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        Viresh Kumar <viresh.kumar@linaro.org>,
        YueHaibing <yuehaibing@huawei.com>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Sasha Levin <sashal@kernel.org>
Subject: [PATCH 5.4 069/388] kernel/notifier.c: intercept duplicate registrations to avoid infinite loops
Date:   Tue, 29 Sep 2020 12:56:40 +0200
Message-Id: <20200929110013.833689836@linuxfoundation.org>
In-Reply-To: <20200929110010.467764689@linuxfoundation.org>
References: <20200929110010.467764689@linuxfoundation.org>
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From: Xiaoming Ni <nixiaoming@huawei.com>

[ Upstream commit 1a50cb80f219c44adb6265f5071b81fc3c1deced ]

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/1568861888-34045-2-git-send-email-nixiaoming@huawei.com
Signed-off-by: Xiaoming Ni <nixiaoming@huawei.com>
Reviewed-by: Vasily Averin <vvs@virtuozzo.com>
Reviewed-by: Andrew Morton <akpm@linux-foundation.org>
Cc: Alexey Dobriyan <adobriyan@gmail.com>
Cc: Anna Schumaker <anna.schumaker@netapp.com>
Cc: Arjan van de Ven <arjan@linux.intel.com>
Cc: J. Bruce Fields <bfields@fieldses.org>
Cc: Chuck Lever <chuck.lever@oracle.com>
Cc: David S. Miller <davem@davemloft.net>
Cc: Jeff Layton <jlayton@kernel.org>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Nadia Derbey <Nadia.Derbey@bull.net>
Cc: "Paul E. McKenney" <paulmck@kernel.org>
Cc: Sam Protsenko <semen.protsenko@linaro.org>
Cc: Alan Stern <stern@rowland.harvard.edu>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Trond Myklebust <trond.myklebust@hammerspace.com>
Cc: Viresh Kumar <viresh.kumar@linaro.org>
Cc: Xiaoming Ni <nixiaoming@huawei.com>
Cc: YueHaibing <yuehaibing@huawei.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 kernel/notifier.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/kernel/notifier.c b/kernel/notifier.c
index 157d7c29f7207..f6d5ffe4e72ec 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);
-- 
2.25.1