netdev - Re: Kernel memory corruption in CIPSO labeled TCP packets processing.

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Date:   Wed, 30 Jan 2019 16:11:42 +0300
From:   Nazarov Sergey <s-nazarov@...dex.ru>
To:     Paul Moore <paul@...l-moore.com>
Cc:     "linux-security-module@...r.kernel.org" 
        <linux-security-module@...r.kernel.org>,
        "selinux@...r.kernel.org" <selinux@...r.kernel.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        Casey Schaufler <casey@...aufler-ca.com>
Subject: Re: Kernel memory corruption in CIPSO labeled TCP packets processing.

30.01.2019, 01:42, "Paul Moore" <paul@...l-moore.com>:
> There are several cases where the stack ends up calling icmp_send()
> after the skb has been through ip_options_compile(), that should be
> okay.
>
> --
> paul moore
> www.paul-moore.com

In those cases precompiled ip_options struct used, without the need to reuse ip_options_compile.
I think, for error ICMP packet, we can discard all other options except CIPSO. It will be better, than
send packet, contains wrong option's data. Modified patch 2:
---
 net/ipv4/cipso_ipv4.c |   24 ++++++++++++++++++++++--
 1 files changed, 22 insertions(+), 2 deletions(-)

diff --git a/net/ipv4/cipso_ipv4.c b/net/ipv4/cipso_ipv4.c
index 777fa3b..797826c 100644
--- a/net/ipv4/cipso_ipv4.c
+++ b/net/ipv4/cipso_ipv4.c
@@ -1735,13 +1735,33 @@ int cipso_v4_validate(const struct sk_buff *skb, unsigned char **option)
  */
 void cipso_v4_error(struct sk_buff *skb, int error, u32 gateway)
 {
+       struct ip_options opt;
+       unsigned char *optptr;
+
        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.
+        *
+        * For the generated ICMP packet, we create a
+        * temporary ip _options structure, contains
+        * the CIPSO option only, since the other options data
+        * could be modified when the original packet receiving.
+        */
+
+       memset(&opt, 0, sizeof(struct ip_options));
+       optptr = cipso_v4_optptr(skb);
+       if (optptr) {
+               opt.optlen = optptr[1];
+               opt.cipso = optptr - skb_network_header(skb);
+       }
+
        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);
 }
 
 /**