net: tcp: add RTAX_CC_ALGO fib handling

This patch adds the minimum necessary for the RTAX_CC_ALGO congestion
control metric to be set up and dumped back to user space.

While the internal representation of RTAX_CC_ALGO is handled as a u32
key, we avoided to expose this implementation detail to user space, thus
instead, we chose the netlink attribute that is being exchanged between
user space to be the actual congestion control algorithm name, similarly
as in the setsockopt(2) API in order to allow for maximum flexibility,
even for 3rd party modules.

It is a bit unfortunate that RTAX_QUICKACK used up a whole RTAX slot as
it should have been stored in RTAX_FEATURES instead, we first thought
about reusing it for the congestion control key, but it brings more
complications and/or confusion than worth it.

Joint work with Florian Westphal.

Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Daniel Borkmann <dborkman@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 12 insertions, 2 deletions

diff --git a/net/ipv4/fib_semantics.c b/net/ipv4/fib_semantics.c
index f99f41bd15b8..d2b7b5521b1b 100644
--- a/net/ipv4/fib_semantics.c
+++ b/net/ipv4/fib_semantics.c
@@ -360,7 +360,8 @@ static inline size_t fib_nlmsg_size(struct fib_info *fi)
                          + nla_total_size(4) /* RTA_TABLE */
                          + nla_total_size(4) /* RTA_DST */
                          + nla_total_size(4) /* RTA_PRIORITY */
-                         + nla_total_size(4); /* RTA_PREFSRC */
+                         + nla_total_size(4) /* RTA_PREFSRC */
+                         + nla_total_size(TCP_CA_NAME_MAX); /* RTAX_CC_ALGO */
 
         /* space for nested metrics */
         payload += nla_total_size((RTAX_MAX * nla_total_size(4)));
@@ -859,7 +860,16 @@ struct fib_info *fib_create_info(struct fib_config *cfg)
 
                                 if (type > RTAX_MAX)
                                         goto err_inval;
-                                val = nla_get_u32(nla);
+                                if (type == RTAX_CC_ALGO) {
+                                        char tmp[TCP_CA_NAME_MAX];
+
+                                        nla_strlcpy(tmp, nla, sizeof(tmp));
+                                        val = tcp_ca_get_key_by_name(tmp);
+                                        if (val == TCP_CA_UNSPEC)
+                                                goto err_inval;
+                                } else {
+                                        val = nla_get_u32(nla);
+                                }
                                 if (type == RTAX_ADVMSS && val > 65535 - 40)
                                         val = 65535 - 40;
                                 if (type == RTAX_MTU && val > 65535 - 15)