netdev - Re: [PATCH v5 bpf 1/4] lwt: fix return values of BPF ops

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <CAO3-Pbo9rx_8GS2V8f4hwAzrJ00UC=g1NjCNx2ymnHWSXmUmvA@mail.gmail.com>
Date: Tue, 15 Aug 2023 22:05:11 -0500
From: Yan Zhai <yan@...udflare.com>
To: bpf@...r.kernel.org
Cc: "David S. Miller" <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>, 
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>, David Ahern <dsahern@...nel.org>, 
	Alexei Starovoitov <ast@...nel.org>, Daniel Borkmann <daniel@...earbox.net>, 
	Andrii Nakryiko <andrii@...nel.org>, Martin KaFai Lau <martin.lau@...ux.dev>, Song Liu <song@...nel.org>, 
	Yonghong Song <yhs@...com>, John Fastabend <john.fastabend@...il.com>, KP Singh <kpsingh@...nel.org>, 
	Stanislav Fomichev <sdf@...gle.com>, Hao Luo <haoluo@...gle.com>, Jiri Olsa <jolsa@...nel.org>, 
	Mykola Lysenko <mykolal@...com>, Shuah Khan <shuah@...nel.org>, Thomas Graf <tgraf@...g.ch>, 
	Jordan Griege <jgriege@...udflare.com>, Dan Carpenter <dan.carpenter@...aro.org>, 
	linux-kernel@...r.kernel.org, netdev@...r.kernel.org, 
	linux-kselftest@...r.kernel.org, stable@...r.kernel.org
Subject: Re: [PATCH v5 bpf 1/4] lwt: fix return values of BPF ops

On Tue, Aug 15, 2023 at 9:54 PM Yan Zhai <yan@...udflare.com> wrote:
>
> BPF encap ops can return different types of positive values, such like
> NET_RX_DROP, NET_XMIT_CN, NETDEV_TX_BUSY, and so on, from function
> skb_do_redirect and bpf_lwt_xmit_reroute. At the xmit hook, such return
> values would be treated implicitly as LWTUNNEL_XMIT_CONTINUE in
> ip(6)_finish_output2. When this happens, skbs that have been freed would
> continue to the neighbor subsystem, causing use-after-free bug and
> kernel crashes.
>
> To fix the incorrect behavior, skb_do_redirect return values can be
> simply discarded, the same as tc-egress behavior. On the other hand,
> bpf_lwt_xmit_reroute returns useful errors to local senders, e.g. PMTU
> information. Thus convert its return values to avoid the conflict with
> LWTUNNEL_XMIT_CONTINUE.
>
> Fixes: 3a0af8fd61f9 ("bpf: BPF for lightweight tunnel infrastructure")
> Suggested-by: Martin KaFai Lau <martin.lau@...ux.dev>
> Suggested-by: Stanislav Fomichev <sdf@...gle.com>
> Reported-by: Jordan Griege <jgriege@...udflare.com>
> Signed-off-by: Yan Zhai <yan@...udflare.com>
> ---
> * v5: discards skb_do_redirect return instead; convert
>       bpf_lwt_xmit_reroute return;
> * v4: minor commit message changes
> * v3: converts skb_do_redirect statuses from both ingress and egress
> * v2: code style amend
> ---
>  net/core/lwt_bpf.c | 7 +++----
>  1 file changed, 3 insertions(+), 4 deletions(-)
>
> diff --git a/net/core/lwt_bpf.c b/net/core/lwt_bpf.c
> index 8b6b5e72b217..4a0797f0a154 100644
> --- a/net/core/lwt_bpf.c
> +++ b/net/core/lwt_bpf.c
> @@ -60,9 +60,8 @@ static int run_lwt_bpf(struct sk_buff *skb, struct bpf_lwt_prog *lwt,
>                         ret = BPF_OK;
>                 } else {
>                         skb_reset_mac_header(skb);
> -                       ret = skb_do_redirect(skb);
> -                       if (ret == 0)
> -                               ret = BPF_REDIRECT;
> +                       skb_do_redirect(skb);
> +                       ret = BPF_REDIRECT;
>                 }
>                 break;
>
> @@ -255,7 +254,7 @@ static int bpf_lwt_xmit_reroute(struct sk_buff *skb)
>
>         err = dst_output(dev_net(skb_dst(skb)->dev), skb->sk, skb);
>         if (unlikely(err))
> -               return err;
> +               return net_xmit_errno(err);
>
>         /* ip[6]_finish_output2 understand LWTUNNEL_XMIT_DONE */
>         return LWTUNNEL_XMIT_DONE;
> --
> 2.30.2
>

no idea why this one would appear nested and without subject on the
lore link. Let me double check what goes wrong with my mutt setting :(

--
Yan