[PATCH 08/12] xfrm: use hlist_del_init_rcu for state_cache and state_cache_input

[Steffen Klassert <steffen.klassert@secunet.com>]

From: Siwei Zhang <fourdizhang@tencent.com>

Commit 14acf9652e56 ("xfrm: defensively unhash xfrm_state lists in
__xfrm_state_delete") converted bydst/bysrc/byseq/byspi from
hlist_del_rcu() to hlist_del_init_rcu() so that a second
__xfrm_state_delete() on the same object becomes a no-op rather than a
write through LIST_POISON pprev. It missed state_cache and
state_cache_input, which kept hlist_del_rcu():

- hlist_del_rcu() leaves pprev = LIST_POISON2 (non-NULL), so
  hlist_unhashed() returns false.
- hlist_del_init_rcu() leaves pprev = NULL, so hlist_unhashed()
  returns true.

A second __xfrm_state_delete() therefore enters __hlist_del() on the
already-deleted state_cache/state_cache_input nodes and does
WRITE_ONCE(*pprev, next) through LIST_POISON2 — a write use-after-free
once the slab is reused. The corruption can in turn cause a subsequent
hlist_for_each_entry_rcu traversal to follow a dangling next pointer,
producing the read use-after-free reported in xfrm_input_state_lookup().

Switch state_cache and state_cache_input to hlist_del_init_rcu() to
match the other four lists, closing the write use-after-free and, with
it, the read use-after-free it spawns.

Assisted-by: CodeBuddy:GLM-5.2
Fixes: 0045e3d80613 ("xfrm: Cache used outbound xfrm states at the policy.")
Fixes: 81a331a0e72d ("xfrm: Add an inbound percpu state cache.")
Cc: stable@vger.kernel.org
Signed-off-by: Siwei Zhang <fourdizhang@tencent.com>
Signed-off-by: Steffen Klassert <steffen.klassert@secunet.com>
---
 net/xfrm/xfrm_state.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/net/xfrm/xfrm_state.c b/net/xfrm/xfrm_state.c
index de097bba803b..e45aa1ed5b96 100644
--- a/net/xfrm/xfrm_state.c
+++ b/net/xfrm/xfrm_state.c
@@ -826,9 +826,9 @@ int __xfrm_state_delete(struct xfrm_state *x)
 		if (!hlist_unhashed(&x->byseq))
 			hlist_del_init_rcu(&x->byseq);
 		if (!hlist_unhashed(&x->state_cache))
-			hlist_del_rcu(&x->state_cache);
+			hlist_del_init_rcu(&x->state_cache);
 		if (!hlist_unhashed(&x->state_cache_input))
-			hlist_del_rcu(&x->state_cache_input);
+			hlist_del_init_rcu(&x->state_cache_input);
 
 		if (!hlist_unhashed(&x->byspi))
 			hlist_del_init_rcu(&x->byspi);
-- 
2.43.0