netdev - Re: [PATCH v1] bpf: Prevent infinite loops with bpf_redirect

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Message-ID: <cb613257-75c5-4bcf-9daa-c3f5d9a83186@iogearbox.net>
Date: Mon, 30 Sep 2024 09:36:38 +0200
From: Daniel Borkmann <daniel@...earbox.net>
To: Jordan Rife <jrife@...gle.com>, bpf@...r.kernel.org
Cc: netdev@...r.kernel.org, Alexei Starovoitov <ast@...nel.org>,
 Andrii Nakryiko <andrii@...nel.org>, Martin KaFai Lau
 <martin.lau@...ux.dev>, Kui-Feng Lee <thinker.li@...il.com>,
 Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>,
 "David S. Miller" <davem@...emloft.net>, Paolo Abeni <pabeni@...hat.com>,
 stable@...r.kernel.org, John Fastabend <john.fastabend@...il.com>
Subject: Re: [PATCH v1] bpf: Prevent infinite loops with bpf_redirect_peer

On 9/29/24 7:02 PM, Jordan Rife wrote:
> It is possible to create cycles using bpf_redirect_peer which lead to an
> an infinite loop inside __netif_receive_skb_core. The simplest way to
> illustrate this is by attaching a TC program to the ingress hook on both
> sides of a veth or netkit device pair which redirects to its own peer,
> although other cycles are possible. This patch places an upper limit on
> the number of iterations allowed inside __netif_receive_skb_core to
> prevent this.
>
> Signed-off-by: Jordan Rife <jrife@...gle.com>
> Fixes: 9aa1206e8f48 ("bpf: Add redirect_peer helper")
> Cc: stable@...r.kernel.org
> ---
>   net/core/dev.c                                | 11 +++-
>   net/core/dev.h                                |  1 +
>   .../selftests/bpf/prog_tests/tc_redirect.c    | 51 +++++++++++++++++++
>   .../selftests/bpf/progs/test_tc_peer.c        | 13 +++++
>   4 files changed, 75 insertions(+), 1 deletion(-)
>
> diff --git a/net/core/dev.c b/net/core/dev.c
> index cd479f5f22f6..753f8d27f47c 100644
> --- a/net/core/dev.c
> +++ b/net/core/dev.c
> @@ -5455,6 +5455,7 @@ static int __netif_receive_skb_core(struct sk_buff **pskb, bool pfmemalloc,
>   	struct net_device *orig_dev;
>   	bool deliver_exact = false;
>   	int ret = NET_RX_DROP;
> +	int loops = 0;
>   	__be16 type;
>   
>   	net_timestamp_check(!READ_ONCE(net_hotdata.tstamp_prequeue), skb);
> @@ -5521,8 +5522,16 @@ static int __netif_receive_skb_core(struct sk_buff **pskb, bool pfmemalloc,
>   		nf_skip_egress(skb, true);
>   		skb = sch_handle_ingress(skb, &pt_prev, &ret, orig_dev,
>   					 &another);
> -		if (another)
> +		if (another) {
> +			loops++;
No, as you mentioned, there are plenty of other misconfiguration 
possibilities in and
outside bpf where something can loop in the stack (or where you can lock 
yourself
out e.g. drop-all).