[PATCH] usb: core: safely deal with the dynamic quirk lists

[Harry Pan]

Applying dynamic usbcore quirks in early booting when the slab is
not yet ready would cause kernel panic of null pointer dereference
because the quirk_count has been counted as 1 while the quirk_list
was failed to allocate.

i.e.,
[    1.044970] BUG: unable to handle kernel NULL pointer dereference at           (null)
[    1.044995] IP: [<ffffffffb0953ec7>] usb_detect_quirks+0x88/0xd1
[    1.045016] PGD 0
[    1.045026] Oops: 0000 [#1] PREEMPT SMP
[    1.046986] gsmi: Log Shutdown Reason 0x03
[    1.046995] Modules linked in:
[    1.047008] CPU: 0 PID: 81 Comm: kworker/0:3 Not tainted 4.4.154 #28
[    1.047016] Hardware name: Google Coral/Coral, BIOS Google_Coral.10068.27.0 12/04/2017
[    1.047028] Workqueue: usb_hub_wq hub_event
[    1.047037] task: ffff88017a321c80 task.stack: ffff88017a384000
[    1.047044] RIP: 0010:[<ffffffffb0953ec7>]  [<ffffffffb0953ec7>] usb_detect_quirks+0x88/0xd1

To tackle this odd, let's balance the quirk_count to 0 when the kcalloc
call fails, and defer the quirk setting into a lower level callback
which ensures that the kernel memory management has been initialized.

Fixes: 027bd6cafd9a ("usb: core: Add "quirks" parameter for usbcore")

Signed-off-by: Harry Pan <harry.pan@xxxxxxxxx>
---
 drivers/usb/core/quirks.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/usb/core/quirks.c b/drivers/usb/core/quirks.c
index 097057d2eacf..1fe9843fb9c8 100644
--- a/drivers/usb/core/quirks.c
+++ b/drivers/usb/core/quirks.c
@@ -58,6 +58,7 @@ static int quirks_param_set(const char *val, const struct kernel_param *kp)
 	quirk_list = kcalloc(quirk_count, sizeof(struct quirk_entry),
 			     GFP_KERNEL);
 	if (!quirk_list) {
+		quirk_count = 0;
 		mutex_unlock(&quirk_mutex);
 		return -ENOMEM;
 	}
@@ -154,7 +155,7 @@ static struct kparam_string quirks_param_string = {
 	.string = quirks_param,
 };
 
-module_param_cb(quirks, &quirks_param_ops, &quirks_param_string, 0644);
+device_param_cb(quirks, &quirks_param_ops, &quirks_param_string, 0644);
 MODULE_PARM_DESC(quirks, "Add/modify USB quirks by specifying quirks=vendorID:productID:quirks");
 
 /* Lists of quirky USB devices, split in device quirks and interface quirks.
-- 
2.16.4