Re: [Patch net] ipt_CLUSTERIP: fix a refcount bug in clusterip_config_find_get()

On Thu, Feb 8, 2018 at 12:01 AM, Florian Westphal [off-list ref] wrote:

Cong Wang [off-list ref] wrote:

quoted

In clusterip_config_find_get() we hold RCU read lock so it could
run concurrently with clusterip_config_entry_put(), as a result,
the refcnt could go back to 1 from 0, which leads to a double
list_del()... Just replace refcount_inc() with
refcount_inc_not_zero(), as for c->refcount.

Fixes: d73f33b16883 ("netfilter: CLUSTERIP: RCU conversion")
Cc: Eric Dumazet <redacted>
Cc: Pablo Neira Ayuso <pablo@netfilter.org>
Signed-off-by: Cong Wang <redacted>
---
 net/ipv4/netfilter/ipt_CLUSTERIP.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/net/ipv4/netfilter/ipt_CLUSTERIP.c b/net/ipv4/netfilter/ipt_CLUSTERIP.c
index 1ff72b87a066..4537b1686c7c 100644
--- a/net/ipv4/netfilter/ipt_CLUSTERIP.c
+++ b/net/ipv4/netfilter/ipt_CLUSTERIP.c

@@ -154,8 +154,10 @@ clusterip_config_find_get(struct net *net, __be32 clusterip, int entry)
 #endif
              if (unlikely(!refcount_inc_not_zero(&c->refcount)))
                      c = NULL;
-             else if (entry)
-                     refcount_inc(&c->entries);
+             else if (entry) {
+                     if (unlikely(!refcount_inc_not_zero(&c->entries)))

this needs to call clusterip_config_put(c); too, else we leak one
reference.

Other than that this looks good.

Right, good catch! I will send v2.