netdev - Re: [PATCH net] ip6: fix skb leak in ip6frag_expire_frag

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Date:   Fri, 3 May 2019 08:33:28 -0700
From:   Peter Oskolkov <posk@...gle.com>
To:     Eric Dumazet <edumazet@...gle.com>
Cc:     "David S . Miller" <davem@...emloft.net>,
        netdev <netdev@...r.kernel.org>,
        Eric Dumazet <eric.dumazet@...il.com>,
        Stfan Bader <stefan.bader@...onical.com>,
        Florian Westphal <fw@...len.de>
Subject: Re: [PATCH net] ip6: fix skb leak in ip6frag_expire_frag_queue()

On Fri, May 3, 2019 at 4:47 AM Eric Dumazet <edumazet@...gle.com> wrote:
>
> Since ip6frag_expire_frag_queue() now pulls the head skb
> from frag queue, we should no longer use skb_get(), since
> this leads to an skb leak.
>
> Stefan Bader initially reported a problem in 4.4.stable [1] caused
> by the skb_get(), so this patch should also fix this issue.
>
> 296583.091021] kernel BUG at /build/linux-6VmqmP/linux-4.4.0/net/core/skbuff.c:1207!
> [296583.091734] Call Trace:
> [296583.091749]  [<ffffffff81740e50>] __pskb_pull_tail+0x50/0x350
> [296583.091764]  [<ffffffff8183939a>] _decode_session6+0x26a/0x400
> [296583.091779]  [<ffffffff817ec719>] __xfrm_decode_session+0x39/0x50
> [296583.091795]  [<ffffffff818239d0>] icmpv6_route_lookup+0xf0/0x1c0
> [296583.091809]  [<ffffffff81824421>] icmp6_send+0x5e1/0x940
> [296583.091823]  [<ffffffff81753238>] ? __netif_receive_skb+0x18/0x60
> [296583.091838]  [<ffffffff817532b2>] ? netif_receive_skb_internal+0x32/0xa0
> [296583.091858]  [<ffffffffc0199f74>] ? ixgbe_clean_rx_irq+0x594/0xac0 [ixgbe]
> [296583.091876]  [<ffffffffc04eb260>] ? nf_ct_net_exit+0x50/0x50 [nf_defrag_ipv6]
> [296583.091893]  [<ffffffff8183d431>] icmpv6_send+0x21/0x30
> [296583.091906]  [<ffffffff8182b500>] ip6_expire_frag_queue+0xe0/0x120
> [296583.091921]  [<ffffffffc04eb27f>] nf_ct_frag6_expire+0x1f/0x30 [nf_defrag_ipv6]
> [296583.091938]  [<ffffffff810f3b57>] call_timer_fn+0x37/0x140
> [296583.091951]  [<ffffffffc04eb260>] ? nf_ct_net_exit+0x50/0x50 [nf_defrag_ipv6]
> [296583.091968]  [<ffffffff810f5464>] run_timer_softirq+0x234/0x330
> [296583.091982]  [<ffffffff8108a339>] __do_softirq+0x109/0x2b0
>
> Fixes: d4289fcc9b16 ("net: IP6 defrag: use rbtrees for IPv6 defrag")
> Signed-off-by: Eric Dumazet <edumazet@...gle.com>
> Reported-by: Stfan Bader <stefan.bader@...onical.com>
> Cc: Peter Oskolkov <posk@...gle.com>
> Cc: Florian Westphal <fw@...len.de>
> ---
>  include/net/ipv6_frag.h | 1 -
>  1 file changed, 1 deletion(-)
>
> diff --git a/include/net/ipv6_frag.h b/include/net/ipv6_frag.h
> index 28aa9b30aeceac9a86ee6754e4b5809be115e947..1f77fb4dc79df6bc4e41d6d2f4d49ace32082ca4 100644
> --- a/include/net/ipv6_frag.h
> +++ b/include/net/ipv6_frag.h
> @@ -94,7 +94,6 @@ ip6frag_expire_frag_queue(struct net *net, struct frag_queue *fq)
>                 goto out;
>
>         head->dev = dev;
> -       skb_get(head);

This skb_get was introduced by commit 05c0b86b9696802fd0ce5676a92a63f1b455bdf3
"ipv6: frags: rewrite ip6_expire_frag_queue()", and the rbtree patch
is not in 4.4, where the bug is reported at.
Shouldn't the "Fixes" tag also reference the original patch?


>         spin_unlock(&fq->q.lock);
>
>         icmpv6_send(head, ICMPV6_TIME_EXCEED, ICMPV6_EXC_FRAGTIME, 0);
> --
> 2.21.0.1020.gf2820cf01a-goog
>