diff options
| author | Jesper Dangaard Brouer <brouer@redhat.com> | 2021-02-09 16:38:14 +0300 |
|---|---|---|
| committer | Daniel Borkmann <daniel@iogearbox.net> | 2021-02-13 03:14:08 +0300 |
| commit | 2c0a10af688c02adcf127aad29e923e0056c6b69 (patch) | |
| tree | ffe3309649bc3ca4aadfbc18cea554513f05ff6f /net/core | |
| parent | 6306c1189e77a513bf02720450bb43bd4ba5d8ae (diff) | |
| download | linux-2c0a10af688c02adcf127aad29e923e0056c6b69.tar.xz | |
bpf: Fix bpf_fib_lookup helper MTU check for SKB ctx
BPF end-user on Cilium slack-channel (Carlo Carraro) wants to use
bpf_fib_lookup for doing MTU-check, but *prior* to extending packet size,
by adjusting fib_params 'tot_len' with the packet length plus the expected
encap size. (Just like the bpf_check_mtu helper supports). He discovered
that for SKB ctx the param->tot_len was not used, instead skb->len was used
(via MTU check in is_skb_forwardable() that checks against netdev MTU).
Fix this by using fib_params 'tot_len' for MTU check. If not provided (e.g.
zero) then keep existing TC behaviour intact. Notice that 'tot_len' for MTU
check is done like XDP code-path, which checks against FIB-dst MTU.
V16:
- Revert V13 optimization, 2nd lookup is against egress/resulting netdev
V13:
- Only do ifindex lookup one time, calling dev_get_by_index_rcu().
V10:
- Use same method as XDP for 'tot_len' MTU check
Fixes: 4c79579b44b1 ("bpf: Change bpf_fib_lookup to return lookup status")
Reported-by: Carlo Carraro <colrack@gmail.com>
Signed-off-by: Jesper Dangaard Brouer <brouer@redhat.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Link: https://lore.kernel.org/bpf/161287789444.790810.15247494756551413508.stgit@firesoul
Diffstat (limited to 'net/core')
| -rw-r--r-- | net/core/filter.c | 13 |
1 files changed, 10 insertions, 3 deletions
diff --git a/net/core/filter.c b/net/core/filter.c index 27022168fd78..1fec2e998e37 100644 --- a/net/core/filter.c +++ b/net/core/filter.c @@ -5581,6 +5581,7 @@ BPF_CALL_4(bpf_skb_fib_lookup, struct sk_buff *, skb, { struct net *net = dev_net(skb->dev); int rc = -EAFNOSUPPORT; + bool check_mtu = false; if (plen < sizeof(*params)) return -EINVAL; @@ -5588,22 +5589,28 @@ BPF_CALL_4(bpf_skb_fib_lookup, struct sk_buff *, skb, if (flags & ~(BPF_FIB_LOOKUP_DIRECT | BPF_FIB_LOOKUP_OUTPUT)) return -EINVAL; + if (params->tot_len) + check_mtu = true; + switch (params->family) { #if IS_ENABLED(CONFIG_INET) case AF_INET: - rc = bpf_ipv4_fib_lookup(net, params, flags, false); + rc = bpf_ipv4_fib_lookup(net, params, flags, check_mtu); break; #endif #if IS_ENABLED(CONFIG_IPV6) case AF_INET6: - rc = bpf_ipv6_fib_lookup(net, params, flags, false); + rc = bpf_ipv6_fib_lookup(net, params, flags, check_mtu); break; #endif } - if (!rc) { + if (rc == BPF_FIB_LKUP_RET_SUCCESS && !check_mtu) { struct net_device *dev; + /* When tot_len isn't provided by user, check skb + * against MTU of FIB lookup resulting net_device + */ dev = dev_get_by_index_rcu(net, params->ifindex); if (!is_skb_forwardable(dev, skb)) rc = BPF_FIB_LKUP_RET_FRAG_NEEDED; |