Fix EPF configfs attribute group removal

A couple of patches to fix removal of configfs attribute groups of a PCI endpoint function driver.

Changes from v2:
- Use list_del() instead of list_del_init() in patch 2
- Added Niklas' review tags

Changes from v1:
- Split out patch 1 from patch 2 as requested by Niklas.

Damien Le Moal (2):
PCI: endpoint: Fix configfs group list head handling
PCI: endpoint: Fix configfs group removal on driver teardown

 drivers/pci/endpoint/pci-ep-cfs.c   | 1 +
 drivers/pci/endpoint/pci-epf-core.c | 2 +-
 2 files changed, 2 insertions(+), 1 deletion(-)

2.49.0

Doing a list_del() on the epf_group field of struct pci_epf_driver in pci_epf_remove_cfs() is not correct as this field is a list head, not a list entry. This list_del() call triggers a KASAN warning when an endpoint function driver which has a configfs attribute group is torn down:

==================================================================

BUG: KASAN: slab-use-after-free in pci_epf_remove_cfs+0x17c/0x198
Write of size 8 at addr ffff00010f4a0d80 by task rmmod/319

CPU: 3 UID: 0 PID: 319 Comm: rmmod Not tainted 6.16.0-rc2 #1 NONE
Hardware name: Radxa ROCK 5B (DT)
Call trace:
show_stack+0x2c/0x84 (C)
dump_stack_lvl+0x70/0x98
print_report+0x17c/0x538
kasan_report+0xb8/0x190
__asan_report_store8_noabort+0x20/0x2c
pci_epf_remove_cfs+0x17c/0x198
pci_epf_unregister_driver+0x18/0x30
nvmet_pci_epf_cleanup_module+0x24/0x30 [nvmet_pci_epf]
__arm64_sys_delete_module+0x264/0x424
invoke_syscall+0x70/0x260
el0_svc_common.constprop.0+0xac/0x230
do_el0_svc+0x40/0x58
el0_svc+0x48/0xdc
el0t_64_sync_handler+0x10c/0x138
el0t_64_sync+0x198/0x19c

...

Remove this incorrect list_del() call from pci_epf_remove_cfs().

---
 drivers/pci/endpoint/pci-epf-core.c | 1 -
 1 file changed, 1 deletion(-)

index 577a9e490115..defc6aecfdef 100644
@@ -338,7 +338,6 @@ static void pci_epf_remove_cfs(struct pci_epf_driver *driver)
 	mutex_lock(&pci_epf_mutex);
 	list_for_each_entry_safe(group, tmp, &driver->epf_group, group_entry)
 		pci_ep_cfs_remove_epf_group(group);
-	list_del(&driver->epf_group);
 	mutex_unlock(&pci_epf_mutex);
 }
 

2.49.0

An endpoint driver configfs attributes group is added to the epf_group list of struct pci_epf_driver by pci_epf_add_cfs() but an added group is not removed from this list when the attribute group is unregistered with pci_ep_cfs_remove_epf_group().

Add the missing list_del() call in pci_ep_cfs_remove_epf_group() to correctly remove the attribute group from the driver list.

With this change, once the loop over all attribute groups in pci_epf_remove_cfs() completes, the driver epf_group list should be empty. Add a WARN_ON() to make sure of that.

---
 drivers/pci/endpoint/pci-ep-cfs.c   | 1 +
 drivers/pci/endpoint/pci-epf-core.c | 1 +
 2 files changed, 2 insertions(+)

index d712c7a866d2..ef50c82e647f 100644
@@ -691,6 +691,7 @@ void pci_ep_cfs_remove_epf_group(struct config_group *group)
 	if (IS_ERR_OR_NULL(group))
 		return;
 
+	list_del(&group->group_entry);
 	configfs_unregister_default_group(group);
 }
 EXPORT_SYMBOL(pci_ep_cfs_remove_epf_group);

index defc6aecfdef..167dc6ee63f7 100644
@@ -338,6 +338,7 @@ static void pci_epf_remove_cfs(struct pci_epf_driver *driver)
 	mutex_lock(&pci_epf_mutex);
 	list_for_each_entry_safe(group, tmp, &driver->epf_group, group_entry)
 		pci_ep_cfs_remove_epf_group(group);
+	WARN_ON(!list_empty(&driver->epf_group));
 	mutex_unlock(&pci_epf_mutex);
 }
 

2.49.0

Applied, thanks!

[1/2] PCI: endpoint: Fix configfs group list head handling

      commit: d79123d79a8154b4318529b7b2ff7e15806f480b
[2/2] PCI: endpoint: Fix configfs group removal on driver teardown
      commit: 910bdb8197f9322790c738bb32feaa11dba26909

Best regards,

Manivannan Sadhasivam <[email protected]>