber.org>
Cc:     netdev <netdev@...r.kernel.org>,
        Mahesh Bandewar <maheshb@...gle.com>
Subject: [PATCH iproute2] iproute2: fix use-after-free

From: Mahesh Bandewar <maheshb@...gle.com>

A local program using iproute2 lib pointed out the issue and looking
at the code it is pretty obvious -

    a = (struct nlmsghdr *)b;
    ...
    free(b);
    if (a->nlmsg_seq == seq)
    ...

Fixes: 86bf43c7c2fd ("lib/libnetlink: update rtnl_talk to support malloc buff at run time")
Signed-off-by: Mahesh Bandewar <maheshb@...gle.com>
---
 lib/libnetlink.c | 15 +++++++++++----
 1 file changed, 11 insertions(+), 4 deletions(-)

diff --git a/lib/libnetlink.c b/lib/libnetlink.c
index 928de1dd16d8..016a5f0bcfb6 100644
--- a/lib/libnetlink.c
+++ b/lib/libnetlink.c
@@ -661,17 +661,24 @@ next:
 				if (l < sizeof(struct nlmsgerr)) {
 					fprintf(stderr, "ERROR truncated\n");
 				} else if (!err->error) {
+					unsigned int tmp_seq;
+
 					/* check messages from kernel */
 					nl_dump_ext_ack(h, errfn);
 
-					if (answer)
+					tmp_seq = h->nlmsg_seq;
+					if (answer) {
 						*answer = (struct nlmsghdr *)buf;
-					else
+					} else {
 						free(buf);
-					if (h->nlmsg_seq == seq)
+						buf = NULL;
+					}
+					if (tmp_seq == seq) {
 						return 0;
-					else if (i < iovlen)
+					} else if (i < iovlen) {
+						free(buf);
 						goto next;
+					}
 					return 0;
 				}
 
-- 
2.19.0.rc2.392.g5ba43deb5a-goog