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drm/msm: protect against faults from copy_from_user() in submit ioctl 

An evil userspace could try to cause deadlock by passing an unfaulted-in
GEM bo as submit->bos (or submit->cmds) table.  Which will trigger
msm_gem_fault() while we already hold struct_mutex.  See:

https://github.com/freedreno/msmtest/blob/master/evilsubmittest.c

Cc: stable@vger.kernel.org
Signed-off-by: Rob Clark <robdclark@gmail.com>
This commit is contained in:
Rob Clark 2016-08-22 15:28:38 -04:00
parent 89f82cbb0d
commit d78d383ab3
3 changed files with 18 additions and 0 deletions
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6
drivers/gpu/drm/msm/msm_drv.h
View File

@ -157,6 +157,12 @@ struct msm_drm_private {
struct shrinker shrinker;
struct msm_vblank_ctrl vblank_ctrl;
/* task holding struct_mutex.. currently only used in submit path
* to detect and reject faults from copy_from_user() for submit
* ioctl.
*/
struct task_struct *struct_mutex_task;
};
struct msm_format {

9
drivers/gpu/drm/msm/msm_gem.c
View File

@ -196,11 +196,20 @@ int msm_gem_fault(struct vm_area_struct *vma, struct vm_fault *vmf)
{
struct drm_gem_object *obj = vma->vm_private_data;
struct drm_device *dev = obj->dev;
struct msm_drm_private *priv = dev->dev_private;
struct page **pages;
unsigned long pfn;
pgoff_t pgoff;
int ret;
/* This should only happen if userspace tries to pass a mmap'd
* but unfaulted gem bo vaddr into submit ioctl, triggering
* a page fault while struct_mutex is already held. This is
* not a valid use-case so just bail.
*/
if (priv->struct_mutex_task == current)
return VM_FAULT_SIGBUS;
/* Make sure we don't parallel update on a fault, nor move or remove
* something from beneath our feet
*/

3
drivers/gpu/drm/msm/msm_gem_submit.c
View File

@ -394,6 +394,8 @@ int msm_ioctl_gem_submit(struct drm_device *dev, void *data,
if (ret)
return ret;
priv->struct_mutex_task = current;
submit = submit_create(dev, gpu, args->nr_bos, args->nr_cmds);
if (!submit) {
ret = -ENOMEM;
@ -485,6 +487,7 @@ out:
if (ret)
msm_gem_submit_free(submit);
out_unlock:
priv->struct_mutex_task = NULL;
mutex_unlock(&dev->struct_mutex);
return ret;
}