[v4,1/3] kernel/notifier.c: intercepting duplicate registrations to avoid infinite loops
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Message ID 1568861888-34045-2-git-send-email-nixiaoming@huawei.com
State New
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Series
  • kernel/notifier.c: intercepting duplicate registrations to avoid infinite loops
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Commit Message

Xiaoming Ni Sept. 19, 2019, 2:58 a.m. UTC
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(),
Intercepting duplicate registrations to avoid infinite loops

Signed-off-by: Xiaoming Ni <nixiaoming@huawei.com>
Reviewed-by: Vasily Averin <vvs@virtuozzo.com>
---
 kernel/notifier.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

Comments

Greg KH Sept. 19, 2019, 6:36 a.m. UTC | #1
On Thu, Sep 19, 2019 at 10:58:06AM +0800, 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(),
> Intercepting duplicate registrations to avoid infinite loops
> 
> Signed-off-by: Xiaoming Ni <nixiaoming@huawei.com>
> Reviewed-by: Vasily Averin <vvs@virtuozzo.com>
> ---
>  kernel/notifier.c | 5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)

<formletter>

This is not the correct way to submit patches for inclusion in the
stable kernel tree.  Please read:
    https://www.kernel.org/doc/html/latest/process/stable-kernel-rules.html
for how to do this properly.

</formletter>

Same thing goes for all of the patches in this series.

thanks,

greg k-h
Xiaoming Ni Sept. 19, 2019, 12:55 p.m. UTC | #2
On 2019/9/19 14:36, Greg KH wrote:
> On Thu, Sep 19, 2019 at 10:58:06AM +0800, 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(),
>> Intercepting duplicate registrations to avoid infinite loops
>>
>> Signed-off-by: Xiaoming Ni <nixiaoming@huawei.com>
>> Reviewed-by: Vasily Averin <vvs@virtuozzo.com>
>> ---
>>  kernel/notifier.c | 5 ++++-
>>  1 file changed, 4 insertions(+), 1 deletion(-)
> 
> <formletter>
> 
> This is not the correct way to submit patches for inclusion in the
> stable kernel tree.  Please read:
>     https://www.kernel.org/doc/html/latest/process/stable-kernel-rules.html
> for how to do this properly.
> 
thanks for your guidance
I thought that as long as the code exists in the stable branch, it should be copied to stable@kernel.org
it is my mistake,

These patches are intended to be sent to the main line.
Should I resend it again?

> </formletter>
> 
> Same thing goes for all of the patches in this series.
> 
> thanks,
> 
> greg k-h
> 
> .
> 

thanks

Xiaoming Ni

Patch
diff mbox series

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);