Registering the same notifier to a hook repeatedly can cause the hook
list to form a ring or lose other members of the list.
case1: An infinite loop in notifier_chain_register() can cause soft lockup
atomic_notifier_chain_register(&test_notifier_list, &test1);
atomic_notifier_chain_register(&test_notifier_list, &test1);
atomic_notifier_chain_register(&test_notifier_list, &test2);
case2: An infinite loop in notifier_chain_register() can cause soft lockup
atomic_notifier_chain_register(&test_notifier_list, &test1);
atomic_notifier_chain_register(&test_notifier_list, &test1);
atomic_notifier_call_chain(&test_notifier_list, 0, NULL);
case3: lose other hook test2
atomic_notifier_chain_register(&test_notifier_list, &test1);
atomic_notifier_chain_register(&test_notifier_list, &test2);
atomic_notifier_chain_register(&test_notifier_list, &test1);
case4: Unregister returns 0, but the hook is still in the linked list,
and it is not really registered. If you call notifier_call_chain
after ko is unloaded, it will trigger oops.
If the system is configured with softlockup_panic and the same
hook is repeatedly registered on the panic_notifier_list, it
will cause a loop panic.
Add a check in notifier_chain_register() to avoid duplicate registration
Signed-off-by: Xiaoming Ni <[email protected]>
---
kernel/notifier.c | 5 ++++-
1 file changed, 4 insertions(+), 1 deletion(-)
diff --git a/kernel/notifier.c b/kernel/notifier.c
index d9f5081..30bedb8 100644
--- a/kernel/notifier.c
+++ b/kernel/notifier.c
@@ -23,7 +23,10 @@ static int notifier_chain_register(struct notifier_block **nl,
struct notifier_block *n)
{
while ((*nl) != NULL) {
- WARN_ONCE(((*nl) == n), "double register detected");
+ if (unlikely((*nl) == n)) {
+ WARN(1, "double register detected");
+ return 0;
+ }
if (n->priority > (*nl)->priority)
break;
nl = &((*nl)->next);
--
1.8.5.6
blocking_notifier_chain_cond_register() does not consider
system_booting state, which is the only difference between this
function and blocking_notifier_cain_register(). This can be a bug
and is a piece of duplicate code.
Delete blocking_notifier_chain_cond_register()
Signed-off-by: Xiaoming Ni <[email protected]>
---
include/linux/notifier.h | 4 ----
kernel/notifier.c | 23 -----------------------
net/sunrpc/rpc_pipe.c | 2 +-
3 files changed, 1 insertion(+), 28 deletions(-)
diff --git a/include/linux/notifier.h b/include/linux/notifier.h
index 0096a05..0189476 100644
--- a/include/linux/notifier.h
+++ b/include/linux/notifier.h
@@ -150,10 +150,6 @@ extern int raw_notifier_chain_register(struct raw_notifier_head *nh,
extern int srcu_notifier_chain_register(struct srcu_notifier_head *nh,
struct notifier_block *nb);
-extern int blocking_notifier_chain_cond_register(
- struct blocking_notifier_head *nh,
- struct notifier_block *nb);
-
extern int atomic_notifier_chain_unregister(struct atomic_notifier_head *nh,
struct notifier_block *nb);
extern int blocking_notifier_chain_unregister(struct blocking_notifier_head *nh,
diff --git a/kernel/notifier.c b/kernel/notifier.c
index e3d221f..63d7501 100644
--- a/kernel/notifier.c
+++ b/kernel/notifier.c
@@ -221,29 +221,6 @@ int blocking_notifier_chain_register(struct blocking_notifier_head *nh,
EXPORT_SYMBOL_GPL(blocking_notifier_chain_register);
/**
- * blocking_notifier_chain_cond_register - Cond add notifier to a blocking notifier chain
- * @nh: Pointer to head of the blocking notifier chain
- * @n: New entry in notifier chain
- *
- * Adds a notifier to a blocking notifier chain, only if not already
- * present in the chain.
- * Must be called in process context.
- *
- * Currently always returns zero.
- */
-int blocking_notifier_chain_cond_register(struct blocking_notifier_head *nh,
- struct notifier_block *n)
-{
- int ret;
-
- down_write(&nh->rwsem);
- ret = notifier_chain_register(&nh->head, n);
- up_write(&nh->rwsem);
- return ret;
-}
-EXPORT_SYMBOL_GPL(blocking_notifier_chain_cond_register);
-
-/**
* blocking_notifier_chain_unregister - Remove notifier from a blocking notifier chain
* @nh: Pointer to head of the blocking notifier chain
* @n: Entry to remove from notifier chain
diff --git a/net/sunrpc/rpc_pipe.c b/net/sunrpc/rpc_pipe.c
index 126d314..1287f80 100644
--- a/net/sunrpc/rpc_pipe.c
+++ b/net/sunrpc/rpc_pipe.c
@@ -50,7 +50,7 @@
int rpc_pipefs_notifier_register(struct notifier_block *nb)
{
- return blocking_notifier_chain_cond_register(&rpc_pipefs_notifier_list, nb);
+ return blocking_notifier_chain_register(&rpc_pipefs_notifier_list, nb);
}
EXPORT_SYMBOL_GPL(rpc_pipefs_notifier_register);
--
1.8.5.6