Re: [PATCH net v4 1/2] net: gro: fix udp bad offset in socket lookup by adding {inner_}network_offset to napi_gro_cb

[Eric Dumazet]

On Tue, Apr 30, 2024 at 4:40 PM Richard Gobert <richardbgobert@xxxxxxxxx> 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")

Nit: I would think the bug was added later in
a6024562ffd7 ("udp: Add GRO functions to UDP socket")

> Signed-off-by: Richard Gobert <richardbgobert@xxxxxxxxx>

Reviewed-by: Eric Dumazet <edumazet@xxxxxxxxxx>