On Mon, Oct 21, 2019 at 10:09:47PM +0200, Matteo Croce wrote:
> The ICMP flow dissector currently parses only the Type and Code fields.
> Some ICMP packets (echo, timestamp) have a 16 bit Identifier field which
> is used to correlate packets.
> Add such field in flow_dissector_key_icmp and replace skb_flow_get_be16()
> with a more complex function which populate this field.
>
> Signed-off-by: Matteo Croce <mcr...@redhat.com>
> ---
> include/net/flow_dissector.h | 10 +++++-
> net/core/flow_dissector.c | 64 ++++++++++++++++++++++--------------
> 2 files changed, 49 insertions(+), 25 deletions(-)
>
> diff --git a/include/net/flow_dissector.h b/include/net/flow_dissector.h
> index 7747af3cc500..86c6bf5eab31 100644
> --- a/include/net/flow_dissector.h
> +++ b/include/net/flow_dissector.h
> @@ -6,6 +6,8 @@
> #include <linux/in6.h>
> #include <uapi/linux/if_ether.h>
>
> +struct sk_buff;
> +
> /**
> * struct flow_dissector_key_control:
> * @thoff: Transport header offset
> @@ -160,6 +162,7 @@ struct flow_dissector_key_ports {
> * icmp: ICMP type (high) and code (low)
> * type: ICMP type
> * code: ICMP code
> + * id: session identifier
> */
> struct flow_dissector_key_icmp {
> union {
> @@ -169,6 +172,7 @@ struct flow_dissector_key_icmp {
> u8 code;
> };
> };
> + u16 id;
> };
>
> /**
> @@ -282,6 +286,7 @@ struct flow_keys {
> struct flow_dissector_key_vlan cvlan;
> struct flow_dissector_key_keyid keyid;
> struct flow_dissector_key_ports ports;
> + struct flow_dissector_key_icmp icmp;
> /* 'addrs' must be the last member */
> struct flow_dissector_key_addrs addrs;
> };
> @@ -312,10 +317,13 @@ void make_flow_keys_digest(struct flow_keys_digest
> *digest,
>
> static inline bool flow_keys_have_l4(const struct flow_keys *keys)
> {
> - return (keys->ports.ports || keys->tags.flow_label);
> + return keys->ports.ports || keys->tags.flow_label || keys->icmp.id;
> }
>
> u32 flow_hash_from_keys(struct flow_keys *keys);
> +void skb_flow_get_icmp_tci(const struct sk_buff *skb,
> + struct flow_dissector_key_icmp *key_icmp,
> + void *data, int thoff, int hlen);
>
> static inline bool dissector_uses_key(const struct flow_dissector
> *flow_dissector,
> enum flow_dissector_key_id key_id)
> diff --git a/net/core/flow_dissector.c b/net/core/flow_dissector.c
> index 6443fac65ce8..90dcf6f2ef19 100644
> --- a/net/core/flow_dissector.c
> +++ b/net/core/flow_dissector.c
> @@ -147,27 +147,6 @@ int skb_flow_dissector_bpf_prog_detach(const union
> bpf_attr *attr)
> mutex_unlock(&flow_dissector_mutex);
> return 0;
> }
> -/**
> - * skb_flow_get_be16 - extract be16 entity
> - * @skb: sk_buff to extract from
> - * @poff: offset to extract at
> - * @data: raw buffer pointer to the packet
> - * @hlen: packet header length
> - *
> - * The function will try to retrieve a be32 entity at
> - * offset poff
> - */
> -static __be16 skb_flow_get_be16(const struct sk_buff *skb, int poff,
> - void *data, int hlen)
> -{
> - __be16 *u, _u;
> -
> - u = __skb_header_pointer(skb, poff, sizeof(_u), data, hlen, &_u);
> - if (u)
> - return *u;
> -
> - return 0;
> -}
>
> /**
> * __skb_flow_get_ports - extract the upper layer ports and return them
> @@ -203,8 +182,44 @@ __be32 __skb_flow_get_ports(const struct sk_buff *skb,
> int thoff, u8 ip_proto,
> }
> EXPORT_SYMBOL(__skb_flow_get_ports);
>
> -/* If FLOW_DISSECTOR_KEY_ICMP is set, get the Type and Code from an ICMP
> packet
> - * using skb_flow_get_be16().
> +/**
> + * skb_flow_get_icmp_tci - extract ICMP(6) Type, Code and Identifier fields
> + * @skb: sk_buff to extract from
> + * @key_icmp: struct flow_dissector_key_icmp to fill
> + * @data: raw buffer pointer to the packet
> + * @toff: offset to extract at
> + * @hlen: packet header length
> + */
> +void skb_flow_get_icmp_tci(const struct sk_buff *skb,
> + struct flow_dissector_key_icmp *key_icmp,
> + void *data, int thoff, int hlen)
> +{
> + struct icmphdr *ih, _ih;
> +
> + ih = __skb_header_pointer(skb, thoff, sizeof(_ih), data, hlen, &_ih);
> + if (!ih)
> + return;
> +
> + key_icmp->type = ih->type;
> + key_icmp->code = ih->code;
> + key_icmp->id = 0;
> + switch (ih->type) {
> + case ICMP_ECHO:
> + case ICMP_ECHOREPLY:
> + case ICMP_TIMESTAMP:
> + case ICMP_TIMESTAMPREPLY:
> + case ICMPV6_ECHO_REQUEST:
> + case ICMPV6_ECHO_REPLY:
> + /* As we use 0 to signal that the Id field is not present,
> + * avoid confusion with packets without such field
> + */
> + key_icmp->id = ih->un.echo.id ? : 1;
Its not obvious to me why the kernel should treat id-zero as a special
value if it is not special on the wire.
Perhaps a caller who needs to know if the id is present can
check the ICMP type as this code does, say using a helper.
> + }
> +}
> +EXPORT_SYMBOL(skb_flow_get_icmp_tci);
> +
> +/* If FLOW_DISSECTOR_KEY_ICMP is set, dissect an ICMP packet
> + * using skb_flow_get_icmp_tci().
> */
> static void __skb_flow_dissect_icmp(const struct sk_buff *skb,
> struct flow_dissector *flow_dissector,
> @@ -219,7 +234,8 @@ static void __skb_flow_dissect_icmp(const struct sk_buff
> *skb,
> key_icmp = skb_flow_dissector_target(flow_dissector,
> FLOW_DISSECTOR_KEY_ICMP,
> target_container);
> - key_icmp->icmp = skb_flow_get_be16(skb, thoff, data, hlen);
> +
> + skb_flow_get_icmp_tci(skb, key_icmp, data, thoff, hlen);
> }
>
> void skb_flow_dissect_meta(const struct sk_buff *skb,
> --
> 2.21.0
>
