Re: [PATCH net v3 1/2] net: gro: fix udp bad offset in socket lookup by adding {inner_}network_offset to napi_gro_cb
From: Richard Gobert
Date: Thu Apr 25 2024 - 08:00:25 EST
Willem de Bruijn wrote:
> 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@xxxxxxxxx>
>> ---
>> include/net/gro.h | 18 ++++++++++++++++--
>> net/8021q/vlan_core.c | 2 ++
>> net/core/gro.c | 1 +
>> net/ipv4/af_inet.c | 5 +----
>> net/ipv4/tcp_offload.c | 3 ++-
>> net/ipv4/udp.c | 3 ++-
>> net/ipv4/udp_offload.c | 3 ++-
>> net/ipv6/ip6_offload.c | 6 +++---
>> net/ipv6/tcpv6_offload.c | 3 ++-
>> net/ipv6/udp.c | 3 ++-
>> net/ipv6/udp_offload.c | 3 ++-
>> 11 files changed, 35 insertions(+), 15 deletions(-)
>>
>> diff --git a/include/net/gro.h b/include/net/gro.h
>> index 50f1e403dbbb..1faff23b66e8 100644
>> --- a/include/net/gro.h
>> +++ b/include/net/gro.h
>> @@ -87,6 +87,15 @@ struct napi_gro_cb {
>>
>> /* used to support CHECKSUM_COMPLETE for tunneling protocols */
>> __wsum csum;
>> +
>> + /* L3 offsets */
>> + union {
>> + struct {
>> + u16 network_offset;
>> + u16 inner_network_offset;
>> + };
>> + u16 network_offsets[2];
>> + };
>> };
>>
>> #define NAPI_GRO_CB(skb) ((struct napi_gro_cb *)(skb)->cb)
>> @@ -172,12 +181,17 @@ static inline void *skb_gro_header(struct sk_buff *skb, unsigned int hlen,
>> return ptr;
>> }
>>
>> +static inline int skb_gro_network_offset(const struct sk_buff *skb)
>> +{
>> + return NAPI_GRO_CB(skb)->network_offsets[NAPI_GRO_CB(skb)->encap_mark];
>> +}
>> +
>> static inline void *skb_gro_network_header(const struct sk_buff *skb)
>> {
>> if (skb_gro_may_pull(skb, skb_gro_offset(skb)))
>> - return skb_gro_header_fast(skb, skb_network_offset(skb));
>> + return skb_gro_header_fast(skb, skb_gro_network_offset(skb));
>>
>> - return skb_network_header(skb);
>> + return skb->data + skb_gro_network_offset(skb);
>> }
>>
>> static inline __wsum inet_gro_compute_pseudo(const struct sk_buff *skb,
>> diff --git a/net/8021q/vlan_core.c b/net/8021q/vlan_core.c
>> index f00158234505..9404dd551dfd 100644
>> --- a/net/8021q/vlan_core.c
>> +++ b/net/8021q/vlan_core.c
>> @@ -478,6 +478,8 @@ static struct sk_buff *vlan_gro_receive(struct list_head *head,
>> if (unlikely(!vhdr))
>> goto out;
>>
>> + NAPI_GRO_CB(skb)->network_offsets[NAPI_GRO_CB(skb)->encap_mark] = hlen;
>> +
>> type = vhdr->h_vlan_encapsulated_proto;
>>
>> ptype = gro_find_receive_by_type(type);
>> diff --git a/net/core/gro.c b/net/core/gro.c
>> index 83f35d99a682..c7901253a1a8 100644
>> --- a/net/core/gro.c
>> +++ b/net/core/gro.c
>> @@ -371,6 +371,7 @@ static inline void skb_gro_reset_offset(struct sk_buff *skb, u32 nhoff)
>> const skb_frag_t *frag0;
>> unsigned int headlen;
>>
>> + NAPI_GRO_CB(skb)->network_offset = 0;
>> NAPI_GRO_CB(skb)->data_offset = 0;
>> headlen = skb_headlen(skb);
>> NAPI_GRO_CB(skb)->frag0 = skb->data;
>> diff --git a/net/ipv4/af_inet.c b/net/ipv4/af_inet.c
>> index 55bd72997b31..2daf635ab99e 100644
>> --- a/net/ipv4/af_inet.c
>> +++ b/net/ipv4/af_inet.c
>> @@ -1568,10 +1568,7 @@ struct sk_buff *inet_gro_receive(struct list_head *head, struct sk_buff *skb)
>>
>> NAPI_GRO_CB(skb)->is_atomic = !!(iph->frag_off & htons(IP_DF));
>> NAPI_GRO_CB(skb)->flush |= flush;
>> - skb_set_network_header(skb, off);
>> - /* The above will be needed by the transport layer if there is one
>> - * immediately following this IP hdr.
