netdev - Re: [Patch net v2] rtnetlink: fix double call of rtnl_link_get_net

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Message-ID: <20241130110734.354f73d7@kernel.org>
Date: Sat, 30 Nov 2024 11:07:34 -0800
From: Jakub Kicinski <kuba@...nel.org>
To: Cong Wang <xiyou.wangcong@...il.com>
Cc: netdev@...r.kernel.org, Cong Wang <cong.wang@...edance.com>,
 syzbot+21ba4d5adff0b6a7cfc6@...kaller.appspotmail.com, Kuniyuki Iwashima
 <kuniyu@...zon.com>
Subject: Re: [Patch net v2] rtnetlink: fix double call of
 rtnl_link_get_net_ifla()

On Fri, 29 Nov 2024 13:25:19 -0800 Cong Wang wrote:
> From: Cong Wang <cong.wang@...edance.com>
> 
> Currently rtnl_link_get_net_ifla() gets called twice when we create
> peer devices, once in rtnl_add_peer_net() and once in each ->newlink()
> implementation.
> 
> This looks safer, however, it leads to a classic Time-of-Check to
> Time-of-Use (TOCTOU) bug since IFLA_NET_NS_PID is very dynamic. And
> because of the lack of checking error pointer of the second call, it
> also leads to a kernel crash as reported by syzbot.
> 
> Fix this by getting rid of the second call, which already becomes
> redudant after Kuniyuki's work. We have to propagate the result of the
> first rtnl_link_get_net_ifla() down to each ->newlink().

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