ipv6: per-netns exclusive flowlabel checks

Ipv6 flowlabels historically require a reservation before use.
Optionally in exclusive mode (e.g., user-private).

Commit 3bba6acb6d03 ("ipv6: elide flowlabel check if no exclusive
leases exist") introduced a fastpath that avoids this check when no
exclusive leases exist in the system, and thus any flowlabel use
will be granted.

That allows skipping the control operation to reserve a flowlabel
entirely. Though with a warning if the fast path fails:

  This is an optimization. Robust applications still have to revert to
  requesting leases if the fast path fails due to an exclusive lease.

Still, this is subtle. Better isolate network namespaces from each
other. Flowlabels are per-netns. Also record per-netns whether
exclusive leases are in use. Then behavior does not change based on
activity in other netns.

Changes
  v2
    - wrap in IS_ENABLED(CONFIG_IPV6) to avoid breakage if disabled

Fixes: 3bba6acb6d03 ("ipv6: elide flowlabel check if no exclusive leases exist")
Link: https://lore.kernel.org/netdev/MWHPR2201MB1072BCCCFCE779E4094837ACD0329@MWHPR2201MB1072.namprd22.prod.outlook.com/
Reported-by: Congyu Liu <liu3101@purdue.edu>
Signed-off-by: Willem de Bruijn <willemb@google.com>
Tested-by: Congyu Liu <liu3101@purdue.edu>
Link: https://lore.kernel.org/r/20220215160037.1976072-1-willemdebruijn.kernel@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

diff --git a/include/net/ipv6.h b/include/net/ipv6.h
index 3afcb128e064911664b415c13d59bad5fc0547b4..92eec13d1693201d98e0f61fb94da42c64e4c483 100644 (file)
--- a/include/net/ipv6.h
+++ b/include/net/ipv6.h
@@ -393,17 +393,20 @@ static inline void txopt_put(struct ipv6_txoptions *opt)
                kfree_rcu(opt, rcu);
 }
 
+#if IS_ENABLED(CONFIG_IPV6)
 struct ip6_flowlabel *__fl6_sock_lookup(struct sock *sk, __be32 label);
 
 extern struct static_key_false_deferred ipv6_flowlabel_exclusive;
 static inline struct ip6_flowlabel *fl6_sock_lookup(struct sock *sk,
                                                    __be32 label)
 {
-       if (static_branch_unlikely(&ipv6_flowlabel_exclusive.key))
+       if (static_branch_unlikely(&ipv6_flowlabel_exclusive.key) &&
+           READ_ONCE(sock_net(sk)->ipv6.flowlabel_has_excl))
                return __fl6_sock_lookup(sk, label) ? : ERR_PTR(-ENOENT);
 
        return NULL;
 }
+#endif
 
 struct ipv6_txoptions *fl6_merge_options(struct ipv6_txoptions *opt_space,
                                         struct ip6_flowlabel *fl,

diff --git a/include/net/netns/ipv6.h b/include/net/netns/ipv6.h
index a4b55038031652601444e46006c489a4e23b0ab7..6bd7e5a85ce76c721b6cc9e7e08d41282066a170 100644 (file)
--- a/include/net/netns/ipv6.h
+++ b/include/net/netns/ipv6.h
@@ -77,9 +77,10 @@ struct netns_ipv6 {
        spinlock_t              fib6_gc_lock;
        unsigned int             ip6_rt_gc_expire;
        unsigned long            ip6_rt_last_gc;
+       unsigned char           flowlabel_has_excl;
 #ifdef CONFIG_IPV6_MULTIPLE_TABLES
-       unsigned int            fib6_rules_require_fldissect;
        bool                    fib6_has_custom_rules;
+       unsigned int            fib6_rules_require_fldissect;
 #ifdef CONFIG_IPV6_SUBTREES
        unsigned int            fib6_routes_require_src;
 #endif

diff --git a/net/ipv6/ip6_flowlabel.c b/net/ipv6/ip6_flowlabel.c
index aa673a6a7e4328d03e89527ed3daaccd69c39084..ceb85c67ce3952b7142eeec29bff46a7eaf5217b 100644 (file)
--- a/net/ipv6/ip6_flowlabel.c
+++ b/net/ipv6/ip6_flowlabel.c
@@ -450,8 +450,10 @@ fl_create(struct net *net, struct sock *sk, struct in6_flowlabel_req *freq,
                err = -EINVAL;
                goto done;
        }
-       if (fl_shared_exclusive(fl) || fl->opt)
+       if (fl_shared_exclusive(fl) || fl->opt) {
+               WRITE_ONCE(sock_net(sk)->ipv6.flowlabel_has_excl, 1);
                static_branch_deferred_inc(&ipv6_flowlabel_exclusive);
+       }
        return fl;
 
 done: