netdev - Re: [PATCH net-next] inet_diag: report TCP MD5 signing keys and addresses

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Message-ID: <1503544822.2499.73.camel@edumazet-glaptop3.roam.corp.google.com>
Date:   Wed, 23 Aug 2017 20:20:22 -0700
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     Ivan Delalande <colona@...sta.com>
Cc:     David Miller <davem@...emloft.net>, netdev@...r.kernel.org
Subject: Re: [PATCH net-next] inet_diag: report TCP MD5 signing keys and
 addresses

On Thu, 2017-08-24 at 03:22 +0200, Ivan Delalande wrote:
> Report TCP MD5 (RFC2385) signing keys, addresses and address prefixes to
> processes with CAP_NET_ADMIN requesting INET_DIAG_INFO. Currently it is
> not possible to retrieve these from the kernel once they have been
> configured on sockets.

I really find that all these changes in net/ipv4/inet_diag.c
for TCP stuff (and #ifdef CONFIG_TCP_MD5SIG all over the places) are
ugly.

Also, since you do not lock the socket, inet_diag_put_md5sig()
might see different lists (&md5sig->head) and you could either write non
reserved memory, or at the contrary report not initialized kernel data
to user.

+static int inet_diag_put_md5sig(struct sk_buff *skb,
+                               const struct tcp_md5sig_info *md5sig)
+{
+       const struct tcp_md5sig_key *key;
+       struct nlattr *attr;
+       struct tcp_md5sig *info = NULL;
+       int md5sig_count = 0;
+
+       hlist_for_each_entry_rcu(key, &md5sig->head, node)
+               md5sig_count++;
+
+       attr = nla_reserve(skb, INET_DIAG_MD5SIG,
+                          md5sig_count * sizeof(struct tcp_md5sig));
+       if (!attr)
+               return -EMSGSIZE;
+
+       info = nla_data(attr);
+       hlist_for_each_entry_rcu(key, &md5sig->head, node) {
+               inet_diag_md5sig_fill(info, key);
+               info++;

Here we might see different keys than computed (in md5sig_count)

+       }
+
+       return 0;
+}
+#endif
+