[PATCH v1 2/2] net: xfrm: Use sequence counter with associated spinlock

From: Ahmed S. Darwish
Date: Tue Mar 16 2021 - 06:58:34 EST

A sequence counter write section must be serialized or its internal
state can get corrupted. A plain seqcount_t does not contain the
information of which lock must be held to guaranteee write side

For xfrm_state_hash_generation, use seqcount_spinlock_t instead of plain
seqcount_t. This allows to associate the spinlock used for write
serialization with the sequence counter. It thus enables lockdep to
verify that the write serialization lock is indeed held before entering
the sequence counter write section.

If lockdep is disabled, this lock association is compiled out and has
neither storage size nor runtime overhead.

Signed-off-by: Ahmed S. Darwish <a.darwish@xxxxxxxxxxxxx>
include/net/netns/xfrm.h | 2 +-
net/xfrm/xfrm_state.c | 3 ++-
2 files changed, 3 insertions(+), 2 deletions(-)

diff --git a/include/net/netns/xfrm.h b/include/net/netns/xfrm.h
index b59d73d529ba..e816b6a3ef2b 100644
--- a/include/net/netns/xfrm.h
+++ b/include/net/netns/xfrm.h
@@ -73,7 +73,7 @@ struct netns_xfrm {
struct dst_ops xfrm6_dst_ops;
spinlock_t xfrm_state_lock;
- seqcount_t xfrm_state_hash_generation;
+ seqcount_spinlock_t xfrm_state_hash_generation;

spinlock_t xfrm_policy_lock;
struct mutex xfrm_cfg_mutex;
diff --git a/net/xfrm/xfrm_state.c b/net/xfrm/xfrm_state.c
index ffd315cff984..4496f7efa220 100644
--- a/net/xfrm/xfrm_state.c
+++ b/net/xfrm/xfrm_state.c
@@ -2665,7 +2665,8 @@ int __net_init xfrm_state_init(struct net *net)
net->xfrm.state_num = 0;
INIT_WORK(&net->xfrm.state_hash_work, xfrm_hash_resize);
- seqcount_init(&net->xfrm.xfrm_state_hash_generation);
+ seqcount_spinlock_init(&net->xfrm.xfrm_state_hash_generation,
+ &net->xfrm.xfrm_state_lock);
return 0;