netdev - Re: net/ipv4: use-after-free in ipv4_datagram_support

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Message-ID: <CAF=yD-++XtWeaVmdhnrwiYLOG84JTMEuZr9mxyTRnde8vE7AFQ@mail.gmail.com>
Date:   Wed, 12 Apr 2017 11:39:16 -0400
From:   Willem de Bruijn <willemdebruijn.kernel@...il.com>
To:     Andrey Konovalov <andreyknvl@...gle.com>
Cc:     "David S. Miller" <davem@...emloft.net>,
        Alexey Kuznetsov <kuznet@....inr.ac.ru>,
        James Morris <jmorris@...ei.org>,
        Hideaki YOSHIFUJI <yoshfuji@...ux-ipv6.org>,
        Patrick McHardy <kaber@...sh.net>,
        netdev <netdev@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Cong Wang <xiyou.wangcong@...il.com>,
        Eric Dumazet <edumazet@...gle.com>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Kostya Serebryany <kcc@...gle.com>,
        syzkaller <syzkaller@...glegroups.com>
Subject: Re: net/ipv4: use-after-free in ipv4_datagram_support_cmsg

===================
> BUG: KASAN: use-after-free in ipv4_datagram_support_cmsg
> net/ipv4/ip_sockglue.c:500 [inline] at addr ffff880059be0128

Thanks for the report. This is accessing skb->dev from within recvmsg() at line

        info->ipi_ifindex = skb->dev->ifindex;

Introduced in 829ae9d61165 ("net-timestamp: allow reading recv cmsg on
errqueue with origin tstamp"). At this time the device may indeed have
gone away. I'm having a look at a way to read this in the receive BH
and store the ifindex.