Re: [PATCH] misc: sgi-gru: fix use-after-free error in gru_set_context_option, gru_fault and gru_handle_user_call_os

[Zheng Hacker]

Hi greg,

I've received your advice and rewrite the patch.

Greg KH <gregkh@xxxxxxxxxxxxxxxxxxx> 于2022年9月16日周五 16:15写道：
>
> On Fri, Sep 16, 2022 at 03:39:57PM +0800, xmzyshypnc wrote:
> > in drivers/misc/sgi-gru/grufile.c, gru_file_unlocked_ioctl function can be called by user. If the req is GRU_SET_CONTEXT_OPTION, it will call gru_set_context_option.
>
> Please properly wrap your changelog text at 72 columns like your editor
> asked you to when you wrote the changelog text.
>
> >
> > In gru_set_context_option, as req can be controlled by user (copy_from_user(&req, (void __user *)arg, sizeof(req))), we can get into sco_blade_chiplet case and reach gru_check_context_placement function call.
> >
> > in gru_check_context_placement function, if the error path was steped, say gru_check_chiplet_assignment return 0, then it will fall into gru_unload_context function,which will call gru_free_gru_context->gts_drop. As gts->ts_refcnt was set to 1 in gru_alloc_gts. It will finnaly call kfree(gts) in gts_drop function.
> >
> > Then gru_unlock_gts will be called in gru_set_context_option function. which is a typical Use after free.
> >
> > The same problem exists in gru_handle_user_call_os function and gru_fault function.
> >
> > Fix it by introduce the return value to see if gts is in good case or not. Free the gts in caller when gru_check_chiplet_assignment check failed.
> >
> > Signed-off-by: xmzyshypnc <1002992920@xxxxxx>
> > ---
> >  drivers/misc/sgi-gru/grufault.c  | 14 ++++++++++++--
> >  drivers/misc/sgi-gru/grumain.c   | 19 +++++++++++++++----
> >  drivers/misc/sgi-gru/grutables.h |  2 +-
> >  3 files changed, 28 insertions(+), 7 deletions(-)
> >
> > diff --git a/drivers/misc/sgi-gru/grufault.c b/drivers/misc/sgi-gru/grufault.c
> > index d7ef61e602ed..08e837a45ad7 100644
> > --- a/drivers/misc/sgi-gru/grufault.c
> > +++ b/drivers/misc/sgi-gru/grufault.c
> > @@ -656,7 +656,13 @@ int gru_handle_user_call_os(unsigned long cb)
> >       if (ucbnum >= gts->ts_cbr_au_count * GRU_CBR_AU_SIZE)
> >               goto exit;
> >
> > -     gru_check_context_placement(gts);
> > +     ret = gru_check_context_placement(gts);
> > +
> > +     if (ret) {
>
> No blank line needed.

Got it.

>
> > +             gru_unlock_gts(gts);
> > +             gru_unload_context(gts, 1);
> > +             return -EINVAL;
>
> Jump to an error block at the end of the function instead?
>
> > +     }
> >
> >       /*
> >        * CCH may contain stale data if ts_force_cch_reload is set.
> > @@ -874,7 +880,7 @@ int gru_set_context_option(unsigned long arg)
> >               } else {
> >                       gts->ts_user_blade_id = req.val1;
> >                       gts->ts_user_chiplet_id = req.val0;
> > -                     gru_check_context_placement(gts);
> > +                     ret = gru_check_context_placement(gts);
> >               }
> >               break;
> >       case sco_gseg_owner:
> > @@ -889,6 +895,10 @@ int gru_set_context_option(unsigned long arg)
> >               ret = -EINVAL;
> >       }
> >       gru_unlock_gts(gts);
> > +     if (ret) {
> > +             gru_unload_context(gts, 1);
> > +             ret = -EINVAL;
> > +     }
> >
> >       return ret;
> >  }
> > diff --git a/drivers/misc/sgi-gru/grumain.c b/drivers/misc/sgi-gru/grumain.c
> > index 9afda47efbf2..e1ecf86df3c1 100644
> > --- a/drivers/misc/sgi-gru/grumain.c
> > +++ b/drivers/misc/sgi-gru/grumain.c
> > @@ -716,9 +716,10 @@ static int gru_check_chiplet_assignment(struct gru_state *gru,
> >   * chiplet. Misassignment can occur if the process migrates to a different
> >   * blade or if the user changes the selected blade/chiplet.
> >   */
> > -void gru_check_context_placement(struct gru_thread_state *gts)
> > +int gru_check_context_placement(struct gru_thread_state *gts)
> >  {
> >       struct gru_state *gru;
> > +     int ret = 0;
> >
> >       /*
> >        * If the current task is the context owner, verify that the
> > @@ -727,14 +728,16 @@ void gru_check_context_placement(struct gru_thread_state *gts)
> >        */
> >       gru = gts->ts_gru;
> >       if (!gru || gts->ts_tgid_owner != current->tgid)
> > -             return;
> > +             return ret;
>
> Why is this succeeding if there was an error?
>

The logic code here is when gts->ts_gru is null, it try again. It
won't free the gts so I think it can still be called after this
branch.

> >
> >       if (!gru_check_chiplet_assignment(gru, gts)) {
> >               STAT(check_context_unload);
> > -             gru_unload_context(gts, 1);
> > +             ret = 1;
>
> 1 is not a valid error value;
>
>
> >       } else if (gru_retarget_intr(gts)) {
> >               STAT(check_context_retarget_intr);
> >       }
> > +
> > +     return ret;
> >  }
> >
> >
> > @@ -919,6 +922,7 @@ vm_fault_t gru_fault(struct vm_fault *vmf)
> >       struct gru_thread_state *gts;
> >       unsigned long paddr, vaddr;
> >       unsigned long expires;
> > +     int ret;
> >
> >       vaddr = vmf->address;
> >       gru_dbg(grudev, "vma %p, vaddr 0x%lx (0x%lx)\n",
> > @@ -934,7 +938,12 @@ vm_fault_t gru_fault(struct vm_fault *vmf)
> >       mutex_lock(&gts->ts_ctxlock);
> >       preempt_disable();
> >
> > -     gru_check_context_placement(gts);
> > +     ret = gru_check_context_placement(gts);
> > +     if (ret) {
> > +             mutex_unlock(&gts->ts_ctxlock);
> > +             gru_unload_context(gts, 1);
> > +             return VM_FAULT_NOPAGE;
>
> Why not return ret?
>

Got it.

> > +     }
> >
> >       if (!gts->ts_gru) {
> >               STAT(load_user_context);
> > @@ -958,6 +967,8 @@ vm_fault_t gru_fault(struct vm_fault *vmf)
> >       preempt_enable();
> >       mutex_unlock(&gts->ts_ctxlock);
> >
> > +
> > +
>
> Why the blank lines added?
>

Removed.

Best regards,

Zheng Wang