netdev - [PATCH iproute2-next] libnetlink: fix use-after-free of message buf

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Message-Id: <1539031946-7908-1-git-send-email-vladbu@mellanox.com>
Date:   Mon,  8 Oct 2018 23:52:26 +0300
From:   Vlad Buslov <vladbu@...lanox.com>
To:     netdev@...r.kernel.org
Cc:     Vlad Buslov <vladbu@...lanox.com>
Subject: [PATCH iproute2-next] libnetlink: fix use-after-free of message buf

In __rtnl_talk_iov() main loop, err is a pointer to memory in dynamically
allocated 'buf' that is used to store netlink messages. If netlink message
is an error message, buf is deallocated before returning with error code.
However, on return err->error code is checked one more time to generate
return value, after memory which err points to has already been
freed. Save error code in temporary variable and use the variable to
generate return value.

Signed-off-by: Vlad Buslov <vladbu@...lanox.com>
---
 lib/libnetlink.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/lib/libnetlink.c b/lib/libnetlink.c
index f8b8fbfd0010..bc8338052e17 100644
--- a/lib/libnetlink.c
+++ b/lib/libnetlink.c
@@ -802,6 +802,7 @@ static int __rtnl_talk_iov(struct rtnl_handle *rtnl, struct iovec *iov,
 
 			if (h->nlmsg_type == NLMSG_ERROR) {
 				struct nlmsgerr *err = (struct nlmsgerr *)NLMSG_DATA(h);
+				int error = err->error;
 
 				if (l < sizeof(struct nlmsgerr)) {
 					fprintf(stderr, "ERROR truncated\n");
@@ -825,7 +826,7 @@ static int __rtnl_talk_iov(struct rtnl_handle *rtnl, struct iovec *iov,
 				else
 					free(buf);
 
-				return err->error ? -i : 0;
+				return error ? -i : 0;
 			}
 
 			if (answer) {
-- 
2.7.5