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authorJesper Dangaard Brouer <brouer@redhat.com>2021-02-09 14:38:14 +0100
committerDaniel Borkmann <daniel@iogearbox.net>2021-02-13 01:14:08 +0100
commit2c0a10af688c02adcf127aad29e923e0056c6b69 (patch)
treeffe3309649bc3ca4aadfbc18cea554513f05ff6f /net
parent6306c1189e77a513bf02720450bb43bd4ba5d8ae (diff)
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')
-rw-r--r--net/core/filter.c13
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;