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Date:   Sat, 4 May 2019 15:26:25 +0800
From:   Zhiqiang Liu <>
To:     <>, <>,
CC:     <>, <>,
        "wangxiaogang (F)" <>,
        Mingfangsen <>,
        "Zhoukang (A)" <>, <>,
Subject: [PATCH iproute2 v3] ipnetns: use-after-free problem in
 get_netnsid_from_name func

From: Zhiqiang Liu <>

Follow the following steps:
# ip netns add net1
# 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 <>
Signed-off-by: Zhiqiang Liu <>
Acked-by: Phil Sutter <>
v2->v3: add 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;


@@ -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]);
-		return rta_getattr_u32(tb[NETNSA_NSID]);
+		return ret;


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