Re: [PATCH v4] misc: sgi-gru: fix use-after-free error in gru_set_context_option, gru_fault and gru_handle_user_call_os

From: Zheng Hacker
Date: Wed Oct 26 2022 - 22:53:58 EST

Hi Dimitri Sivanich,

Sorry for my late reply. I was a little busy last week. I'll check the
code right now and let you know.

Thanks for your suggestion :)

Best Regards,
Zheng Wang

Dimitri Sivanich <sivanich@xxxxxxx> 于2022年10月19日周三 22:00写道：
>
> On Wed, Oct 19, 2022 at 11:14:45AM +0800, Zheng Wang wrote:
> > Gts may be freed in gru_check_chiplet_assignment.
> > The caller still use it after that, UAF happens.
> >
> > Fix it by introducing a return value to see if it's in error path or not.
> > Free the gts in caller if gru_check_chiplet_assignment check failed.
> >
> > Fixes: 55484c45dbec ("gru: allow users to specify gru chiplet 2")
> > Reported-by: Zheng Wang <hackerzheng666@xxxxxxxxx>
> > Signed-off-by: Zheng Wang <zyytlz.wz@xxxxxxx>
> > ---
> > v4:
> > - use VM_FAULT_NOPAGE as failure code in gru_fault and -EINVAL in other functions suggested by Yejian
> >
> > v3:
> > - add preempt_enable and use VM_FAULT_NOPAGE as failure code suggested by Yejian
> >
> > v2:
> > - commit message changes suggested by Greg
> >
> > v1: https://lore.kernel.org/lkml/CAJedcCzY72jqgF-pCPtx66vXXwdPn-KMagZnqrxcpWw1NxTLaA@xxxxxxxxxxxxxx/
> > ---
> > drivers/misc/sgi-gru/grufault.c | 14 ++++++++++++--
> > drivers/misc/sgi-gru/grumain.c | 18 ++++++++++++++----
> > drivers/misc/sgi-gru/grutables.h | 2 +-
> > 3 files changed, 27 insertions(+), 7 deletions(-)
> >
> > diff --git a/drivers/misc/sgi-gru/grufault.c b/drivers/misc/sgi-gru/grufault.c
> > index d7ef61e602ed..2b5b049fbd38 100644
> > --- a/drivers/misc/sgi-gru/grufault.c
> > +++ b/drivers/misc/sgi-gru/grufault.c
> > @@ -656,7 +656,9 @@ 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)
> > + goto err;
> >
> > /*
> > * CCH may contain stale data if ts_force_cch_reload is set.
> > @@ -677,6 +679,10 @@ int gru_handle_user_call_os(unsigned long cb)
> > exit:
> > gru_unlock_gts(gts);
> > return ret;
> > +err:
> > + gru_unlock_gts(gts);
> > + gru_unload_context(gts, 1);
> > + return -EINVAL;
> > }
> >
> > /*
> > @@ -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);
>
> In gru_set_context_option(), you are calling gru_unload_context() for all
> non-zero 'ret' values, but there are other instances where non-zero 'ret'
> values are being set that should not call gru_unload_context(). Maybe do
> this instead:
> if (gru_check_context_placement(gts)) {
> gru_unlock_gts(gts);
> gru_unload_context(gts, 1);
> return -EINVAL;
> }
>
> > }
> > 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..77becb52f550 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;
> >
> > if (!gru_check_chiplet_assignment(gru, gts)) {
> > STAT(check_context_unload);
> > - gru_unload_context(gts, 1);
> > + ret = -EINVAL;
> > } 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 +938,13 @@ 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) {
>
> One suggestion, there is now no need to declare 'ret'. Do this instead:
> if (gru_check_context_placement(gts)) {
>
> > + preempt_enable();
> > + mutex_unlock(&gts->ts_ctxlock);
> > + gru_unload_context(gts, 1);
> > + return VM_FAULT_NOPAGE;
> > + }
> >
> > if (!gts->ts_gru) {
> > STAT(load_user_context);
> > diff --git a/drivers/misc/sgi-gru/grutables.h b/drivers/misc/sgi-gru/grutables.h
> > index 5efc869fe59a..f4a5a787685f 100644
> > --- a/drivers/misc/sgi-gru/grutables.h
> > +++ b/drivers/misc/sgi-gru/grutables.h
> > @@ -632,7 +632,7 @@ extern int gru_user_flush_tlb(unsigned long arg);
> > extern int gru_user_unload_context(unsigned long arg);
> > extern int gru_get_exception_detail(unsigned long arg);
> > extern int gru_set_context_option(unsigned long address);
> > -extern void gru_check_context_placement(struct gru_thread_state *gts);
> > +extern int gru_check_context_placement(struct gru_thread_state *gts);
> > extern int gru_cpu_fault_map_id(void);
> > extern struct vm_area_struct *gru_find_vma(unsigned long vaddr);
> > extern void gru_flush_all_tlb(struct gru_state *gru);
> > --
> > 2.25.1