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bpf: Support getting tunnel flags

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Existing 'bpf_skb_get_tunnel_key' extracts various tunnel parameters
(id, ttl, tos, local and remote) but does not expose ip_tunnel_info's
tun_flags to the BPF program.

It makes sense to expose tun_flags to the BPF program.

Assume for example multiple GRE tunnels maintained on a single GRE
interface in collect_md mode. The program expects origins to initiate
over GRE, however different origins use different GRE characteristics
(e.g. some prefer to use GRE checksum, some do not; some pass a GRE key,
some do not, etc..).

A BPF program getting tun_flags can therefore remember the relevant
flags (e.g. TUNNEL_CSUM, TUNNEL_SEQ...) for each initiating remote. In
the reply path, the program can use 'bpf_skb_set_tunnel_key' in order
to correctly reply to the remote, using similar characteristics, based
on the stored tunnel flags.

Introduce BPF_F_TUNINFO_FLAGS flag for bpf_skb_get_tunnel_key. If
specified, 'bpf_tunnel_key->tunnel_flags' is set with the tun_flags.

Decided to use the existing unused 'tunnel_ext' as the storage for the
'tunnel_flags' in order to avoid changing bpf_tunnel_key's layout.

Also, the following has been considered during the design:

  1. Convert the "interesting" internal TUNNEL_xxx flags back to BPF_F_yyy
     and place into the new 'tunnel_flags' field. This has 2 drawbacks:

     - The BPF_F_yyy flags are from *set_tunnel_key* enumeration space,
       e.g. BPF_F_ZERO_CSUM_TX. It is awkward that it is "returned" into
       tunnel_flags from a *get_tunnel_key* call.
     - Not all "interesting" TUNNEL_xxx flags can be mapped to existing
       BPF_F_yyy flags, and it doesn't make sense to create new BPF_F_yyy
       flags just for purposes of the returned tunnel_flags.

  2. Place key.tun_flags into 'tunnel_flags' but mask them, keeping only
     "interesting" flags. That's ok, but the drawback is that what's
     "interesting" for my usecase might be limiting for other usecases.

Therefore I decided to expose what's in key.tun_flags *as is*, which seems
most flexible. The BPF user can just choose to ignore bits he's not
interested in. The TUNNEL_xxx are also UAPI, so no harm exposing them
back in the get_tunnel_key call.

Signed-off-by: Shmulik Ladkani <shmulik.ladkani@gmail.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Link: https://lore.kernel.org/bpf/20220831144010.174110-1-shmulik.ladkani@gmail.com
This commit is contained in:
Shmulik Ladkani 2022-08-31 17:40:09 +03:00 committed by Daniel Borkmann
parent dc84dbbcc9
commit 44c51472be
3 changed files with 24 additions and 4 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

10
include/uapi/linux/bpf.h
View file

@ -5659,6 +5659,11 @@ enum {
BPF_F_SEQ_NUMBER = (1ULL << 3),
};
/* BPF_FUNC_skb_get_tunnel_key flags. */
enum {
BPF_F_TUNINFO_FLAGS = (1ULL << 4),
};
/* BPF_FUNC_perf_event_output, BPF_FUNC_perf_event_read and
* BPF_FUNC_perf_event_read_value flags.
*/
@ -5848,7 +5853,10 @@ struct bpf_tunnel_key {
};
__u8 tunnel_tos;
__u8 tunnel_ttl;
__u16 tunnel_ext; /* Padding, future use. */
union {
__u16 tunnel_ext; /* compat */
__be16 tunnel_flags;
};
__u32 tunnel_label;
union {
__u32 local_ipv4;

8
net/core/filter.c
View file

@ -4488,7 +4488,8 @@ BPF_CALL_4(bpf_skb_get_tunnel_key, struct sk_buff *, skb, struct bpf_tunnel_key
void *to_orig = to;
int err;
if (unlikely(!info || (flags & ~(BPF_F_TUNINFO_IPV6)))) {
if (unlikely(!info || (flags & ~(BPF_F_TUNINFO_IPV6 |
BPF_F_TUNINFO_FLAGS)))) {
err = -EINVAL;
goto err_clear;
}
@ -4520,7 +4521,10 @@ BPF_CALL_4(bpf_skb_get_tunnel_key, struct sk_buff *, skb, struct bpf_tunnel_key
to->tunnel_id = be64_to_cpu(info->key.tun_id);
to->tunnel_tos = info->key.tos;
to->tunnel_ttl = info->key.ttl;
to->tunnel_ext = 0;
if (flags & BPF_F_TUNINFO_FLAGS)
to->tunnel_flags = info->key.tun_flags;
else
to->tunnel_ext = 0;
if (flags & BPF_F_TUNINFO_IPV6) {
memcpy(to->remote_ipv6, &info->key.u.ipv6.src,

10
tools/include/uapi/linux/bpf.h
View file

@ -5659,6 +5659,11 @@ enum {
BPF_F_SEQ_NUMBER = (1ULL << 3),
};
/* BPF_FUNC_skb_get_tunnel_key flags. */
enum {
BPF_F_TUNINFO_FLAGS = (1ULL << 4),
};
/* BPF_FUNC_perf_event_output, BPF_FUNC_perf_event_read and
* BPF_FUNC_perf_event_read_value flags.
*/
@ -5848,7 +5853,10 @@ struct bpf_tunnel_key {
};
__u8 tunnel_tos;
__u8 tunnel_ttl;
__u16 tunnel_ext; /* Padding, future use. */
union {
__u16 tunnel_ext; /* compat */
__be16 tunnel_flags;
};
__u32 tunnel_label;
union {
__u32 local_ipv4;