From: Willem de Bruijn willemb@google.com
commit 0b0dff5b3b98c5c7ce848151df9da0b3cdf0cc8b upstream.
Ipv6 flowlabels historically require a reservation before use. Optionally in exclusive mode (e.g., user-private).
Commit 59c820b2317f ("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: 59c820b2317f ("ipv6: elide flowlabel check if no exclusive leases exist") Link: https://lore.kernel.org/netdev/MWHPR2201MB1072BCCCFCE779E4094837ACD0329@MWHP... 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@gma... Signed-off-by: Jakub Kicinski kuba@kernel.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- include/net/ipv6.h | 5 ++++- include/net/netns/ipv6.h | 3 ++- net/ipv6/ip6_flowlabel.c | 4 +++- 3 files changed, 9 insertions(+), 3 deletions(-)
--- a/include/net/ipv6.h +++ b/include/net/ipv6.h @@ -390,17 +390,20 @@ static inline void txopt_put(struct ipv6 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, --- a/include/net/netns/ipv6.h +++ b/include/net/netns/ipv6.h @@ -80,9 +80,10 @@ 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 --- a/net/ipv6/ip6_flowlabel.c +++ b/net/ipv6/ip6_flowlabel.c @@ -450,8 +450,10 @@ fl_create(struct net *net, struct sock * 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: