opp: Fix use-after-free in lazy_opp_tables after probe deferral

  When dev_pm_opp_of_find_icc_paths() in _allocate_opp_table() returns
-EPROBE_DEFER, the opp_table is freed again, to wait until all the
interconnect paths are available.

However, if the OPP table is using required-opps then it may already
have been added to the global lazy_opp_tables list. The error path
does not remove the opp_table from the list again.

This can cause crashes later when the provider of the required-opps
is added, since we will iterate over OPP tables that have already been
freed. E.g.:

  Unable to handle kernel NULL pointer dereference when read
  CPU: 0 PID: 7 Comm: kworker/0:0 Not tainted 6.4.0-rc3
  PC is at _of_add_opp_table_v2 (include/linux/of.h:949
  drivers/opp/of.c:98 drivers/opp/of.c:344 drivers/opp/of.c:404
  drivers/opp/of.c:1032) -> lazy_link_required_opp_table()

Fix this by removing the opp_table from the list before freeing it.

Cc: stable@vger.kernel.org
Fixes: 7eba0c7641b0 ("opp: Allow lazy-linking of required-opps")
Signed-off-by: Stephan Gerhold <stephan.gerhold@kernkonzept.com>
---
This fixes the crash I ran into after adding an OPP table with
both "required-opps" and interconnect paths (opp-peak-kBps).

By the way, the "lazy_opp_tables" does not seem to be protected by any
locks(?) so I could imagine that theoretically there could be a race
condition while adding/removing OPP tables there. This is unrelated
to the crash I saw, though.
---
 drivers/opp/core.c | 1 +
 1 file changed, 1 insertion(+)


---
base-commit: 9e28f7a74581204807f20ae46568939038e327aa
change-id: 20230524-opp-lazy-uaf-60a004b385ec

Best regards,
  

On 24-05-23, 19:56, Stephan Gerhold wrote:
> When dev_pm_opp_of_find_icc_paths() in _allocate_opp_table() returns
> -EPROBE_DEFER, the opp_table is freed again, to wait until all the
> interconnect paths are available.
> 
> However, if the OPP table is using required-opps then it may already
> have been added to the global lazy_opp_tables list. The error path
> does not remove the opp_table from the list again.
> 
> This can cause crashes later when the provider of the required-opps
> is added, since we will iterate over OPP tables that have already been
> freed. E.g.:
> 
>   Unable to handle kernel NULL pointer dereference when read
>   CPU: 0 PID: 7 Comm: kworker/0:0 Not tainted 6.4.0-rc3
>   PC is at _of_add_opp_table_v2 (include/linux/of.h:949
>   drivers/opp/of.c:98 drivers/opp/of.c:344 drivers/opp/of.c:404
>   drivers/opp/of.c:1032) -> lazy_link_required_opp_table()
> 
> Fix this by removing the opp_table from the list before freeing it.

I think you need this instead:

diff --git a/drivers/opp/core.c b/drivers/opp/core.c
index 954c94865cf5..b5973fefdfd8 100644
--- a/drivers/opp/core.c
+++ b/drivers/opp/core.c
@@ -1358,7 +1358,10 @@ static struct opp_table *_allocate_opp_table(struct device *dev, int index)
        return opp_table;

 remove_opp_dev:
+       _of_clear_opp_table(opp_table);
        _remove_opp_dev(opp_dev, opp_table);
+       mutex_destroy(&opp_table->genpd_virt_dev_lock);
+       mutex_destroy(&opp_table->lock);
 err:
        kfree(opp_table);
        return ERR_PTR(ret);

> Cc: stable@vger.kernel.org
> Fixes: 7eba0c7641b0 ("opp: Allow lazy-linking of required-opps")
> Signed-off-by: Stephan Gerhold <stephan.gerhold@kernkonzept.com>
> ---
> This fixes the crash I ran into after adding an OPP table with
> both "required-opps" and interconnect paths (opp-peak-kBps).
> 
> By the way, the "lazy_opp_tables" does not seem to be protected by any
> locks(?)

It is always accessed with opp_table_lock held I believe.
  

