commit 11a1f4bc47362700fcbde717292158873fb847ed upstream.

Keith reports a use-after-free when a DPC event occurs concurrently to hot-removal of the same portion of the hierarchy:

The dpc_handler() awaits readiness of the secondary bus below the Downstream Port where the DPC event occurred. To do so, it polls the config space of the first child device on the secondary bus. If that child device is concurrently removed, accesses to its struct pci_dev cause the kernel to oops.

That's because pci_bridge_wait_for_secondary_bus() neglects to hold a reference on the child device. Before v6.3, the function was only called on resume from system sleep or on runtime resume. Holding a reference wasn't necessary back then because the pciehp IRQ thread could never run concurrently. (On resume from system sleep, IRQs are not enabled until after the resume_noirq phase. And runtime resume is always awaited before a PCI device is removed.)

However starting with v6.3, pci_bridge_wait_for_secondary_bus() is also called on a DPC event. Commit 53b54ad074de ("PCI/DPC: Await readiness of secondary bus after reset"), which introduced that, failed to appreciate that pci_bridge_wait_for_secondary_bus() now needs to hold a reference on the child device because dpc_handler() and pciehp may indeed run concurrently. The commit was backported to v5.10+ stable kernels, so that's the oldest one affected.

Add the missing reference acquisition.

Abridged stack trace:

BUG: unable to handle page fault for address: 00000000091400c0 CPU: 15 PID: 2464 Comm: irq/53-pcie-dpc 6.9.0 RIP: pci_bus_read_config_dword+0x17/0x50 pci_dev_wait() pci_bridge_wait_for_secondary_bus() dpc_reset_link() pcie_do_recovery() dpc_handler()

Fixes: 53b54ad074de ("PCI/DPC: Await readiness of secondary bus after reset") Closes: https://lore.kernel.org/r/20240612181625.3604512-3-kbusch@meta.com/ Link: https://lore.kernel.org/linux-pci/8e4bcd4116fd94f592f2bf2749f168099c480ddf.1... Reported-by: Keith Busch kbusch@kernel.org Tested-by: Keith Busch kbusch@kernel.org Signed-off-by: Lukas Wunner lukas@wunner.de Signed-off-by: Krzysztof Wilczyński kwilczynski@kernel.org Reviewed-by: Keith Busch kbusch@kernel.org Reviewed-by: Mika Westerberg mika.westerberg@linux.intel.com Cc: stable@vger.kernel.org # v5.10+ --- drivers/pci/pci.c | 19 ++++++++++++------- 1 file changed, 12 insertions(+), 7 deletions(-)

diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c index 530ced8f7abd..09d5fa637b98 100644 --- a/drivers/pci/pci.c +++ b/drivers/pci/pci.c @@ -4817,7 +4817,7 @@ int pci_bridge_wait_for_secondary_bus(struct pci_dev *dev, char *reset_type, int timeout) { struct pci_dev *child; - int delay; + int delay, ret = 0;

if (pci_dev_is_disconnected(dev)) return 0; @@ -4845,8 +4845,8 @@ int pci_bridge_wait_for_secondary_bus(struct pci_dev *dev, char *reset_type, return 0; }

- child = list_first_entry(&dev->subordinate->devices, struct pci_dev, - bus_list); + child = pci_dev_get(list_first_entry(&dev->subordinate->devices, + struct pci_dev, bus_list)); up_read(&pci_bus_sem);

/* @@ -4856,7 +4856,7 @@ int pci_bridge_wait_for_secondary_bus(struct pci_dev *dev, char *reset_type, if (!pci_is_pcie(dev)) { pci_dbg(dev, "waiting %d ms for secondary bus\n", 1000 + delay); msleep(1000 + delay); - return 0; + goto put_child; }

/* @@ -4877,7 +4877,7 @@ int pci_bridge_wait_for_secondary_bus(struct pci_dev *dev, char *reset_type, * until the timeout expires. */ if (!pcie_downstream_port(dev)) - return 0; + goto put_child;

if (pcie_get_speed_cap(dev) <= PCIE_SPEED_5_0GT) { pci_dbg(dev, "waiting %d ms for downstream link\n", delay); @@ -4888,11 +4888,16 @@ int pci_bridge_wait_for_secondary_bus(struct pci_dev *dev, char *reset_type, if (!pcie_wait_for_link_delay(dev, true, delay)) { /* Did not train, no need to wait any further */ pci_info(dev, "Data Link Layer Link Active not set in 1000 msec\n"); - return -ENOTTY; + ret = -ENOTTY; + goto put_child; } }

- return pci_dev_wait(child, reset_type, timeout - delay); + ret = pci_dev_wait(child, reset_type, timeout - delay); + +put_child: + pci_dev_put(child); + return ret; }

void pci_reset_secondary_bus(struct pci_dev *dev)