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

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Date:   Mon, 6 May 2019 08:42:30 -0700
From:   Stephen Hemminger <stephen@...workplumber.org>
To:     Zhiqiang Liu <liuzhiqiang26@...wei.com>
Cc:     <liuhangbin@...il.com>, <kuznet@....inr.ac.ru>,
        <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: Re: [PATCH iproute2 v3] ipnetns: use-after-free problem in
 get_netnsid_from_name func

On Sat, 4 May 2019 15:26:25 +0800
Zhiqiang Liu <liuzhiqiang26@...wei.com> wrote:

> 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>

Applied. You can get better and more detailed checks by running with
valgrind. Which is what I did after applying your patch.