netdev - [PATCH iproute2 v3] ipnetns: use-after-free problem in get_netnsid_from

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Date:   Sat, 4 May 2019 15:26:25 +0800
From:   Zhiqiang Liu <liuzhiqiang26@...wei.com>
To:     <stephen@...workplumber.org>, <liuhangbin@...il.com>,
        <kuznet@....inr.ac.ru>
CC:     <nicolas.dichtel@...nd.com>, <phil@....cc>,
        "wangxiaogang (F)" <wangxiaogang3@...wei.com>,
        Mingfangsen <mingfangsen@...wei.com>,
        "Zhoukang (A)" <zhoukang7@...wei.com>, <kouhuiying@...wei.com>,
        <netdev@...r.kernel.org>
Subject: [PATCH iproute2 v3] ipnetns: use-after-free problem in
 get_netnsid_from_name func

From: Zhiqiang Liu <liuzhiqiang26@...wei.com>

Follow the following steps:
# ip netns add net1
# export MALLOC_MMAP_THRESHOLD_=0
# ip netns list
then Segmentation fault (core dumped) will occur.

In get_netnsid_from_name func, answer is freed before rta_getattr_u32(tb[NETNSA_NSID]),
where tb[] refers to answer`s content. If we set MALLOC_MMAP_THRESHOLD_=0, mmap will
be adoped to malloc memory, which will be freed immediately after calling free func.
So reading tb[NETNSA_NSID] will access the released memory after free(answer).

Here, we will call get_netnsid_from_name(tb[NETNSA_NSID]) before free(answer).

Fixes: 86bf43c7c2f ("lib/libnetlink: update rtnl_talk to support malloc buff at run time")
Reported-by: Huiying Kou <kouhuiying@...wei.com>
Signed-off-by: Zhiqiang Liu <liuzhiqiang26@...wei.com>
Acked-by: Phil Sutter <phil@....cc>
---
v2->v3: add Cc:netdev@...r.kernel.org suggested by Phil Sutter
v1->v2: correct commit log

 ip/ipnetns.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/ip/ipnetns.c b/ip/ipnetns.c
index 430d884..d72be95 100644
--- a/ip/ipnetns.c
+++ b/ip/ipnetns.c
@@ -107,7 +107,7 @@ int get_netnsid_from_name(const char *name)
 	struct nlmsghdr *answer;
 	struct rtattr *tb[NETNSA_MAX + 1];
 	struct rtgenmsg *rthdr;
-	int len, fd;
+	int len, fd, ret = -1;

 	netns_nsid_socket_init();

@@ -134,8 +134,9 @@ int get_netnsid_from_name(const char *name)
 	parse_rtattr(tb, NETNSA_MAX, NETNS_RTA(rthdr), len);

 	if (tb[NETNSA_NSID]) {
+		ret = rta_getattr_u32(tb[NETNSA_NSID]);
 		free(answer);
-		return rta_getattr_u32(tb[NETNSA_NSID]);
+		return ret;
 	}

 err_out:
-- 
1.8.3.1