[PATCH 4.19 03/62] xfrm: xfrm_policy: fix a possible double xfrm_pols_put() in xfrm_bundle_lookup()

[Greg Kroah-Hartman]

From: Hangyu Hua <hbh25y@xxxxxxxxx>

[ Upstream commit f85daf0e725358be78dfd208dea5fd665d8cb901 ]

xfrm_policy_lookup() will call xfrm_pol_hold_rcu() to get a refcount of
pols[0]. This refcount can be dropped in xfrm_expand_policies() when
xfrm_expand_policies() return error. pols[0]'s refcount is balanced in
here. But xfrm_bundle_lookup() will also call xfrm_pols_put() with
num_pols == 1 to drop this refcount when xfrm_expand_policies() return
error.

This patch also fix an illegal address access. pols[0] will save a error
point when xfrm_policy_lookup fails. This lead to xfrm_pols_put to resolve
an illegal address in xfrm_bundle_lookup's error path.

Fix these by setting num_pols = 0 in xfrm_expand_policies()'s error path.

Fixes: 80c802f3073e ("xfrm: cache bundles instead of policies for outgoing flows")
Signed-off-by: Hangyu Hua <hbh25y@xxxxxxxxx>
Signed-off-by: Steffen Klassert <steffen.klassert@xxxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
 net/xfrm/xfrm_policy.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/net/xfrm/xfrm_policy.c b/net/xfrm/xfrm_policy.c
index bb1c94e20e82..3582f77bab6a 100644
--- a/net/xfrm/xfrm_policy.c
+++ b/net/xfrm/xfrm_policy.c
@@ -1697,8 +1697,10 @@ static int xfrm_expand_policies(const struct flowi *fl, u16 family,
 		*num_xfrms = 0;
 		return 0;
 	}
-	if (IS_ERR(pols[0]))
+	if (IS_ERR(pols[0])) {
+		*num_pols = 0;
 		return PTR_ERR(pols[0]);
+	}
 
 	*num_xfrms = pols[0]->xfrm_nr;
 
@@ -1713,6 +1715,7 @@ static int xfrm_expand_policies(const struct flowi *fl, u16 family,
 		if (pols[1]) {
 			if (IS_ERR(pols[1])) {
 				xfrm_pols_put(pols, *num_pols);
+				*num_pols = 0;
 				return PTR_ERR(pols[1]);
 			}
 			(*num_pols)++;
-- 
2.35.1