>> - */
>> + NAPI_GRO_CB(skb)->inner_network_offset = off;
>>
>> /* Note : No need to call skb_gro_postpull_rcsum() here,
>> * as we already checked checksum over ipv4 header was 0
>> diff --git a/net/ipv4/tcp_offload.c b/net/ipv4/tcp_offload.c
>> index ebe4722bb020..be8ddf6da88c 100644
>> --- a/net/ipv4/tcp_offload.c
>> +++ b/net/ipv4/tcp_offload.c
>> @@ -332,7 +332,8 @@ struct sk_buff *tcp4_gro_receive(struct list_head *head, struct sk_buff *skb)
>>
>> INDIRECT_CALLABLE_SCOPE int tcp4_gro_complete(struct sk_buff *skb, int thoff)
>> {
>> - const struct iphdr *iph = ip_hdr(skb);
>> + const u16 offset = NAPI_GRO_CB(skb)->network_offsets[skb->encapsulation];
>> + const struct iphdr *iph = (struct iphdr *)(skb->data + offset);
>> struct tcphdr *th = tcp_hdr(skb);
>>
>> th->check = ~tcp_v4_check(skb->len - thoff, iph->saddr,
>> diff --git a/net/ipv4/udp.c b/net/ipv4/udp.c
>> index c02bf011d4a6..1399fce82b3f 100644
>> --- a/net/ipv4/udp.c
>> +++ b/net/ipv4/udp.c
>> @@ -532,7 +532,8 @@ static inline struct sock *__udp4_lib_lookup_skb(struct sk_buff *skb,
>> struct sock *udp4_lib_lookup_skb(const struct sk_buff *skb,
>> __be16 sport, __be16 dport)
>> {
>> - const struct iphdr *iph = ip_hdr(skb);
>> + const u16 offset = NAPI_GRO_CB(skb)->network_offsets[skb->encapsulation];
>> + const struct iphdr *iph = (struct iphdr *)(skb->data + offset);
>> struct net *net = dev_net(skb->dev);
>> int iif, sdif;
>>
>> diff --git a/net/ipv4/udp_offload.c b/net/ipv4/udp_offload.c
>> index 3498dd1d0694..fd29d21d579c 100644
>> --- a/net/ipv4/udp_offload.c
>> +++ b/net/ipv4/udp_offload.c
>> @@ -718,7 +718,8 @@ EXPORT_SYMBOL(udp_gro_complete);
>>
>> INDIRECT_CALLABLE_SCOPE int udp4_gro_complete(struct sk_buff *skb, int nhoff)
>> {
>> - const struct iphdr *iph = ip_hdr(skb);
>> + const u16 offset = NAPI_GRO_CB(skb)->network_offsets[skb->encapsulation];
>> + const struct iphdr *iph = (struct iphdr *)(skb->data + offset);
>> struct udphdr *uh = (struct udphdr *)(skb->data + nhoff);
>>
>> /* do fraglist only if there is no outer UDP encap (or we already processed it) */
>> diff --git a/net/ipv6/ip6_offload.c b/net/ipv6/ip6_offload.c
>> index b41e35af69ea..5d6b875a4638 100644
>> --- a/net/ipv6/ip6_offload.c
>> +++ b/net/ipv6/ip6_offload.c
>> @@ -67,7 +67,7 @@ static int ipv6_gro_pull_exthdrs(struct sk_buff *skb, int off, int proto)
>> off += len;
>> }
>>
>> - skb_gro_pull(skb, off - skb_network_offset(skb));
>> + skb_gro_pull(skb, off - skb_gro_network_offset(skb));
>> return proto;
>> }
>>
>> @@ -236,7 +236,7 @@ INDIRECT_CALLABLE_SCOPE struct sk_buff *ipv6_gro_receive(struct list_head *head,
>> if (unlikely(!iph))
>> goto out;
>>
>> - skb_set_network_header(skb, off);
>> + NAPI_GRO_CB(skb)->inner_network_offset = off;
>>
>> flush += ntohs(iph->payload_len) != skb->len - hlen;
>>
>> @@ -259,7 +259,7 @@ INDIRECT_CALLABLE_SCOPE struct sk_buff *ipv6_gro_receive(struct list_head *head,
>> NAPI_GRO_CB(skb)->proto = proto;
>>
>> flush--;
>> - nlen = skb_network_header_len(skb);
>> + nlen = skb_gro_offset(skb) - off;
>>
>> list_for_each_entry(p, head, list) {
>> const struct ipv6hdr *iph2;
>> diff --git a/net/ipv6/tcpv6_offload.c b/net/ipv6/tcpv6_offload.c
>> index 4b07d1e6c952..e70d60e0f86f 100644
>> --- a/net/ipv6/tcpv6_offload.c
>> +++ b/net/ipv6/tcpv6_offload.c
>> @@ -29,7 +29,8 @@ struct sk_buff *tcp6_gro_receive(struct list_head *head, struct sk_buff *skb)
>>
>> INDIRECT_CALLABLE_SCOPE int tcp6_gro_complete(struct sk_buff *skb, int thoff)
>> {
>> - const struct ipv6hdr *iph = ipv6_hdr(skb);
>> + const u16 offset = NAPI_GRO_CB(skb)->network_offsets[skb->encapsulation];
>> + const struct ipv6hdr *iph = (struct ipv6hdr *)(skb->data + offset);
>> struct tcphdr *th = tcp_hdr(skb);
>>
>
> Only udp code is affected, as only that can be used as tunnel.
>
> For bug fixes, let's try to avoid touching other code. Also that vlan.
>
> As a minimal patch all that is needed is the following, right?
>
> - add the fields
> - store in inet_gro_receive + ipv6_gro_receive
> - read in udp[46]_gro_complete and udp[46]_lib_lookup_skb
>
This approach is smaller, thanks for writing it down.
What do you think about doing this and still writing to
inner_network_offset exclusively in {inet,ipv6}_gro_receive? I still
prefer it for reasons discussed in the previous series. The code line
in vlan_gro_receive will still be there, but that will be the only
addition to your snippet.