Re: [PATCH] drm/panthor: Prevent potential UAF in group creation

[Boris Brezillon <boris.brezillon@collabora.com>]

On Thu, 27 Nov 2025 16:02:15 +0000
Steven Price <steven.price@arm.com> wrote:

> On 27/11/2025 08:12, Akash Goel wrote:
> > This commit prevents the possibility of a use after free issue in the
> > GROUP_CREATE ioctl function, which arose as pointer to the group is
> > accessed in that ioctl function after storing it in the Xarray.
> > A malicious userspace can second guess the handle of a group and try
> > to call GROUP_DESTROY ioctl from another thread around the same time
> > as GROUP_CREATE ioctl.
> > 
> > To prevent the use after free exploit, this commit uses a mark on an
> > entry of group pool Xarray which is added just before returning from
> > the GROUP_CREATE ioctl function. The mark is checked for all ioctls
> > that specify the group handle and so userspace won't be abe to delete
> > a group that isn't marked yet.
> > 
> > Co-developed-by: Boris Brezillon <boris.brezillon@collabora.com>
> > Signed-off-by: Akash Goel <akash.goel@arm.com>  
> 
> Reviewed-by: Steven Price <steven.price@arm.com>
> 
> I *think* this should have a...
> 
> Fixes: d2624d90a0b7 ("drm/panthor: assign unique names to queues")
> 
> ... as I don't believe it was a problem before the rearrangement that
> happened there.

Oh, yeah, I didn't notice the commit was missing a Fixes tag, and
you're correct about the offending commit.

> 
> Thanks,
> Steve
> 
> > ---
> >  drivers/gpu/drm/panthor/panthor_sched.c | 19 +++++++++++++++----
> >  1 file changed, 15 insertions(+), 4 deletions(-)
> > 
> > diff --git a/drivers/gpu/drm/panthor/panthor_sched.c b/drivers/gpu/drm/panthor/panthor_sched.c
> > index b834123a6560..a6b8024e1a3c 100644
> > --- a/drivers/gpu/drm/panthor/panthor_sched.c
> > +++ b/drivers/gpu/drm/panthor/panthor_sched.c
> > @@ -779,6 +779,12 @@ struct panthor_job_profiling_data {
> >   */
> >  #define MAX_GROUPS_PER_POOL 128
> >  
> > +/*
> > + * Mark added on an entry of group pool Xarray to identify if the group has
> > + * been fully initialized and can be accessed elsewhere in the driver code.
> > + */
> > +#define GROUP_REGISTERED XA_MARK_1
> > +
> >  /**
> >   * struct panthor_group_pool - Group pool
> >   *
> > @@ -3007,7 +3013,7 @@ void panthor_fdinfo_gather_group_samples(struct panthor_file *pfile)
> >  		return;
> >  
> >  	xa_lock(&gpool->xa);
> > -	xa_for_each(&gpool->xa, i, group) {
> > +	xa_for_each_marked(&gpool->xa, i, group, GROUP_REGISTERED) {
> >  		guard(spinlock)(&group->fdinfo.lock);
> >  		pfile->stats.cycles += group->fdinfo.data.cycles;
> >  		pfile->stats.time += group->fdinfo.data.time;
> > @@ -3727,6 +3733,8 @@ int panthor_group_create(struct panthor_file *pfile,
> >  
> >  	group_init_task_info(group);
> >  
> > +	xa_set_mark(&gpool->xa, gid, GROUP_REGISTERED);
> > +
> >  	return gid;
> >  
> >  err_erase_gid:
> > @@ -3744,6 +3752,9 @@ int panthor_group_destroy(struct panthor_file *pfile, u32 group_handle)
> >  	struct panthor_scheduler *sched = ptdev->scheduler;
> >  	struct panthor_group *group;
> >  
> > +	if (!xa_get_mark(&gpool->xa, group_handle, GROUP_REGISTERED))
> > +		return -EINVAL;
> > +
> >  	group = xa_erase(&gpool->xa, group_handle);
> >  	if (!group)
> >  		return -EINVAL;
> > @@ -3769,12 +3780,12 @@ int panthor_group_destroy(struct panthor_file *pfile, u32 group_handle)
> >  }
> >  
> >  static struct panthor_group *group_from_handle(struct panthor_group_pool *pool,
> > -					       u32 group_handle)
> > +					       unsigned long group_handle)
> >  {
> >  	struct panthor_group *group;
> >  
> >  	xa_lock(&pool->xa);
> > -	group = group_get(xa_load(&pool->xa, group_handle));
> > +	group = group_get(xa_find(&pool->xa, &group_handle, group_handle, GROUP_REGISTERED));
> >  	xa_unlock(&pool->xa);
> >  
> >  	return group;
> > @@ -3861,7 +3872,7 @@ panthor_fdinfo_gather_group_mem_info(struct panthor_file *pfile,
> >  		return;
> >  
> >  	xa_lock(&gpool->xa);
> > -	xa_for_each(&gpool->xa, i, group) {
> > +	xa_for_each_marked(&gpool->xa, i, group, GROUP_REGISTERED) {
> >  		stats->resident += group->fdinfo.kbo_sizes;
> >  		if (group->csg_id >= 0)
> >  			stats->active += group->fdinfo.kbo_sizes;  
>