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Date: Wed, 21 Dec 2022 15:11:09 +0000
From: Steven Price <steven.price@....com>
To: Rob Clark <robdclark@...il.com>
Cc: Rob Herring <robh@...nel.org>,
Tomeu Vizoso <tomeu.vizoso@...labora.com>,
Alyssa Rosenzweig <alyssa.rosenzweig@...labora.com>,
Rob Clark <robdclark@...omium.org>,
linux-kernel@...r.kernel.org, dri-devel@...ts.freedesktop.org
Subject: Re: [PATCH] drm/panfrost: Fix GEM handle creation ref-counting
On 19/12/2022 17:10, Rob Clark wrote:
> On Mon, Dec 19, 2022 at 6:02 AM Steven Price <steven.price@....com> wrote:
>>
>> panfrost_gem_create_with_handle() previously returned a BO but with the
>> only reference being from the handle, which user space could in theory
>> guess and release, causing a use-after-free. Additionally if the call to
>> panfrost_gem_mapping_get() in panfrost_ioctl_create_bo() failed then
>> a(nother) reference on the BO was dropped.
>>
>> The _create_with_handle() is a problematic pattern, so ditch it and
>> instead create the handle in panfrost_ioctl_create_bo(). If the call to
>> panfrost_gem_mapping_get() fails then this means that user space has
>> indeed gone behind our back and freed the handle. In which case just
>> return an error code.
>>
>> Reported-by: Rob Clark <robdclark@...omium.org>
>
> Yeah, I like getting rid of the _create_with_handle() pattern, the
> only place where that pattern works is if you immediately return the
> handle to userspace (and don't otherwise touch the obj)
>
> Reviewed-by: Rob Clark <robdclark@...il.com>
Thanks, I've pushed this to drm-misc-fixes:
4217c6ac8174 ("drm/panfrost: Fix GEM handle creation ref-counting")
Steve
>> Fixes: f3ba91228e8e ("drm/panfrost: Add initial panfrost driver")
>> Signed-off-by: Steven Price <steven.price@....com>
>> ---
>> drivers/gpu/drm/panfrost/panfrost_drv.c | 27 ++++++++++++++++---------
>> drivers/gpu/drm/panfrost/panfrost_gem.c | 16 +--------------
>> drivers/gpu/drm/panfrost/panfrost_gem.h | 5 +----
>> 3 files changed, 20 insertions(+), 28 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/panfrost/panfrost_drv.c b/drivers/gpu/drm/panfrost/panfrost_drv.c
>> index fa619fe72086..abb0dadd8f63 100644
>> --- a/drivers/gpu/drm/panfrost/panfrost_drv.c
>> +++ b/drivers/gpu/drm/panfrost/panfrost_drv.c
>> @@ -82,6 +82,7 @@ static int panfrost_ioctl_create_bo(struct drm_device *dev, void *data,
>> struct panfrost_gem_object *bo;
>> struct drm_panfrost_create_bo *args = data;
>> struct panfrost_gem_mapping *mapping;
>> + int ret;
>>
>> if (!args->size || args->pad ||
>> (args->flags & ~(PANFROST_BO_NOEXEC | PANFROST_BO_HEAP)))
>> @@ -92,21 +93,29 @@ static int panfrost_ioctl_create_bo(struct drm_device *dev, void *data,
>> !(args->flags & PANFROST_BO_NOEXEC))
>> return -EINVAL;
>>
>> - bo = panfrost_gem_create_with_handle(file, dev, args->size, args->flags,
>> - &args->handle);
>> + bo = panfrost_gem_create(dev, args->size, args->flags);
>> if (IS_ERR(bo))
>> return PTR_ERR(bo);
>>
>> + ret = drm_gem_handle_create(file, &bo->base.base, &args->handle);
>> + if (ret)
>> + goto out;
>> +
>> mapping = panfrost_gem_mapping_get(bo, priv);
>> - if (!mapping) {
>> - drm_gem_object_put(&bo->base.base);
>> - return -EINVAL;
>> + if (mapping) {
>> + args->offset = mapping->mmnode.start << PAGE_SHIFT;
>> + panfrost_gem_mapping_put(mapping);
>> + } else {
>> + /* This can only happen if the handle from
>> + * drm_gem_handle_create() has already been guessed and freed
>> + * by user space
>> + */
>> + ret = -EINVAL;
>> }
>>
>> - args->offset = mapping->mmnode.start << PAGE_SHIFT;
>> - panfrost_gem_mapping_put(mapping);
>> -
>> - return 0;
>> +out:
>> + drm_gem_object_put(&bo->base.base);
>> + return ret;
>> }
>>
>> /**
>> diff --git a/drivers/gpu/drm/panfrost/panfrost_gem.c b/drivers/gpu/drm/panfrost/panfrost_gem.c
>> index 293e799e2fe8..3c812fbd126f 100644
>> --- a/drivers/gpu/drm/panfrost/panfrost_gem.c
>> +++ b/drivers/gpu/drm/panfrost/panfrost_gem.c
>> @@ -235,12 +235,8 @@ struct drm_gem_object *panfrost_gem_create_object(struct drm_device *dev, size_t
>> }
>>
>> struct panfrost_gem_object *
>> -panfrost_gem_create_with_handle(struct drm_file *file_priv,
>> - struct drm_device *dev, size_t size,
>> - u32 flags,
>> - uint32_t *handle)
>> +panfrost_gem_create(struct drm_device *dev, size_t size, u32 flags)
>> {
>> - int ret;
>> struct drm_gem_shmem_object *shmem;
>> struct panfrost_gem_object *bo;
>>
>> @@ -256,16 +252,6 @@ panfrost_gem_create_with_handle(struct drm_file *file_priv,
>> bo->noexec = !!(flags & PANFROST_BO_NOEXEC);
>> bo->is_heap = !!(flags & PANFROST_BO_HEAP);
>>
>> - /*
>> - * Allocate an id of idr table where the obj is registered
>> - * and handle has the id what user can see.
>> - */
>> - ret = drm_gem_handle_create(file_priv, &shmem->base, handle);
>> - /* drop reference from allocate - handle holds it now. */
>> - drm_gem_object_put(&shmem->base);
>> - if (ret)
>> - return ERR_PTR(ret);
>> -
>> return bo;
>> }
>>
>> diff --git a/drivers/gpu/drm/panfrost/panfrost_gem.h b/drivers/gpu/drm/panfrost/panfrost_gem.h
>> index 8088d5fd8480..ad2877eeeccd 100644
>> --- a/drivers/gpu/drm/panfrost/panfrost_gem.h
>> +++ b/drivers/gpu/drm/panfrost/panfrost_gem.h
>> @@ -69,10 +69,7 @@ panfrost_gem_prime_import_sg_table(struct drm_device *dev,
>> struct sg_table *sgt);
>>
>> struct panfrost_gem_object *
>> -panfrost_gem_create_with_handle(struct drm_file *file_priv,
>> - struct drm_device *dev, size_t size,
>> - u32 flags,
>> - uint32_t *handle);
>> +panfrost_gem_create(struct drm_device *dev, size_t size, u32 flags);
>>
>> int panfrost_gem_open(struct drm_gem_object *obj, struct drm_file *file_priv);
>> void panfrost_gem_close(struct drm_gem_object *obj,
>> --
>> 2.34.1
>>
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