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bpf: bpf_fib_lookup return MTU value as output when looked up 

The BPF-helpers for FIB lookup (bpf_xdp_fib_lookup and bpf_skb_fib_lookup)
can perform MTU check and return BPF_FIB_LKUP_RET_FRAG_NEEDED. The BPF-prog
don't know the MTU value that caused this rejection.

If the BPF-prog wants to implement PMTU (Path MTU Discovery) (rfc1191) it
need to know this MTU value for the ICMP packet.

Patch change lookup and result struct bpf_fib_lookup, to contain this MTU
value as output via a union with 'tot_len' as this is the value used for
the MTU lookup.

V5:
 - Fixed uninit value spotted by Dan Carpenter.
 - Name struct output member mtu_result

Reported-by: kernel test robot <lkp@intel.com>
Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Jesper Dangaard Brouer <brouer@redhat.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: John Fastabend <john.fastabend@gmail.com>
Link: https://lore.kernel.org/bpf/161287789952.790810.13134700381067698781.stgit@firesoul
This commit is contained in:
Jesper Dangaard Brouer 2021-02-09 14:38:19 +01:00 committed by Daniel Borkmann
parent 2c0a10af68
commit e1850ea9bd
3 changed files with 33 additions and 11 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

11
include/uapi/linux/bpf.h
View File

@ -2239,6 +2239,9 @@ union bpf_attr {
* * > 0 one of **BPF_FIB_LKUP_RET_** codes explaining why the
* packet is not forwarded or needs assist from full stack
*
* If lookup fails with BPF_FIB_LKUP_RET_FRAG_NEEDED, then the MTU
* was exceeded and output params->mtu_result contains the MTU.
*
* long bpf_sock_hash_update(struct bpf_sock_ops *skops, struct bpf_map *map, void *key, u64 flags)
* Description
* Add an entry to, or update a sockhash *map* referencing sockets.
@ -4990,9 +4993,13 @@ struct bpf_fib_lookup {
__be16 sport;
__be16 dport;
/* total length of packet from network header - used for MTU check */
__u16 tot_len;
union { /* used for MTU check */
/* input to lookup */
__u16 tot_len; /* L3 length from network hdr (iph->tot_len) */
/* output: MTU value */
__u16 mtu_result;
};
/* input: L3 device index for lookup
* output: device index from FIB lookup
*/

22
net/core/filter.c
View File

@ -5301,12 +5301,14 @@ static const struct bpf_func_proto bpf_skb_get_xfrm_state_proto = {
#if IS_ENABLED(CONFIG_INET) || IS_ENABLED(CONFIG_IPV6)
static int bpf_fib_set_fwd_params(struct bpf_fib_lookup *params,
const struct neighbour *neigh,
const struct net_device *dev)
const struct net_device *dev, u32 mtu)
{
memcpy(params->dmac, neigh->ha, ETH_ALEN);
memcpy(params->smac, dev->dev_addr, ETH_ALEN);
params->h_vlan_TCI = 0;
params->h_vlan_proto = 0;
if (mtu)
params->mtu_result = mtu; /* union with tot_len */
return 0;
}
@ -5322,8 +5324,8 @@ static int bpf_ipv4_fib_lookup(struct net *net, struct bpf_fib_lookup *params,
struct net_device *dev;
struct fib_result res;
struct flowi4 fl4;
u32 mtu = 0;
int err;
u32 mtu;
dev = dev_get_by_index_rcu(net, params->ifindex);
if (unlikely(!dev))
@ -5390,8 +5392,10 @@ static int bpf_ipv4_fib_lookup(struct net *net, struct bpf_fib_lookup *params,
if (check_mtu) {
mtu = ip_mtu_from_fib_result(&res, params->ipv4_dst);
if (params->tot_len > mtu)
if (params->tot_len > mtu) {
params->mtu_result = mtu; /* union with tot_len */
return BPF_FIB_LKUP_RET_FRAG_NEEDED;
}
}
nhc = res.nhc;
@ -5425,7 +5429,7 @@ static int bpf_ipv4_fib_lookup(struct net *net, struct bpf_fib_lookup *params,
if (!neigh)
return BPF_FIB_LKUP_RET_NO_NEIGH;
return bpf_fib_set_fwd_params(params, neigh, dev);
return bpf_fib_set_fwd_params(params, neigh, dev, mtu);
}
#endif
@ -5442,7 +5446,7 @@ static int bpf_ipv6_fib_lookup(struct net *net, struct bpf_fib_lookup *params,
struct flowi6 fl6;
int strict = 0;
int oif, err;
u32 mtu;
u32 mtu = 0;
/* link local addresses are never forwarded */
if (rt6_need_strict(dst) || rt6_need_strict(src))
@ -5517,8 +5521,10 @@ static int bpf_ipv6_fib_lookup(struct net *net, struct bpf_fib_lookup *params,
if (check_mtu) {
mtu = ipv6_stub->ip6_mtu_from_fib6(&res, dst, src);
if (params->tot_len > mtu)
if (params->tot_len > mtu) {
params->mtu_result = mtu; /* union with tot_len */
return BPF_FIB_LKUP_RET_FRAG_NEEDED;
}
}
if (res.nh->fib_nh_lws)
@ -5538,7 +5544,7 @@ static int bpf_ipv6_fib_lookup(struct net *net, struct bpf_fib_lookup *params,
if (!neigh)
return BPF_FIB_LKUP_RET_NO_NEIGH;
return bpf_fib_set_fwd_params(params, neigh, dev);
return bpf_fib_set_fwd_params(params, neigh, dev, mtu);
}
#endif
@ -5614,6 +5620,8 @@ BPF_CALL_4(bpf_skb_fib_lookup, struct sk_buff *, skb,
dev = dev_get_by_index_rcu(net, params->ifindex);
if (!is_skb_forwardable(dev, skb))
rc = BPF_FIB_LKUP_RET_FRAG_NEEDED;
params->mtu_result = dev->mtu; /* union with tot_len */
}
return rc;

11
tools/include/uapi/linux/bpf.h
View File

@ -2239,6 +2239,9 @@ union bpf_attr {
* * > 0 one of **BPF_FIB_LKUP_RET_** codes explaining why the
* packet is not forwarded or needs assist from full stack
*
* If lookup fails with BPF_FIB_LKUP_RET_FRAG_NEEDED, then the MTU
* was exceeded and output params->mtu_result contains the MTU.
*
* long bpf_sock_hash_update(struct bpf_sock_ops *skops, struct bpf_map *map, void *key, u64 flags)
* Description
* Add an entry to, or update a sockhash *map* referencing sockets.
@ -4990,9 +4993,13 @@ struct bpf_fib_lookup {
__be16 sport;
__be16 dport;
/* total length of packet from network header - used for MTU check */
__u16 tot_len;
union { /* used for MTU check */
/* input to lookup */
__u16 tot_len; /* L3 length from network hdr (iph->tot_len) */
/* output: MTU value */
__u16 mtu_result;
};
/* input: L3 device index for lookup
* output: device index from FIB lookup
*/