netdev - Re: [PATCH net-next v2 1/5] udp_tunnel: properly deal with xfrm gro encap.

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Message-ID: <67dd94e315ec3_14b1402947e@willemb.c.googlers.com.notmuch>
Date: Fri, 21 Mar 2025 12:33:39 -0400
From: Willem de Bruijn <willemdebruijn.kernel@...il.com>
To: Paolo Abeni <pabeni@...hat.com>, 
 netdev@...r.kernel.org
Cc: "David S. Miller" <davem@...emloft.net>, 
 Eric Dumazet <edumazet@...gle.com>, 
 Jakub Kicinski <kuba@...nel.org>, 
 Simon Horman <horms@...nel.org>, 
 Willem de Bruijn <willemdebruijn.kernel@...il.com>, 
 David Ahern <dsahern@...nel.org>, 
 Nathan Chancellor <nathan@...nel.org>
Subject: Re: [PATCH net-next v2 1/5] udp_tunnel: properly deal with xfrm gro
 encap.

Paolo Abeni wrote:
> The blamed commit below does not take in account that xfrm
> can enable GRO over UDP encapsulation without going through
> setup_udp_tunnel_sock().
> 
> At deletion time such socket will still go through
> udp_tunnel_cleanup_gro(), and the failed GRO type lookup will
> trigger the reported warning.
> 
> Add the GRO accounting for XFRM tunnel when GRO is enabled, and
> adjust the known gro types accordingly.
> 
> Note that we can't use setup_udp_tunnel_sock() here, as the xfrm
> tunnel setup can be "incremental" - e.g. the encapsulation is created
> first and GRO is enabled later.
> 
> Also we can not allow GRO sk lookup optimization for XFRM tunnels, as
> the socket could match the selection criteria at enable time, and
> later on the user-space could disconnect/bind it breaking such
> criteria.
> 
> Reported-by: syzbot+8c469a2260132cd095c1@...kaller.appspotmail.com
> Closes: https://syzkaller.appspot.com/bug?extid=8c469a2260132cd095c1
> Fixes: 311b36574ceac ("udp_tunnel: use static call for GRO hooks when possible")
> Signed-off-by: Paolo Abeni <pabeni@...hat.com>
> ---
> v1 -> v2:
>  - do proper account for xfrm, retain the warning
> ---
>  net/ipv4/udp.c         | 5 +++++
>  net/ipv4/udp_offload.c | 4 +++-
>  2 files changed, 8 insertions(+), 1 deletion(-)
> 
> diff --git a/net/ipv4/udp.c b/net/ipv4/udp.c
> index db606f7e41638..79efbf465fb04 100644
> --- a/net/ipv4/udp.c
> +++ b/net/ipv4/udp.c
> @@ -2903,10 +2903,15 @@ static void set_xfrm_gro_udp_encap_rcv(__u16 encap_type, unsigned short family,
>  {
>  #ifdef CONFIG_XFRM
>  	if (udp_test_bit(GRO_ENABLED, sk) && encap_type == UDP_ENCAP_ESPINUDP) {
> +		bool old_enabled = !!udp_sk(sk)->gro_receive;
> +
>  		if (family == AF_INET)
>  			WRITE_ONCE(udp_sk(sk)->gro_receive, xfrm4_gro_udp_encap_rcv);
>  		else if (IS_ENABLED(CONFIG_IPV6) && family == AF_INET6)
>  			WRITE_ONCE(udp_sk(sk)->gro_receive, ipv6_stub->xfrm6_gro_udp_encap_rcv);
> +
> +		if (!old_enabled && udp_sk(sk)->gro_receive)
> +			udp_tunnel_update_gro_rcv(sk, true);

The second part of the condition is always true right?