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Date: Tue, 30 Apr 2024 14:28:22 -0400
From: Willem de Bruijn <willemdebruijn.kernel@gmail.com>
To: Richard Gobert <richardbgobert@gmail.com>, 
 davem@davemloft.net, 
 edumazet@google.com, 
 kuba@kernel.org, 
 pabeni@redhat.com, 
 dsahern@kernel.org, 
 willemdebruijn.kernel@gmail.com, 
 alobakin@pm.me, 
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Cc: Richard Gobert <richardbgobert@gmail.com>
Message-ID: <663138462a32e_32e7ba29458@willemb.c.googlers.com.notmuch>
In-Reply-To: <20240430143555.126083-2-richardbgobert@gmail.com>
References: <20240430143555.126083-1-richardbgobert@gmail.com>
 <20240430143555.126083-2-richardbgobert@gmail.com>
Subject: Re: [PATCH net v4 1/2] net: gro: fix udp bad offset in socket lookup
 by adding {inner_}network_offset to napi_gro_cb
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Richard Gobert wrote:
> Commits a602456 ("udp: Add GRO functions to UDP socket") and 57c67ff ("udp:
> additional GRO support") introduce incorrect usage of {ip,ipv6}_hdr in the
> complete phase of gro. The functions always return skb->network_header,
> which in the case of encapsulated packets at the gro complete phase, is
> always set to the innermost L3 of the packet. That means that calling
> {ip,ipv6}_hdr for skbs which completed the GRO receive phase (both in
> gro_list and *_gro_complete) when parsing an encapsulated packet's _outer_
> L3/L4 may return an unexpected value.
> 
> This incorrect usage leads to a bug in GRO's UDP socket lookup.
> udp{4,6}_lib_lookup_skb functions use ip_hdr/ipv6_hdr respectively. These
> *_hdr functions return network_header which will point to the innermost L3,
> resulting in the wrong offset being used in __udp{4,6}_lib_lookup with
> encapsulated packets.
> 
> This patch adds network_offset and inner_network_offset to napi_gro_cb, and
> makes sure both are set correctly.
> 
> To fix the issue, network_offsets union is used inside napi_gro_cb, in
> which both the outer and the inner network offsets are saved.
> 
> Reproduction example:
> 
> Endpoint configuration example (fou + local address bind)
> 
>     # ip fou add port 6666 ipproto 4
>     # ip link add name tun1 type ipip remote 2.2.2.1 local 2.2.2.2 encap fou encap-dport 5555 encap-sport 6666 mode ipip
>     # ip link set tun1 up
>     # ip a add 1.1.1.2/24 dev tun1
> 
> Netperf TCP_STREAM result on net-next before patch is applied:
> 
> net-next main, GRO enabled:
>     $ netperf -H 1.1.1.2 -t TCP_STREAM -l 5
>     Recv   Send    Send
>     Socket Socket  Message  Elapsed
>     Size   Size    Size     Time     Throughput
>     bytes  bytes   bytes    secs.    10^6bits/sec
> 
>     131072  16384  16384    5.28        2.37
> 
> net-next main, GRO disabled:
>     $ netperf -H 1.1.1.2 -t TCP_STREAM -l 5
>     Recv   Send    Send
>     Socket Socket  Message  Elapsed
>     Size   Size    Size     Time     Throughput
>     bytes  bytes   bytes    secs.    10^6bits/sec
> 
>     131072  16384  16384    5.01     2745.06
> 
> patch applied, GRO enabled:
>     $ netperf -H 1.1.1.2 -t TCP_STREAM -l 5
>     Recv   Send    Send
>     Socket Socket  Message  Elapsed
>     Size   Size    Size     Time     Throughput
>     bytes  bytes   bytes    secs.    10^6bits/sec
> 
>     131072  16384  16384    5.01     2877.38
> 
> Fixes: 57c67ff4bd92 ("udp: additional GRO support")
> Signed-off-by: Richard Gobert <richardbgobert@gmail.com>

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