[19/86] kernel/notifier.c: intercept duplicate registrations to avoid infinite loops

Commit Message

Andrew Morton Dec. 5, 2019, 12:50 a.m. UTC

From: Xiaoming Ni <[e-mail]>
Subject: kernel/notifier.c: intercept duplicate registrations to avoid infinite loops

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

Link: http://lkml.kernel.org/r/[e-mail]
Signed-off-by: Xiaoming Ni <[e-mail]>
Reviewed-by: Vasily Averin <[e-mail]>
Reviewed-by: Andrew Morton <[e-mail]>
Cc: Alexey Dobriyan <[e-mail]>
Cc: Anna Schumaker <[e-mail]>
Cc: Arjan van de Ven <[e-mail]>
Cc: J. Bruce Fields <[e-mail]>
Cc: Chuck Lever <[e-mail]>
Cc: David S. Miller <[e-mail]>
Cc: Jeff Layton <[e-mail]>
Cc: Andy Lutomirski <[e-mail]>
Cc: Ingo Molnar <[e-mail]>
Cc: Nadia Derbey <[e-mail]>
Cc: "Paul E. McKenney" <[e-mail]>
Cc: Sam Protsenko <[e-mail]>
Cc: Alan Stern <[e-mail]>
Cc: Thomas Gleixner <[e-mail]>
Cc: Trond Myklebust <[e-mail]>
Cc: Viresh Kumar <[e-mail]>
Cc: Xiaoming Ni <[e-mail]>
Cc: YueHaibing <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
---

 kernel/notifier.c |    5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

Patch

--- a/kernel/notifier.c~kernel-notifierc-intercepting-duplicate-registrations-to-avoid-infinite-loops
+++ a/kernel/notifier.c
@@ -23,7 +23,10 @@  static int notifier_chain_register(struc
 		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);