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Commit a70b506e authored by Daniel Borkmann's avatar Daniel Borkmann Committed by David S. Miller
Browse files

bpf: enforce recursion limit on redirects 



Respect the stack's xmit_recursion limit for calls into dev_queue_xmit().
Currently, they are not handeled by the limiter when attached to clsact's
egress parent, for example, and a buggy program redirecting it to the
same device again could run into stack overflow eventually. It would be
good if we could notify an admin to give him a chance to react. We reuse
xmit_recursion instead of having one private to eBPF, so that the stack's
current recursion depth will be taken into account as well. Follow-up to
commit 3896d655 ("bpf: introduce bpf_clone_redirect() helper") and
27b29f63 ("bpf: add bpf_redirect() helper").

Signed-off-by: default avatarDaniel Borkmann <daniel@iogearbox.net>
Acked-by: default avatarAlexei Starovoitov <ast@kernel.org>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent f2a4d086

include/linux/netdevice.h

+2 −0
Original line number Diff line number Diff line
@@ -2389,6 +2389,8 @@ void synchronize_net(void); 
int init_dummy_netdev(struct net_device *dev);



DECLARE_PER_CPU(int, xmit_recursion);

#define XMIT_RECURSION_LIMIT	10



static inline int dev_recursion_level(void)

{

	return this_cpu_read(xmit_recursion);

net/core/dev.c

+2 −4
Original line number Diff line number Diff line
@@ -3144,8 +3144,6 @@ static void skb_update_prio(struct sk_buff *skb) 
DEFINE_PER_CPU(int, xmit_recursion);

EXPORT_SYMBOL(xmit_recursion);



#define RECURSION_LIMIT 10



/**

 *	dev_loopback_xmit - loop back @skb

 *	@net: network namespace this loopback is happening in
@@ -3388,8 +3386,8 @@ static int __dev_queue_xmit(struct sk_buff *skb, void *accel_priv) 
		int cpu = smp_processor_id(); /* ok because BHs are off */



		if (txq->xmit_lock_owner != cpu) {



			if (__this_cpu_read(xmit_recursion) > RECURSION_LIMIT)

			if (unlikely(__this_cpu_read(xmit_recursion) >

				     XMIT_RECURSION_LIMIT))

				goto recursion_alert;



			skb = validate_xmit_skb(skb, dev);

net/core/filter.c

+34 −21
Original line number Diff line number Diff line
@@ -1603,9 +1603,36 @@ static const struct bpf_func_proto bpf_csum_diff_proto = { 
	.arg5_type	= ARG_ANYTHING,

};



static inline int __bpf_rx_skb(struct net_device *dev, struct sk_buff *skb)

{

	if (skb_at_tc_ingress(skb))

		skb_postpush_rcsum(skb, skb_mac_header(skb), skb->mac_len);



	return dev_forward_skb(dev, skb);

}



static inline int __bpf_tx_skb(struct net_device *dev, struct sk_buff *skb)

{

	int ret;



	if (unlikely(__this_cpu_read(xmit_recursion) > XMIT_RECURSION_LIMIT)) {

		net_crit_ratelimited("bpf: recursion limit reached on datapath, buggy bpf program?\n");

		kfree_skb(skb);

		return -ENETDOWN;

	}



	skb->dev = dev;



	__this_cpu_inc(xmit_recursion);

	ret = dev_queue_xmit(skb);

	__this_cpu_dec(xmit_recursion);



	return ret;

}



static u64 bpf_clone_redirect(u64 r1, u64 ifindex, u64 flags, u64 r4, u64 r5)

{

	struct sk_buff *skb = (struct sk_buff *) (long) r1, *skb2;

	struct sk_buff *skb = (struct sk_buff *) (long) r1;

	struct net_device *dev;



	if (unlikely(flags & ~(BPF_F_INGRESS)))
@@ -1615,19 +1642,12 @@ static u64 bpf_clone_redirect(u64 r1, u64 ifindex, u64 flags, u64 r4, u64 r5) 
	if (unlikely(!dev))

		return -EINVAL;



	skb2 = skb_clone(skb, GFP_ATOMIC);

	if (unlikely(!skb2))

	skb = skb_clone(skb, GFP_ATOMIC);

	if (unlikely(!skb))

		return -ENOMEM;



	if (flags & BPF_F_INGRESS) {

		if (skb_at_tc_ingress(skb2))

			skb_postpush_rcsum(skb2, skb_mac_header(skb2),

					   skb2->mac_len);

		return dev_forward_skb(dev, skb2);

	}



	skb2->dev = dev;

	return dev_queue_xmit(skb2);

	return flags & BPF_F_INGRESS ?

	       __bpf_rx_skb(dev, skb) : __bpf_tx_skb(dev, skb);

}



static const struct bpf_func_proto bpf_clone_redirect_proto = {
@@ -1671,15 +1691,8 @@ int skb_do_redirect(struct sk_buff *skb) 
		return -EINVAL;

	}



	if (ri->flags & BPF_F_INGRESS) {

		if (skb_at_tc_ingress(skb))

			skb_postpush_rcsum(skb, skb_mac_header(skb),

					   skb->mac_len);

		return dev_forward_skb(dev, skb);

	}



	skb->dev = dev;

	return dev_queue_xmit(skb);

	return ri->flags & BPF_F_INGRESS ?

	       __bpf_rx_skb(dev, skb) : __bpf_tx_skb(dev, skb);

}



static const struct bpf_func_proto bpf_redirect_proto = {