[PATCH v3] iommu: Fix potential use-after-free during probe

[Vijayanand]

From: Vijayanand Jitta <quic_vjitta@xxxxxxxxxxx>

Kasan has reported the following use after free on dev->iommu.
when a device probe fails and it is in process of freeing dev->iommu
in dev_iommu_free function, a deferred_probe_work_func runs in parallel
and tries to access dev->iommu->fwspec in of_iommu_configure path thus
causing use after free.

BUG: KASAN: use-after-free in of_iommu_configure+0xb4/0x4a4
Read of size 8 at addr ffffff87a2f1acb8 by task kworker/u16:2/153

Workqueue: events_unbound deferred_probe_work_func
Call trace:
 dump_backtrace+0x0/0x33c
 show_stack+0x18/0x24
 dump_stack_lvl+0x16c/0x1e0
 print_address_description+0x84/0x39c
 __kasan_report+0x184/0x308
 kasan_report+0x50/0x78
 __asan_load8+0xc0/0xc4
 of_iommu_configure+0xb4/0x4a4
 of_dma_configure_id+0x2fc/0x4d4
 platform_dma_configure+0x40/0x5c
 really_probe+0x1b4/0xb74
 driver_probe_device+0x11c/0x228
 __device_attach_driver+0x14c/0x304
 bus_for_each_drv+0x124/0x1b0
 __device_attach+0x25c/0x334
 device_initial_probe+0x24/0x34
 bus_probe_device+0x78/0x134
 deferred_probe_work_func+0x130/0x1a8
 process_one_work+0x4c8/0x970
 worker_thread+0x5c8/0xaec
 kthread+0x1f8/0x220
 ret_from_fork+0x10/0x18

Allocated by task 1:
 ____kasan_kmalloc+0xd4/0x114
 __kasan_kmalloc+0x10/0x1c
 kmem_cache_alloc_trace+0xe4/0x3d4
 __iommu_probe_device+0x90/0x394
 probe_iommu_group+0x70/0x9c
 bus_for_each_dev+0x11c/0x19c
 bus_iommu_probe+0xb8/0x7d4
 bus_set_iommu+0xcc/0x13c
 arm_smmu_bus_init+0x44/0x130 [arm_smmu]
 arm_smmu_device_probe+0xb88/0xc54 [arm_smmu]
 platform_drv_probe+0xe4/0x13c
 really_probe+0x2c8/0xb74
 driver_probe_device+0x11c/0x228
 device_driver_attach+0xf0/0x16c
 __driver_attach+0x80/0x320
 bus_for_each_dev+0x11c/0x19c
 driver_attach+0x38/0x48
 bus_add_driver+0x1dc/0x3a4
 driver_register+0x18c/0x244
 __platform_driver_register+0x88/0x9c
 init_module+0x64/0xff4 [arm_smmu]
 do_one_initcall+0x17c/0x2f0
 do_init_module+0xe8/0x378
 load_module+0x3f80/0x4a40
 __se_sys_finit_module+0x1a0/0x1e4
 __arm64_sys_finit_module+0x44/0x58
 el0_svc_common+0x100/0x264
 do_el0_svc+0x38/0xa4
 el0_svc+0x20/0x30
 el0_sync_handler+0x68/0xac
 el0_sync+0x160/0x180

Freed by task 1:
 kasan_set_track+0x4c/0x84
 kasan_set_free_info+0x28/0x4c
 ____kasan_slab_free+0x120/0x15c
 __kasan_slab_free+0x18/0x28
 slab_free_freelist_hook+0x204/0x2fc
 kfree+0xfc/0x3a4
 __iommu_probe_device+0x284/0x394
 probe_iommu_group+0x70/0x9c
 bus_for_each_dev+0x11c/0x19c
 bus_iommu_probe+0xb8/0x7d4
 bus_set_iommu+0xcc/0x13c
 arm_smmu_bus_init+0x44/0x130 [arm_smmu]
 arm_smmu_device_probe+0xb88/0xc54 [arm_smmu]
 platform_drv_probe+0xe4/0x13c
 really_probe+0x2c8/0xb74
 driver_probe_device+0x11c/0x228
 device_driver_attach+0xf0/0x16c
 __driver_attach+0x80/0x320
 bus_for_each_dev+0x11c/0x19c
 driver_attach+0x38/0x48
 bus_add_driver+0x1dc/0x3a4
 driver_register+0x18c/0x244
 __platform_driver_register+0x88/0x9c
 init_module+0x64/0xff4 [arm_smmu]
 do_one_initcall+0x17c/0x2f0
 do_init_module+0xe8/0x378
 load_module+0x3f80/0x4a40
 __se_sys_finit_module+0x1a0/0x1e4
 __arm64_sys_finit_module+0x44/0x58
 el0_svc_common+0x100/0x264
 do_el0_svc+0x38/0xa4
 el0_svc+0x20/0x30
 el0_sync_handler+0x68/0xac
 el0_sync+0x160/0x180

Fix this by taking device_lock during probe_iommu_group.

Signed-off-by: Vijayanand Jitta <quic_vjitta@xxxxxxxxxxx>
---
 drivers/iommu/iommu.c | 12 ++++++++----
 1 file changed, 8 insertions(+), 4 deletions(-)

diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c
index dd7863e..261792d 100644
--- a/drivers/iommu/iommu.c
+++ b/drivers/iommu/iommu.c
@@ -1617,7 +1617,7 @@ static int probe_iommu_group(struct device *dev, void *data)
 {
 	struct list_head *group_list = data;
 	struct iommu_group *group;
-	int ret;
+	int ret = 0;
 
 	/* Device is probed already if in a group */
 	group = iommu_group_get(dev);
@@ -1626,9 +1626,13 @@ static int probe_iommu_group(struct device *dev, void *data)
 		return 0;
 	}
 
-	ret = __iommu_probe_device(dev, group_list);
-	if (ret == -ENODEV)
-		ret = 0;
+	ret = device_trylock(dev);
+	if (ret) {
+		ret = __iommu_probe_device(dev, group_list);
+		if (ret == -ENODEV)
+			ret = 0;
+		device_unlock(dev);
+	}
 
 	return ret;
 }
-- 
2.7.4