On Mon, May 29, 2023 at 11:01:48AM +0530, Viresh Kumar wrote:
> On 24-05-23, 19:56, Stephan Gerhold wrote:
> > When dev_pm_opp_of_find_icc_paths() in _allocate_opp_table() returns
> > -EPROBE_DEFER, the opp_table is freed again, to wait until all the
> > interconnect paths are available.
> > 
> > However, if the OPP table is using required-opps then it may already
> > have been added to the global lazy_opp_tables list. The error path
> > does not remove the opp_table from the list again.
> > 
> > This can cause crashes later when the provider of the required-opps
> > is added, since we will iterate over OPP tables that have already been
> > freed. E.g.:
> > 
> >   Unable to handle kernel NULL pointer dereference when read
> >   CPU: 0 PID: 7 Comm: kworker/0:0 Not tainted 6.4.0-rc3
> >   PC is at _of_add_opp_table_v2 (include/linux/of.h:949
> >   drivers/opp/of.c:98 drivers/opp/of.c:344 drivers/opp/of.c:404
> >   drivers/opp/of.c:1032) -> lazy_link_required_opp_table()
> > 
> > Fix this by removing the opp_table from the list before freeing it.
> 
> I think you need this instead:
> 
> diff --git a/drivers/opp/core.c b/drivers/opp/core.c
> index 954c94865cf5..b5973fefdfd8 100644
> --- a/drivers/opp/core.c
> +++ b/drivers/opp/core.c
> @@ -1358,7 +1358,10 @@ static struct opp_table *_allocate_opp_table(struct device *dev, int index)
>         return opp_table;
> 
>  remove_opp_dev:
> +       _of_clear_opp_table(opp_table);
>         _remove_opp_dev(opp_dev, opp_table);
> +       mutex_destroy(&opp_table->genpd_virt_dev_lock);
> +       mutex_destroy(&opp_table->lock);
>  err:
>         kfree(opp_table);
>         return ERR_PTR(ret);
> 

Thanks, this seems to fix the crash as well. Are you going to handle it
or should I send a v2 with this diff?

> > Cc: stable@vger.kernel.org
> > Fixes: 7eba0c7641b0 ("opp: Allow lazy-linking of required-opps")
> > Signed-off-by: Stephan Gerhold <stephan.gerhold@kernkonzept.com>
> > ---
> > This fixes the crash I ran into after adding an OPP table with
> > both "required-opps" and interconnect paths (opp-peak-kBps).
> > 
> > By the way, the "lazy_opp_tables" does not seem to be protected by any
> > locks(?)
> 
> It is always accessed with opp_table_lock held I believe.
> 

During _allocate_opp_table() it's accessed without the opp_table_lock,
because of

	/* Drop the lock to reduce the size of critical section */
	mutex_unlock(&opp_table_lock);

	if (opp_table) {
		/* ... */
		mutex_lock(&opp_table_lock);
	} else {
		opp_table = _allocate_opp_table(dev, index);

		mutex_lock(&opp_table_lock);
		/* ... */
	}

This doesn't seem to cause any problems in my case though so it's
unrelated to the crash I observed.

Thanks,
Stephan
  

On 30-05-23, 10:31, Stephan Gerhold wrote:
> Thanks, this seems to fix the crash as well. Are you going to handle it
> or should I send a v2 with this diff?

Please send a V2 :)

> During _allocate_opp_table() it's accessed without the opp_table_lock,
> because of
> 
> 	/* Drop the lock to reduce the size of critical section */
> 	mutex_unlock(&opp_table_lock);
> 
> 	if (opp_table) {
> 		/* ... */
> 		mutex_lock(&opp_table_lock);
> 	} else {
> 		opp_table = _allocate_opp_table(dev, index);
> 
> 		mutex_lock(&opp_table_lock);
> 		/* ... */
> 	}
> 
> This doesn't seem to cause any problems in my case though so it's
> unrelated to the crash I observed.

Hmm, right. Maybe we need a lock for that list, want to take that up ?
  

On Tue, May 30, 2023 at 02:43:30PM +0530, Viresh Kumar wrote:
> On 30-05-23, 10:31, Stephan Gerhold wrote:
> > Thanks, this seems to fix the crash as well. Are you going to handle it
> > or should I send a v2 with this diff?
> 
> Please send a V2 :)
> 

Done!

> > During _allocate_opp_table() it's accessed without the opp_table_lock,
> > because of
> > 
> > 	/* Drop the lock to reduce the size of critical section */
> > 	mutex_unlock(&opp_table_lock);
> > 
> > 	if (opp_table) {
> > 		/* ... */
> > 		mutex_lock(&opp_table_lock);
> > 	} else {
> > 		opp_table = _allocate_opp_table(dev, index);
> > 
> > 		mutex_lock(&opp_table_lock);
> > 		/* ... */
> > 	}
> > 
> > This doesn't seem to cause any problems in my case though so it's
> > unrelated to the crash I observed.
> 
> Hmm, right. Maybe we need a lock for that list, want to take that up ?
> 

Yeah, a lock would probably be good to be safe. I would appreciate if
you or someone else could create a patch for this though, since I'm not
too familiar with the overall OPP implementation. I would be happy to
test that it works properly for my apparently quite special use case
(I have several OPP tables with interconnects and required-opps).

Thanks!
Stephan