From: Wei Wang weiwan@google.com
[ Upstream commit a94b9367e044ba672c9f4105eb1516ff6ff4948a ]
After rwlock is replaced with rcu and spinlock, ip6_pol_route() will be called with only rcu held. That means rt6 route deletion could happen simultaneously with rt6_make_pcpu_rt(). This could potentially cause memory leak if rt6_release() is called right before rt6_make_pcpu_rt() on the same route.
This patch grabs rt->rt6i_ref safely before calling rt6_make_pcpu_rt() to make sure rt6_release() will not get triggered while rt6_make_pcpu_rt() is in progress. And rt6_release() is called after rt6_make_pcpu_rt() is finished.
Note: As we are incrementing rt->rt6i_ref in ip6_pol_route(), there is a very slim chance that fib6_purge_rt() will be triggered unnecessarily when deleting a route if ip6_pol_route() running on another thread picks this route as well and tries to make pcpu cache for it.
Signed-off-by: Wei Wang weiwan@google.com Signed-off-by: Martin KaFai Lau kafai@fb.com Signed-off-by: Eric Dumazet edumazet@google.com Signed-off-by: David S. Miller davem@davemloft.net Signed-off-by: Sasha Levin alexander.levin@verizon.com --- net/ipv6/route.c | 58 ++++++++++++++++++++++++++++---------------------------- 1 file changed, 29 insertions(+), 29 deletions(-)
diff --git a/net/ipv6/route.c b/net/ipv6/route.c index a96d5b385d8f..406037b336aa 100644 --- a/net/ipv6/route.c +++ b/net/ipv6/route.c @@ -1055,7 +1055,6 @@ static struct rt6_info *rt6_get_pcpu_route(struct rt6_info *rt)
static struct rt6_info *rt6_make_pcpu_route(struct rt6_info *rt) { - struct fib6_table *table = rt->rt6i_table; struct rt6_info *pcpu_rt, *prev, **p;
pcpu_rt = ip6_rt_pcpu_alloc(rt); @@ -1066,28 +1065,20 @@ static struct rt6_info *rt6_make_pcpu_route(struct rt6_info *rt) return net->ipv6.ip6_null_entry; }
- read_lock_bh(&table->tb6_lock); - if (rt->rt6i_pcpu) { - p = this_cpu_ptr(rt->rt6i_pcpu); - prev = cmpxchg(p, NULL, pcpu_rt); - if (prev) { - /* If someone did it before us, return prev instead */ - dst_release_immediate(&pcpu_rt->dst); - pcpu_rt = prev; - } - } else { - /* rt has been removed from the fib6 tree - * before we have a chance to acquire the read_lock. - * In this case, don't brother to create a pcpu rt - * since rt is going away anyway. The next - * dst_check() will trigger a re-lookup. - */ + dst_hold(&pcpu_rt->dst); + p = this_cpu_ptr(rt->rt6i_pcpu); + prev = cmpxchg(p, NULL, pcpu_rt); + if (prev) { + /* If someone did it before us, return prev instead */ + /* release refcnt taken by ip6_rt_pcpu_alloc() */ dst_release_immediate(&pcpu_rt->dst); - pcpu_rt = rt; + /* release refcnt taken by above dst_hold() */ + dst_release_immediate(&pcpu_rt->dst); + dst_hold(&prev->dst); + pcpu_rt = prev; } - dst_hold(&pcpu_rt->dst); + rt6_dst_from_metrics_check(pcpu_rt); - read_unlock_bh(&table->tb6_lock); return pcpu_rt; }
@@ -1177,19 +1168,28 @@ struct rt6_info *ip6_pol_route(struct net *net, struct fib6_table *table, if (pcpu_rt) { read_unlock_bh(&table->tb6_lock); } else { - /* We have to do the read_unlock first - * because rt6_make_pcpu_route() may trigger - * ip6_dst_gc() which will take the write_lock. - */ - dst_hold(&rt->dst); - read_unlock_bh(&table->tb6_lock); - pcpu_rt = rt6_make_pcpu_route(rt); - dst_release(&rt->dst); + /* atomic_inc_not_zero() is needed when using rcu */ + if (atomic_inc_not_zero(&rt->rt6i_ref)) { + /* We have to do the read_unlock first + * because rt6_make_pcpu_route() may trigger + * ip6_dst_gc() which will take the write_lock. + * + * No dst_hold() on rt is needed because grabbing + * rt->rt6i_ref makes sure rt can't be released. + */ + read_unlock_bh(&table->tb6_lock); + pcpu_rt = rt6_make_pcpu_route(rt); + rt6_release(rt); + } else { + /* rt is already removed from tree */ + read_unlock_bh(&table->tb6_lock); + pcpu_rt = net->ipv6.ip6_null_entry; + dst_hold(&pcpu_rt->dst); + } }
trace_fib6_table_lookup(net, pcpu_rt, table->tb6_id, fl6); return pcpu_rt; - } } EXPORT_SYMBOL_GPL(ip6_pol_route);