On 22.05.19 21:15, Sasha Levin wrote:
> From: Eric Dumazet <edumazet@google.com>
> 
> [ Upstream commit 47d3d7fdb10a21c223036b58bd70ffdc24a472c4 ]
> 
> 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.

Just to let everybody know, while changing this has fixed the BUG_ON problem
while sending (in 4.4) it now crashes when releasing just a little later.
Still feels like the right direction but not complete, yet.

-Stefan

> 
> 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@google.com>
> Reported-by: Stefan Bader <stefan.bader@canonical.com>
> Cc: Peter Oskolkov <posk@google.com>
> Cc: Florian Westphal <fw@strlen.de>
> Signed-off-by: David S. Miller <davem@davemloft.net>
> Signed-off-by: Sasha Levin <sashal@kernel.org>
> ---
>  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 28aa9b30aecea..1f77fb4dc79df 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);
>  	spin_unlock(&fq->q.lock);
>  
>  	icmpv6_send(head, ICMPV6_TIME_EXCEED, ICMPV6_EXC_FRAGTIME, 0);
>