[PATCH 4.4 132/132] PCI: Fix pci_slot_release() NULL pointer dereference

Greg Kroah-Hartman
2020-12-28T12:58:42Z

From: Jubin Zhong <zhongjubin@huawei.com>

commit 4684709bf81a2d98152ed6b610e3d5c403f9bced upstream.

If kobject_init_and_add() fails, pci_slot_release() is called to delete
slot->list from parent->slots. But slot->list hasn't been initialized
yet, so we dereference a NULL pointer:

Unable to handle kernel NULL pointer dereference at virtual address
00000000
...
CPU: 10 PID: 1 Comm: swapper/0 Not tainted 4.4.240 #197
task: ffffeb398a45ef10 task.stack: ffffeb398a470000
PC is at __list_del_entry_valid+0x5c/0xb0
LR is at pci_slot_release+0x84/0xe4
...
__list_del_entry_valid+0x5c/0xb0
pci_slot_release+0x84/0xe4
kobject_put+0x184/0x1c4
pci_create_slot+0x17c/0x1b4
__pci_hp_initialize+0x68/0xa4
pciehp_probe+0x1a4/0x2fc
pcie_port_probe_service+0x58/0x84
driver_probe_device+0x320/0x470

Initialize slot->list before calling kobject_init_and_add() to avoid this.

Fixes: 8a94644b440e ("PCI: Fix pci_create_slot() reference count leak")
Link: https://lore.kernel.org/r/1606876422-117457-1-git-send-email-zhongjubin@huawei.com
Signed-off-by: Jubin Zhong <zhongjubin@huawei.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Cc: stable@vger.kernel.org # v5.9+
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
drivers/pci/slot.c | 6 +++---
1 file changed, 3 insertions(+), 3 deletions(-)

--- a/drivers/pci/slot.c
+++ b/drivers/pci/slot.c
@@ -307,6 +307,9 @@ placeholder:
goto err;
}

+ INIT_LIST_HEAD(&slot->list);
+ list_add(&slot->list, &parent->slots);
+
err = kobject_init_and_add(&slot->kobj, &pci_slot_ktype, NULL,
"%s", slot_name);
if (err) {
@@ -314,9 +317,6 @@ placeholder:
goto err;
}

- INIT_LIST_HEAD(&slot->list);
- list_add(&slot->list, &parent->slots);
-
down_read(&pci_bus_sem);
list_for_each_entry(dev, &parent->devices, bus_list)
if (PCI_SLOT(dev->devfn) == slot_nr)