netdev - Re: [PATCH net v2 2/4] gro: fix ownership transfer

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Message-ID: <65f98f6faf355_11543d294d4@willemb.c.googlers.com.notmuch>
Date: Tue, 19 Mar 2024 09:13:19 -0400
From: Willem de Bruijn <willemdebruijn.kernel@...il.com>
To: Antoine Tenart <atenart@...nel.org>, 
 davem@...emloft.net, 
 kuba@...nel.org, 
 pabeni@...hat.com, 
 edumazet@...gle.com
Cc: Antoine Tenart <atenart@...nel.org>, 
 steffen.klassert@...unet.com, 
 willemdebruijn.kernel@...il.com, 
 netdev@...r.kernel.org
Subject: Re: [PATCH net v2 2/4] gro: fix ownership transfer

Antoine Tenart wrote:
> If packets are GROed with fraglist they might be segmented later on and
> continue their journey in the stack. In skb_segment_list those skbs can
> be reused as-is. This is an issue as their destructor was removed in
> skb_gro_receive_list but not the reference to their socket, and then
> they can't be orphaned. Fix this by also removing the reference to the
> socket.
> 
> For example this could be observed,
> 
>   kernel BUG at include/linux/skbuff.h:3131!  (skb_orphan)
>   RIP: 0010:ip6_rcv_core+0x11bc/0x19a0
>   Call Trace:
>    ipv6_list_rcv+0x250/0x3f0
>    __netif_receive_skb_list_core+0x49d/0x8f0
>    netif_receive_skb_list_internal+0x634/0xd40
>    napi_complete_done+0x1d2/0x7d0
>    gro_cell_poll+0x118/0x1f0
> 
> A similar construction is found in skb_gro_receive, apply the same
> change there.
> 
> Fixes: 5e10da5385d2 ("skbuff: allow 'slow_gro' for skb carring sock reference")
> Signed-off-by: Antoine Tenart <atenart@...nel.org>

Reviewed-by: Willem de Bruijn <willemb@...gle.com>

The BUG_ON in skb_orphan makes the invariant clear that the two fields
must be cleared together:

        if (skb->destructor) {
                skb->destructor(skb);
                skb->destructor = NULL;
                skb->sk         = NULL;
        } else {
                BUG_ON(skb->sk);
        }