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Date:   Wed, 13 Feb 2019 16:41:54 -0500
From:   Paul Moore <paul@...l-moore.com>
To:     Nazarov Sergey <s-nazarov@...dex.ru>
Cc:     "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "linux-security-module@...r.kernel.org" 
        <linux-security-module@...r.kernel.org>, davem@...emloft.net,
        kuznet@....inr.ac.ru, yoshfuji@...ux-ipv6.org
Subject: Re: [PATCH] NETWORKING: avoid use IPCB in cipso_v4_error

On Tue, Feb 12, 2019 at 10:10 AM Nazarov Sergey <s-nazarov@...dex.ru> wrote:
> Since cipso_v4_error might be called from different network stack layers, we can't safely use icmp_send there.
> icmp_send copies IP options with ip_option_echo, which uses IPCB to take access to IP header compiled data.
> But after commit 971f10ec ("tcp: better TCP_SKB_CB layout to reduce cache line misses"), IPCB can't be used
> above IP layer.
> This patch fixes the problem by creating in cipso_v4_error a local copy of compiled IP options and using it with
> introduced __icmp_send function. This looks some overloaded, but in quite rare error conditions only.
>
> The original discussion is here:
> https://lore.kernel.org/linux-security-module/16659801547571984@sas1-890ba5c2334a.qloud-c.yandex.net/
>
> Signed-off-by: Sergey Nazarov <s-nazarov@...dex.ru>
> ---
>  include/net/icmp.h    |    9 ++++++++-
>  net/ipv4/cipso_ipv4.c |   18 ++++++++++++++++--
>  net/ipv4/icmp.c       |    7 ++++---
>  3 files changed, 28 insertions(+), 6 deletions(-)

Hi Sergey,

Thanks for your work on finding this and putting a fix together.  As
we discussed previously, I think this looks good, but can you describe
the testing you did to verify that this works correctly?

> diff --git a/include/net/icmp.h b/include/net/icmp.h
> index 6ac3a5b..e0f709d 100644
> --- a/include/net/icmp.h
> +++ b/include/net/icmp.h
> @@ -22,6 +22,7 @@
>
>  #include <net/inet_sock.h>
>  #include <net/snmp.h>
> +#include <net/ip.h>
>
>  struct icmp_err {
>    int          errno;
> @@ -39,7 +40,13 @@ struct icmp_err {
>  struct sk_buff;
>  struct net;
>
> -void icmp_send(struct sk_buff *skb_in, int type, int code, __be32 info);
> +void __icmp_send(struct sk_buff *skb_in, int type, int code, __be32 info,
> +                const struct ip_options *opt);
> +static inline void icmp_send(struct sk_buff *skb_in, int type, int code, __be32 info)
> +{
> +       __icmp_send(skb_in, type, code, info, &IPCB(skb_in)->opt);
> +}
> +
>  int icmp_rcv(struct sk_buff *skb);
>  int icmp_err(struct sk_buff *skb, u32 info);
>  int icmp_init(void);
> diff --git a/net/ipv4/cipso_ipv4.c b/net/ipv4/cipso_ipv4.c
> index 777fa3b..234d12e 100644
> --- a/net/ipv4/cipso_ipv4.c
> +++ b/net/ipv4/cipso_ipv4.c
> @@ -1735,13 +1735,27 @@ int cipso_v4_validate(const struct sk_buff *skb, unsigned char **option)
>   */
>  void cipso_v4_error(struct sk_buff *skb, int error, u32 gateway)
>  {
> +       unsigned char optbuf[sizeof(struct ip_options) + 40];
> +       struct ip_options *opt = (struct ip_options *)optbuf;
> +
>         if (ip_hdr(skb)->protocol == IPPROTO_ICMP || error != -EACCES)
>                 return;
>
> +       /*
> +        * We might be called above the IP layer,
> +        * so we can not use icmp_send and IPCB here.
> +        */
> +
> +       memset(opt, 0, sizeof(struct ip_options));
> +       opt->optlen = ip_hdr(skb)->ihl*4 - sizeof(struct iphdr);
> +       memcpy(opt->__data, (unsigned char *)&(ip_hdr(skb)[1]), opt->optlen);
> +       if (ip_options_compile(dev_net(skb->dev), opt, NULL))
> +               return;
> +
>         if (gateway)
> -               icmp_send(skb, ICMP_DEST_UNREACH, ICMP_NET_ANO, 0);
> +               __icmp_send(skb, ICMP_DEST_UNREACH, ICMP_NET_ANO, 0, opt);
>         else
> -               icmp_send(skb, ICMP_DEST_UNREACH, ICMP_HOST_ANO, 0);
> +               __icmp_send(skb, ICMP_DEST_UNREACH, ICMP_HOST_ANO, 0, opt);
>  }
>
>  /**
> diff --git a/net/ipv4/icmp.c b/net/ipv4/icmp.c
> index 065997f..3f24414 100644
> --- a/net/ipv4/icmp.c
> +++ b/net/ipv4/icmp.c
> @@ -570,7 +570,8 @@ static void icmp_reply(struct icmp_bxm *icmp_param, struct sk_buff *skb)
>   *                     MUST reply to only the first fragment.
>   */
>
> -void icmp_send(struct sk_buff *skb_in, int type, int code, __be32 info)
> +void __icmp_send(struct sk_buff *skb_in, int type, int code, __be32 info,
> +                const struct ip_options *opt)
>  {
>         struct iphdr *iph;
>         int room;
> @@ -691,7 +692,7 @@ void icmp_send(struct sk_buff *skb_in, int type, int code, __be32 info)
>                                           iph->tos;
>         mark = IP4_REPLY_MARK(net, skb_in->mark);
>
> -       if (ip_options_echo(net, &icmp_param.replyopts.opt.opt, skb_in))
> +       if (__ip_options_echo(net, &icmp_param.replyopts.opt.opt, skb_in, opt))
>                 goto out_unlock;
>
>
> @@ -742,7 +743,7 @@ void icmp_send(struct sk_buff *skb_in, int type, int code, __be32 info)
>         local_bh_enable();
>  out:;
>  }
> -EXPORT_SYMBOL(icmp_send);
> +EXPORT_SYMBOL(__icmp_send);
>
>
>  static void icmp_socket_deliver(struct sk_buff *skb, u32 info)
> --
>


-- 
paul moore
www.paul-moore.com

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