[PATCH bpf-next V15 2/7] bpf: fix bpf_fib_lookup helper MTU check for SKB ctx
From: Jesper Dangaard Brouer <hidden>
Date: 2021-02-02 16:51:30
Also in:
bpf
Subsystem:
bpf [general] (safe dynamic programs and tools), bpf [networking] (tcx & tc bpf, sock_addr), networking [general], the rest · Maintainers:
Alexei Starovoitov, Daniel Borkmann, Andrii Nakryiko, Eduard Zingerman, Kumar Kartikeya Dwivedi, Martin KaFai Lau, "David S. Miller", Eric Dumazet, Jakub Kicinski, Paolo Abeni, Linus Torvalds
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 <redacted>
Signed-off-by: Jesper Dangaard Brouer <redacted>
Acked-by: John Fastabend <john.fastabend@gmail.com>
---
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; }