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ipv6: grab rt->rt6i_ref before allocating pcpu rt 

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>
This commit is contained in:
Wei Wang 2017-10-06 12:06:04 -07:00 committed by David S. Miller
parent 2b760fcf5c
commit a94b9367e0
1 changed files with 30 additions and 30 deletions
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60
net/ipv6/route.c
View File

@ -1070,7 +1070,6 @@ 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);
@ -1081,28 +1080,20 @@ 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_release_immediate(&pcpu_rt->dst);
pcpu_rt = rt;
}
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);
/* release refcnt taken by above dst_hold() */
dst_release_immediate(&pcpu_rt->dst);
dst_hold(&prev->dst);
pcpu_rt = prev;
}
rt6_dst_from_metrics_check(pcpu_rt);
read_unlock_bh(&table->tb6_lock);
return pcpu_rt;
}
@ -1683,19 +1674,28 @@ redo_rt6_select:
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);