Matthew Cover wrote:
> Allow looking up an nf_conn. This allows eBPF programs to leverage
> nf_conntrack state for similar purposes to socket state use cases,
> as provided by the socket lookup helpers. This is particularly
> useful when nf_conntrack state is locally available, but socket
> state is not.
>
> Signed-off-by: Matthew Cover <matthew.cover@xxxxxxxxxxxxx>
> ---
Couple coding comments below. Also looks like a couple build errors
so fix those up. I'm still thinking over this though.
Also I prefer the tests in their own patch. So make it a two patch
series.
fwiw I think we could build a native xdp lib for connection tracking
but maybe there are reasons to pull in core conn tracking. Seems like
a separate discussion.
> + * struct bpf_nf_conn *bpf_ct_lookup_udp(void *ctx, struct bpf_nf_conntrack_tuple *tuple, u32 tuple_size, u64 netns, u64 flags)
> + * Description
> + * Look for UDP nf_conntrack entry matching *tuple*, optionally in
> + * a child network namespace *netns*. The return value must be
> + * checked, and if non-**NULL**, released via
> + * **bpf_ct_release**\ ().
> + *
> + * The *ctx* should point to the context of the program, such as
> + * the skb or xdp_md (depending on the hook in use). This is used
> + * to determine the base network namespace for the lookup.
> + *
> + * *tuple_size* must be one of:
> + *
> + * **sizeof**\ (*tuple*\ **->ipv4**)
> + * Look for an IPv4 nf_conn.
> + * **sizeof**\ (*tuple*\ **->ipv6**)
> + * Look for an IPv6 nf_conn.
> + *
> + * If the *netns* is a negative signed 32-bit integer, then the
> + * nf_conn lookup table in the netns associated with the *ctx* will
> + * will be used. For the TC hooks, this is the netns of the device
> + * in the skb. For XDP hooks, this is the netns of the device in
> + * the xdp_md. If *netns* is any other signed 32-bit value greater
> + * than or equal to zero then it specifies the ID of the netns
> + * relative to the netns associated with the *ctx*. *netns* values
> + * beyond the range of 32-bit integers are reserved for future
> + * use.
I find the usage of netns a bit awkward. Its being passed as a u64 and
then used as a signed int with the pivot depending on negative?
How about pivot on a flag instead of the signed bit of netns here.
> + *
> + * All values for *flags* are reserved for future usage, and must
> + * be left at zero.
> + *
> + * This helper is available only if the kernel was compiled with
> + * **CONFIG_NF_CONNTRACK=y** configuration option.
I suspect this should be,
"This helper will return NULL if the kernel was compiled with ..."
Same comment for the earlier _tcp helper.
> + * Return
> + * Pointer to **struct bpf_nf_conn**, or **NULL** in case of
> + * failure.
> + *
> + * int bpf_ct_release(struct bpf_nf_conn *ct)
> + * Description
> + * Release the reference held by *ct*. *ct* must be a
> + * non-**NULL** pointer that was returned from
> + * **bpf_ct_lookup_xxx**\ ().
> + * Return
> + * 0 on success, or a negative error in case of failure.
> */
> #define __BPF_FUNC_MAPPER(FN) \
> FN(unspec), \
[...]
> /* integer value in 'imm' field of BPF_CALL instruction selects which helper
> * function eBPF program intends to call
> @@ -3278,6 +3363,30 @@ struct bpf_sock_tuple {
> };
> };
>
> +struct bpf_nf_conn {
> + __u32 cpu;
> + __u32 mark;
> + __u32 status;
> + __u32 timeout;
> +};
> +
> +struct bpf_nf_conntrack_tuple {
> + union {
> + struct {
> + __be32 saddr;
> + __be32 daddr;
> + __be16 sport;
> + __be16 dport;
> + } ipv4;
> + struct {
> + __be32 saddr[4];
> + __be32 daddr[4];
> + __be16 sport;
> + __be16 dport;
> + } ipv6;
> + };
> +};
> +
[...]
> +static int check_nf_ct_access(struct bpf_verifier_env *env, int insn_idx,
> + u32 regno, int off, int size,
> + enum bpf_access_type t)
> +{
> + struct bpf_reg_state *regs = cur_regs(env);
> + struct bpf_reg_state *reg = ®s[regno];
> + struct bpf_insn_access_aux info = {};
> + bool valid;
> +
> + switch (reg->type) {
> + case PTR_TO_NF_CONN:
> + valid = bpf_nf_conn_is_valid_access(off, size, t, &info);
> + break;
> + default:
> + valid = false;
> + }
> +
> + if (valid) {
> + env->insn_aux_data[insn_idx].ctx_field_size =
> + info.ctx_field_size;
> + return 0;
> + }
> +
> + verbose(env, "R%d invalid %s access off=%d size=%d\n",
> + regno, reg_type_str[reg->type], off, size);
> +
> + return -EACCES;
nit, but this construction feels odd to me. How about,
if (reg->type != PTR_TO_NF_CONN) {
verbose(...)
return -EACCES;
}
env-> ...
return 0;
The switch sort of implies you have some ideas on future types? What would
those be?
> +}
> +
> static int check_sock_access(struct bpf_verifier_env *env, int insn_idx,
> u32 regno, int off, int size,
> enum bpf_access_type t)
> @@ -2511,6 +2556,13 @@ static bool is_ctx_reg(struct bpf_verifier_env *env, int regno)
> return reg->type == PTR_TO_CTX;
> }
[...]
> diff --git a/net/core/filter.c b/net/core/filter.c
> index 17de674..39ba965 100644
> --- a/net/core/filter.c
> +++ b/net/core/filter.c
> @@ -74,6 +74,12 @@
[...]
> +static struct nf_conn *
> +__bpf_ct_lookup(struct sk_buff *skb, struct bpf_nf_conntrack_tuple *tuple, u32 len,
> + struct net *caller_net, u8 proto, u64 netns_id, u64 flags)
Why not just make netns an int instead of pulling a unsigned from the helper and
then converting it into an int?
> +{
> + struct nf_conn *ct = NULL;
> + u8 family = AF_UNSPEC;
> + struct net *net;
> +
> + if (len == sizeof(tuple->ipv4))
> + family = AF_INET;
> + else if (len == sizeof(tuple->ipv6))
> + family = AF_INET6;
> + else
> + goto out;
> +
> + if (unlikely(family == AF_UNSPEC || flags ||
> + !((s32)netns_id < 0 || netns_id <= S32_MAX)))
^^^^^^^^^^^^^^^^^^^^
If you pass an int here and use flags to set the type I think you avoid this
check.
> + goto out;
> +
> + if ((s32)netns_id < 0) {
I don't like this casting here again fallout from u64->int conversion.
> + net = caller_net;
> + ct = ct_lookup(net, tuple, family, proto);
> + } else {
> + net = get_net_ns_by_id(caller_net, netns_id);
> + if (unlikely(!net))
> + goto out;
> + ct = ct_lookup(net, tuple, family, proto);
> + put_net(net);
> + }
> +
> +out:
> + return ct;
> +}
> +
[...]
Thanks!
John
