Received-SPF: pass (google.com: best guess record for domain of linux-nfs-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
From:   Xiaoming Ni <nixiaoming@huawei.com>
To:     <gregkh@linuxfoundation.org>, <akpm@linux-foundation.org>,
        <vvs@virtuozzo.com>, <torvalds@linux-foundation.org>,
        <adobriyan@gmail.com>, <anna.schumaker@netapp.com>,
        <arjan@linux.intel.com>, <bfields@fieldses.org>,
        <chuck.lever@oracle.com>, <davem@davemloft.net>,
        <jlayton@kernel.org>, <luto@kernel.org>, <mingo@kernel.org>,
        <Nadia.Derbey@bull.net>, <paulmck@linux.vnet.ibm.com>,
        <semen.protsenko@linaro.org>, <stern@rowland.harvard.edu>,
        <tglx@linutronix.de>, <trond.myklebust@hammerspace.com>,
        <viresh.kumar@linaro.org>
CC:     <stable@kernel.org>, <dylix.dailei@huawei.com>,
        <nixiaoming@huawei.com>, <yuehaibing@huawei.com>,
        <linux-kernel@vger.kernel.org>, <linux-nfs@vger.kernel.org>,
        <netdev@vger.kernel.org>
Subject: [PATCH v4 1/3] kernel/notifier.c: intercepting duplicate registrations to avoid infinite loops
Date:   Thu, 19 Sep 2019 10:58:06 +0800
Message-ID: <1568861888-34045-2-git-send-email-nixiaoming@huawei.com>
In-Reply-To: <1568861888-34045-1-git-send-email-nixiaoming@huawei.com>
References: <1568861888-34045-1-git-send-email-nixiaoming@huawei.com>
MIME-Version: 1.0
Content-Type: text/plain
Sender: linux-nfs-owner@vger.kernel.org
Precedence: bulk

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(-)

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