[PATCH AUTOSEL 6.18] xfrm: fix refcount leak in xfrm_migrate_policy_find

[Sasha Levin <sashal@kernel.org>]

From: Kotlyarov Mihail <mihailkotlyarow@gmail.com>

[ Upstream commit 83317cce60a032c49480dcdabe146435bd689d03 ]

syzkaller reported a memory leak in xfrm_policy_alloc:

  BUG: memory leak
  unreferenced object 0xffff888114d79000 (size 1024):
    comm "syz.1.17", pid 931
    ...
    xfrm_policy_alloc+0xb3/0x4b0 net/xfrm/xfrm_policy.c:432

The root cause is a double call to xfrm_pol_hold_rcu() in
xfrm_migrate_policy_find(). The lookup function already returns
a policy with held reference, making the second call redundant.

Remove the redundant xfrm_pol_hold_rcu() call to fix the refcount
imbalance and prevent the memory leak.

Found by Linux Verification Center (linuxtesting.org) with Syzkaller.

Fixes: 563d5ca93e88 ("xfrm: switch migrate to xfrm_policy_lookup_bytype")
Signed-off-by: Kotlyarov Mihail <mihailkotlyarow@gmail.com>
Reviewed-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Steffen Klassert <steffen.klassert@secunet.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---

LLM Generated explanations, may be completely bogus:

Error: Failed to generate final synthesis

 net/xfrm/xfrm_policy.c | 3 ---
 1 file changed, 3 deletions(-)

diff --git a/net/xfrm/xfrm_policy.c b/net/xfrm/xfrm_policy.c
index 4526c9078b136..29c94ee0ceb25 100644
--- a/net/xfrm/xfrm_policy.c
+++ b/net/xfrm/xfrm_policy.c
@@ -4528,9 +4528,6 @@ static struct xfrm_policy *xfrm_migrate_policy_find(const struct xfrm_selector *
 	pol = xfrm_policy_lookup_bytype(net, type, &fl, sel->family, dir, if_id);
 	if (IS_ERR_OR_NULL(pol))
 		goto out_unlock;
-
-	if (!xfrm_pol_hold_rcu(pol))
-		pol = NULL;
 out_unlock:
 	rcu_read_unlock();
 	return pol;
-- 
2.53.0