Messages in this thread Patch in this message | | | Date | Fri, 21 Jan 2022 19:20:30 +0000 | Subject | Re: [PATCH v3] iommu: Fix potential use-after-free during probe | From | Robin Murphy <> |
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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@quicinc.com> >>>> --- >>>> 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);
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