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Date: Fri, 6 Oct 2017 12:06:06 -0700
From: Wei Wang <weiwan@...gle.com>
To: David Miller <davem@...emloft.net>, netdev@...r.kernel.org
Cc: Eric Dumazet <edumazet@...gle.com>,
Martin KaFai Lau <kafai@...com>, Wei Wang <weiwan@...gle.com>
Subject: [PATCH net-next 11/16] ipv6: replace dst_hold() with dst_hold_safe() in routing code
From: Wei Wang <weiwan@...gle.com>
With rwlock, it is safe to call dst_hold() in the read thread because
read thread is guaranteed to be separated from write thread.
However, after we replace rwlock with rcu, it is no longer safe to use
dst_hold(). A dst might already have been deleted but is waiting for the
rcu grace period to pass before freeing the memory when a read thread is
trying to do dst_hold(). This could potentially cause double free issue.
So this commit replaces all dst_hold() with dst_hold_safe() in all read
thread to avoid this double free issue.
And in order to make the code more compact, a new function ip6_hold_safe()
is introduced. It calls dst_hold_safe() first, and if that fails, it will
either fall back to hold and return net->ipv6.ip6_null_entry or set rt to
NULL according to the caller's need.
Signed-off-by: Wei Wang <weiwan@...gle.com>
Signed-off-by: Martin KaFai Lau <kafai@...com>
Signed-off-by: Eric Dumazet <edumazet@...gle.com>
---
net/ipv6/addrconf.c | 3 ++-
net/ipv6/route.c | 71 +++++++++++++++++++++++++++++++++++++++--------------
2 files changed, 54 insertions(+), 20 deletions(-)
diff --git a/net/ipv6/addrconf.c b/net/ipv6/addrconf.c
index 873afafddfc4..f86e931d555e 100644
--- a/net/ipv6/addrconf.c
+++ b/net/ipv6/addrconf.c
@@ -2333,7 +2333,8 @@ static struct rt6_info *addrconf_get_prefix_route(const struct in6_addr *pfx,
continue;
if ((rt->rt6i_flags & noflags) != 0)
continue;
- dst_hold(&rt->dst);
+ if (!dst_hold_safe(&rt->dst))
+ rt = NULL;
break;
}
out:
diff --git a/net/ipv6/route.c b/net/ipv6/route.c
index 941c062389d2..aeb349aea429 100644
--- a/net/ipv6/route.c
+++ b/net/ipv6/route.c
@@ -874,6 +874,23 @@ static struct fib6_node* fib6_backtrack(struct fib6_node *fn,
}
}
+static bool ip6_hold_safe(struct net *net, struct rt6_info **prt,
+ bool null_fallback)
+{
+ struct rt6_info *rt = *prt;
+
+ if (dst_hold_safe(&rt->dst))
+ return true;
+ if (null_fallback) {
+ rt = net->ipv6.ip6_null_entry;
+ dst_hold(&rt->dst);
+ } else {
+ rt = NULL;
+ }
+ *prt = rt;
+ return false;
+}
+
static struct rt6_info *ip6_pol_route_lookup(struct net *net,
struct fib6_table *table,
struct flowi6 *fl6, int flags)
@@ -898,7 +915,9 @@ static struct rt6_info *ip6_pol_route_lookup(struct net *net,
if (rt_cache)
rt = rt_cache;
- dst_use(&rt->dst, jiffies);
+ if (ip6_hold_safe(net, &rt, true))
+ dst_use_noref(&rt->dst, jiffies);
+
read_unlock_bh(&table->tb6_lock);
trace_fib6_table_lookup(net, rt, table->tb6_id, fl6);
@@ -1061,10 +1080,9 @@ static struct rt6_info *rt6_get_pcpu_route(struct rt6_info *rt)
p = this_cpu_ptr(rt->rt6i_pcpu);
pcpu_rt = *p;
- if (pcpu_rt) {
- dst_hold(&pcpu_rt->dst);
+ if (pcpu_rt && ip6_hold_safe(NULL, &pcpu_rt, false))
rt6_dst_from_metrics_check(pcpu_rt);
- }
+
return pcpu_rt;
}
