2019-07-10 03:09:58

by Xiaoming Ni

Subject: [PATCH v3 1/3] kernel/notifier.c: avoid duplicate registration

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

2019-07-17 11:20:06

by Vasily Averin

Subject: Re: [PATCH v3 1/3] kernel/notifier.c: avoid duplicate registration

On 7/10/19 6:09 AM, Xiaoming Ni wrote:
> 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]>
Reviewed-by: Vasily Averin <[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);
>