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.
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@xxxxxxxxx>
Signed-off-by: Jesper Dangaard Brouer <brouer@xxxxxxxxxx>
Acked-by: John Fastabend <john.fastabend@xxxxxxxxx>
---
net/core/filter.c | 50 ++++++++++++++++++++++++++++----------------------
1 file changed, 28 insertions(+), 22 deletions(-)
diff --git a/net/core/filter.c b/net/core/filter.c
index 5beadd659091..252fbb294001 100644
--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -5301,22 +5301,18 @@ static int bpf_fib_set_fwd_params(struct bpf_fib_lookup *params,
#endif
#if IS_ENABLED(CONFIG_INET)
-static int bpf_ipv4_fib_lookup(struct net *net, struct bpf_fib_lookup *params,
+static int bpf_ipv4_fib_lookup(struct net *net, struct net_device *dev,
+ struct bpf_fib_lookup *params,
u32 flags, bool check_mtu)
{
struct fib_nh_common *nhc;
struct in_device *in_dev;
struct neighbour *neigh;
- struct net_device *dev;
struct fib_result res;
struct flowi4 fl4;
int err;
u32 mtu;
- dev = dev_get_by_index_rcu(net, params->ifindex);
- if (unlikely(!dev))
- return -ENODEV;
-
/* verify forwarding is enabled on this interface */
in_dev = __in_dev_get_rcu(dev);
if (unlikely(!in_dev || !IN_DEV_FORWARD(in_dev)))
@@ -5418,14 +5414,14 @@ static int bpf_ipv4_fib_lookup(struct net *net, struct bpf_fib_lookup *params,
#endif
#if IS_ENABLED(CONFIG_IPV6)
-static int bpf_ipv6_fib_lookup(struct net *net, struct bpf_fib_lookup *params,
+static int bpf_ipv6_fib_lookup(struct net *net, struct net_device *dev,
+ struct bpf_fib_lookup *params,
u32 flags, bool check_mtu)
{
struct in6_addr *src = (struct in6_addr *) params->ipv6_src;
struct in6_addr *dst = (struct in6_addr *) params->ipv6_dst;
struct fib6_result res = {};
struct neighbour *neigh;
- struct net_device *dev;
struct inet6_dev *idev;
struct flowi6 fl6;
int strict = 0;
@@ -5436,10 +5432,6 @@ static int bpf_ipv6_fib_lookup(struct net *net, struct bpf_fib_lookup *params,
if (rt6_need_strict(dst) || rt6_need_strict(src))
return BPF_FIB_LKUP_RET_NOT_FWDED;
- dev = dev_get_by_index_rcu(net, params->ifindex);
- if (unlikely(!dev))
- return -ENODEV;
-
idev = __in6_dev_get_safely(dev);
if (unlikely(!idev || !idev->cnf.forwarding))
return BPF_FIB_LKUP_RET_FWD_DISABLED;
@@ -5533,22 +5525,27 @@ static int bpf_ipv6_fib_lookup(struct net *net, struct bpf_fib_lookup *params,
BPF_CALL_4(bpf_xdp_fib_lookup, struct xdp_buff *, ctx,
struct bpf_fib_lookup *, params, int, plen, u32, flags)
{
+ struct net *net = dev_net(ctx->rxq->dev);
+ struct net_device *dev;
+
if (plen < sizeof(*params))
return -EINVAL;
if (flags & ~(BPF_FIB_LOOKUP_DIRECT | BPF_FIB_LOOKUP_OUTPUT))
return -EINVAL;
+ dev = dev_get_by_index_rcu(net, params->ifindex);
+ if (unlikely(!dev))
+ return -ENODEV;
+
switch (params->family) {
#if IS_ENABLED(CONFIG_INET)
case AF_INET:
- return bpf_ipv4_fib_lookup(dev_net(ctx->rxq->dev), params,
- flags, true);
+ return bpf_ipv4_fib_lookup(net, dev, params, flags, true);
#endif
#if IS_ENABLED(CONFIG_IPV6)
case AF_INET6:
- return bpf_ipv6_fib_lookup(dev_net(ctx->rxq->dev), params,
- flags, true);
+ return bpf_ipv6_fib_lookup(net, dev, params, flags, true);
#endif
}
return -EAFNOSUPPORT;
@@ -5568,7 +5565,9 @@ BPF_CALL_4(bpf_skb_fib_lookup, struct sk_buff *, skb,
struct bpf_fib_lookup *, params, int, plen, u32, flags)
{
struct net *net = dev_net(skb->dev);
+ struct net_device *dev;
int rc = -EAFNOSUPPORT;
+ bool check_mtu = false;
if (plen < sizeof(*params))
return -EINVAL;
@@ -5576,23 +5575,30 @@ BPF_CALL_4(bpf_skb_fib_lookup, struct sk_buff *, skb,
if (flags & ~(BPF_FIB_LOOKUP_DIRECT | BPF_FIB_LOOKUP_OUTPUT))
return -EINVAL;
+ dev = dev_get_by_index_rcu(net, params->ifindex);
+ if (unlikely(!dev))
+ return -ENODEV;
+
+ 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, dev, 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, dev, params, flags, check_mtu);
break;
#endif
}
- if (!rc) {
- struct net_device *dev;
-
- dev = dev_get_by_index_rcu(net, params->ifindex);
+ if (rc == BPF_FIB_LKUP_RET_SUCCESS && !check_mtu) {
+ /* When tot_len isn't provided by user,
+ * check skb against net_device MTU
+ */
if (!is_skb_forwardable(dev, skb))
rc = BPF_FIB_LKUP_RET_FRAG_NEEDED;
}