@@ -1625,12 +1643,17 @@ struct rt6_info *ip6_pol_route(struct net *net, struct fib6_table *table,
if (rt_cache)
rt = rt_cache;
- if (rt == net->ipv6.ip6_null_entry || (rt->rt6i_flags & RTF_CACHE)) {
- dst_use(&rt->dst, jiffies);
+ if (rt == net->ipv6.ip6_null_entry) {
+ read_unlock_bh(&table->tb6_lock);
+ dst_hold(&rt->dst);
+ trace_fib6_table_lookup(net, rt, table->tb6_id, fl6);
+ return rt;
+ } else if (rt->rt6i_flags & RTF_CACHE) {
+ if (ip6_hold_safe(net, &rt, true)) {
+ dst_use_noref(&rt->dst, jiffies);
+ rt6_dst_from_metrics_check(rt);
+ }
read_unlock_bh(&table->tb6_lock);
-
- rt6_dst_from_metrics_check(rt);
-
trace_fib6_table_lookup(net, rt, table->tb6_id, fl6);
return rt;
} else if (unlikely((fl6->flowi6_flags & FLOWI_FLAG_KNOWN_NH) &&
@@ -1643,7 +1666,13 @@ struct rt6_info *ip6_pol_route(struct net *net, struct fib6_table *table,
struct rt6_info *uncached_rt;
- dst_use(&rt->dst, jiffies);
+ if (ip6_hold_safe(net, &rt, true)) {
+ dst_use_noref(&rt->dst, jiffies);
+ } else {
+ read_unlock_bh(&table->tb6_lock);
+ uncached_rt = rt;
+ goto uncached_rt_out;
+ }
read_unlock_bh(&table->tb6_lock);
uncached_rt = ip6_rt_cache_alloc(rt, &fl6->daddr, NULL);
@@ -1659,6 +1688,7 @@ struct rt6_info *ip6_pol_route(struct net *net, struct fib6_table *table,
dst_hold(&uncached_rt->dst);
}
+uncached_rt_out:
trace_fib6_table_lookup(net, uncached_rt, table->tb6_id, fl6);
return uncached_rt;
@@ -1667,8 +1697,7 @@ struct rt6_info *ip6_pol_route(struct net *net, struct fib6_table *table,
struct rt6_info *pcpu_rt;
- rt->dst.lastuse = jiffies;
- rt->dst.__use++;
+ dst_use_noref(&rt->dst, jiffies);
pcpu_rt = rt6_get_pcpu_route(rt);
if (pcpu_rt) {
@@ -2130,7 +2159,7 @@ static struct rt6_info *__ip6_route_redirect(struct net *net,
}
out:
- dst_hold(&rt->dst);
+ ip6_hold_safe(net, &rt, true);
read_unlock_bh(&table->tb6_lock);
@@ -2841,7 +2870,8 @@ static int ip6_route_del(struct fib6_config *cfg,
continue;
if (cfg->fc_protocol && cfg->fc_protocol != rt->rt6i_protocol)
continue;
- dst_hold(&rt->dst);
+ if (!dst_hold_safe(&rt->dst))
+ break;
read_unlock_bh(&table->tb6_lock);
/* if gateway was specified only delete the one hop */
@@ -3038,7 +3068,7 @@ static struct rt6_info *rt6_get_route_info(struct net *net,
continue;
if (!ipv6_addr_equal(&rt->rt6i_gateway, gwaddr))
continue;
- dst_hold(&rt->dst);
+ ip6_hold_safe(NULL, &rt, false);
break;
}
out:
@@ -3096,7 +3126,7 @@ struct rt6_info *rt6_get_dflt_router(const struct in6_addr *addr, struct net_dev
break;
}
if (rt)
- dst_hold(&rt->dst);
+ ip6_hold_safe(NULL, &rt, false);
read_unlock_bh(&table->tb6_lock);
return rt;
}
@@ -3139,9 +3169,12 @@ static void __rt6_purge_dflt_routers(struct fib6_table *table)
for (rt = table->tb6_root.leaf; rt; rt = rt->dst.rt6_next) {
if (rt->rt6i_flags & (RTF_DEFAULT | RTF_ADDRCONF) &&
(!rt->rt6i_idev || rt->rt6i_idev->cnf.accept_ra != 2)) {
- dst_hold(&rt->dst);
- read_unlock_bh(&table->tb6_lock);
- ip6_del_rt(rt);
+ if (dst_hold_safe(&rt->dst)) {
+ read_unlock_bh(&table->tb6_lock);
+ ip6_del_rt(rt);
+ } else {
+ read_unlock_bh(&table->tb6_lock);
+ }
goto restart;
}
}
--
2.14.2.920.gcf0c67979c-goog
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