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Subject[PATCH] drm/panfrost: Fix GEM handle creation ref-counting
Date
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@chromium.org>
Fixes: f3ba91228e8e ("drm/panfrost: Add initial panfrost driver")
Signed-off-by: Steven Price <steven.price@arm.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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