xfrm: policy: use atomic_inc_not_zero in rcu section

If we don't hold the policy lock anymore the refcnt might
already be 0, i.e. policy struct is about to be free'd.

Switch to atomic_inc_not_zero to avoid this.

On removal policies are already unlinked from the tables (lists)
before the last _put occurs so we are not supposed to find the same
'dead' entry on the next loop, so its safe to just repeat the lookup.

Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Steffen Klassert <steffen.klassert@secunet.com>

1 files changed, 7 insertions, 1 deletions

diff --git a/net/xfrm/xfrm_policy.c b/net/xfrm/xfrm_policy.c
index 576d90321068..09f2e2b38246 100644
--- a/net/xfrm/xfrm_policy.c
+++ b/net/xfrm/xfrm_policy.c
@@ -60,6 +60,11 @@ static void __xfrm_policy_link(struct xfrm_policy *pol, int dir);
 static struct xfrm_policy *__xfrm_policy_unlink(struct xfrm_policy *pol,
                                                 int dir);
 
+static inline bool xfrm_pol_hold_rcu(struct xfrm_policy *policy)
+{
+        return atomic_inc_not_zero(&policy->refcnt);
+}
+
 static inline bool
 __xfrm4_selector_match(const struct xfrm_selector *sel, const struct flowi *fl)
 {
@@ -1164,7 +1169,8 @@ static struct xfrm_policy *xfrm_policy_lookup_bytype(struct net *net, u8 type,
         if (read_seqcount_retry(&xfrm_policy_hash_generation, sequence))
                 goto retry;
 
-        xfrm_pol_hold(ret);
+        if (ret && !xfrm_pol_hold_rcu(ret))
+                goto retry;
 fail:
         read_unlock_bh(&net->xfrm.xfrm_policy_lock);