[PATCH iproute2 v4] ipnetns: use-after-free problem in get_netnsid_from_name func

[Zhiqiang Liu]

From: Zhiqiang Liu <liuzhiqian...@huawei.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 <kouhuiy...@huawei.com>
Signed-off-by: Zhiqiang Liu <liuzhiqian...@huawei.com>
Acked-by: Phil Sutter <p...@nwl.cc>
---
v3->v4: optimize code suggested by David Ahern
v2->v3: add Cc:netdev@vger.kernel.org suggested by Phil Sutter
v1->v2: correct commit log

 ip/ipnetns.c | 13 ++++++-------
 1 file changed, 6 insertions(+), 7 deletions(-)

diff --git a/ip/ipnetns.c b/ip/ipnetns.c
index 430d884..52aefac 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();

@@ -124,23 +124,22 @@ int get_netnsid_from_name(const char *name)

        /* Validate message and parse attributes */
        if (answer->nlmsg_type == NLMSG_ERROR)
-               goto err_out;
+               goto out;

        rthdr = NLMSG_DATA(answer);
        len = answer->nlmsg_len - NLMSG_SPACE(sizeof(*rthdr));
        if (len < 0)
-               goto err_out;
+               goto out;

        parse_rtattr(tb, NETNSA_MAX, NETNS_RTA(rthdr), len);

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

-err_out:
+out:
        free(answer);
-       return -1;
+       return ret;
 }

 struct nsid_cache {
-- 
1.8.3.1