Re: [PATCH v3] iommu: Fix potential use-after-free during probe
From: Robin Murphy
Date: Fri Jan 21 2022 - 14:20:56 EST
On 2022-01-21 07:16, Vijayanand Jitta wrote:
On 1/18/2022 9:27 PM, Vijayanand Jitta wrote:
On 1/18/2022 7:19 PM, Robin Murphy wrote:
On 2022-01-12 13:13, Vijayanand Jitta wrote:
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) {
This doesn't seem right - we can't have a non-deterministic situation
where __iommu_probe_device() may or may not be called depending on what
anyone else might be doing with the device at the same time.
I don't fully understand how __iommu_probe_device() and
of_iommu_configure() can be running for the same device at the same
time, but if that's not a race which can be fixed in its own right, then
Thanks for the review comments.
During arm_smmu probe, bus_for_each_dev is called which calls
__iommu_probe_device for each all the devs on that bus.
__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]
and the deferred probe function is calling of_iommu_configure on the
same dev which is currently in __iommu_probe_device path in this case
thus causing the race.
I think adding a refcount to dev_iommu would be a more sensible way to
mitigate it.
Right, Adding refcount for dev_iommu should help , I'll post a new patch
with it.
I was seeing if refcount would help here, there is some issues if we add
a refcount within struct dev_iommu
Here the race between below two functions
process 1:
static void dev_iommu_free(struct device *dev)
{
iommu_fwspec_free(dev);
kfree(dev->iommu);
dev->iommu = NULL;
}
Process 2:
static inline struct iommu_fwspec *dev_iommu_fwspec_get(struct device *dev)
{
if (dev->iommu)
return dev->iommu->fwspec;
else
return NULL;
}
when process1 is in kfree(dev->iommu) , process2 passes the check of
if(dev->iommu) and later get the use after free error when it accesses
dev->iomm->fwspec.
Even if we add a refcount within dev_iommu and then call dev_iommu_free
when refcount reaches 0, we later can't check this refcount in
dev_iommu_fwspec_get since its already freed with kfree.
Another issue is iommu_fwspec_free which is called within dev_iommu_free
calls dev_iommu_fwspec_get , so this again causes issue with refcount.
So, I was thinking of adding something like a bool var iommu_dev_set
with in struct device itself and we initialize during dev_iommu_get and
set it to zero in dev_iommu_free, rest of the places we just check it.
Any thoughts on this ?
Well, yeah... "adding a refcount to dev_iommu" doesn't mean literally
just bodging an extra variable into code not designed for concurrency,
it was meant to imply "thoroughly redesign the current dev_iommu
interfaces to work in a reference-counted manner which actually
acknowledges concurrent usage". The places that currently call
dev_iommu_free() would still set dev->iommu to NULL, *then* drop the
reference from iommu_probe_device(). There wouldn't even need to be an
iommu_fwspec_free() any more, just an iommu_fwspec_put() that releases
the reference from iommu_fwspec_get(), and so on. Having thought it
through this far, though, there are some fiddly bits, and it worries me
that it might be getting too complex for a quick fix, where the real
problem is that the concurrency shouldn't exist in the first place.
Is just bodging dev_iommu_free() into a more sensible order enough to
hide the problem for now? Strictly it might want a memory barrier in
there, but memory ordering is not what I want to be thinking about at
dinnertime on a Friday :)
Robin
----->8-----
diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c
index 8b86406b7162..9d58a515709e 100644
--- a/drivers/iommu/iommu.c
+++ b/drivers/iommu/iommu.c
@@ -207,9 +207,14 @@ static struct dev_iommu *dev_iommu_get(struct
device *dev)
static void dev_iommu_free(struct device *dev)
{
- iommu_fwspec_free(dev);
- kfree(dev->iommu);
+ struct dev_iommu *param = dev->iommu;
+
dev->iommu = NULL;
+ if (param->fwspec) {
+ fwnode_handle_put(param->fwspec->iommu_fwnode);
+ kfree(param->fwspec);
+ }
+ kfree(param);
}
static int __iommu_probe_device(struct device *dev, struct list_head
*group_list)
@@ -2901,13 +2906,7 @@ EXPORT_SYMBOL_GPL(iommu_fwspec_init);
void iommu_fwspec_free(struct device *dev)
{
- struct iommu_fwspec *fwspec = dev_iommu_fwspec_get(dev);
-
- if (fwspec) {
- fwnode_handle_put(fwspec->iommu_fwnode);
- kfree(fwspec);
- dev_iommu_fwspec_set(dev, NULL);
- }
+ /*TODO: dev_iommu made this redundant */
}
EXPORT_SYMBOL_GPL(iommu_fwspec_free);