linux-kernel - [PATCH] PCI: hotplug: fix null-ptr-dereferencd in cpcihp error path

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Date:   Sun, 21 Mar 2021 01:51:08 -0400
From:   Tong Zhang <ztong0001@...il.com>
To:     Scott Murray <scott@...teful.org>,
        Bjorn Helgaas <bhelgaas@...gle.com>, linux-pci@...r.kernel.org,
        linux-kernel@...r.kernel.org
Cc:     Tong Zhang <ztong0001@...il.com>
Subject: [PATCH] PCI: hotplug: fix null-ptr-dereferencd in cpcihp error path

There is an issue in the error path, which cpci_thread may remain NULL.
Calling kthread_stop(cpci_thread) will trigger a BUG().
It is better to check whether the thread is really created and started
before stop it.

[    1.292859] BUG: kernel NULL pointer dereference, address: 0000000000000028
[    1.293252] #PF: supervisor write access in kernel mode
[    1.293533] #PF: error_code(0x0002) - not-present page
[    1.295163] RIP: 0010:kthread_stop+0x22/0x170
[    1.300491] Call Trace:
[    1.300628]  cpci_hp_unregister_controller+0xf6/0x130
[    1.300906]  zt5550_hc_init_one+0x27a/0x27f [cpcihp_zt5550]

Signed-off-by: Tong Zhang <ztong0001@...il.com>
---
 drivers/pci/hotplug/cpci_hotplug_core.c | 12 ++++++------
 1 file changed, 6 insertions(+), 6 deletions(-)

diff --git a/drivers/pci/hotplug/cpci_hotplug_core.c b/drivers/pci/hotplug/cpci_hotplug_core.c
index d0559d2faf50..b44da397d631 100644
--- a/drivers/pci/hotplug/cpci_hotplug_core.c
+++ b/drivers/pci/hotplug/cpci_hotplug_core.c
@@ -47,7 +47,7 @@ static atomic_t extracting;
 int cpci_debug;
 static struct cpci_hp_controller *controller;
 static struct task_struct *cpci_thread;
-static int thread_finished;
+static int thread_started;
 
 static int enable_slot(struct hotplug_slot *slot);
 static int disable_slot(struct hotplug_slot *slot);
@@ -447,7 +447,7 @@ event_thread(void *data)
 				msleep(500);
 			} else if (rc < 0) {
 				dbg("%s - error checking slots", __func__);
-				thread_finished = 1;
+				thread_started = 0;
 				goto out;
 			}
 		} while (atomic_read(&extracting) && !kthread_should_stop());
@@ -479,7 +479,7 @@ poll_thread(void *data)
 					msleep(500);
 				} else if (rc < 0) {
 					dbg("%s - error checking slots", __func__);
-					thread_finished = 1;
+					thread_started = 0;
 					goto out;
 				}
 			} while (atomic_read(&extracting) && !kthread_should_stop());
@@ -501,7 +501,7 @@ cpci_start_thread(void)
 		err("Can't start up our thread");
 		return PTR_ERR(cpci_thread);
 	}
-	thread_finished = 0;
+	thread_started = 1;
 	return 0;
 }
 
@@ -509,7 +509,7 @@ static void
 cpci_stop_thread(void)
 {
 	kthread_stop(cpci_thread);
-	thread_finished = 1;
+	thread_started = 0;
 }
 
 int
@@ -571,7 +571,7 @@ cpci_hp_unregister_controller(struct cpci_hp_controller *old_controller)
 	int status = 0;
 
 	if (controller) {
-		if (!thread_finished)
+		if (thread_started)
 			cpci_stop_thread();
 		if (controller->irq)
 			free_irq(controller->irq, controller->dev_id);
-- 
2.25.1