From: Dongliang Mu <[email protected]>
The error handling code of peak_usb_create_dev forgets to reset the
next_siblings of previous entry.
Fix this by nullifying the (dev->prev_siblings)->next_siblings in the
error handling code.
Signed-off-by: Dongliang Mu <[email protected]>
---
drivers/net/can/usb/peak_usb/pcan_usb_core.c | 3 +++
1 file changed, 3 insertions(+)
diff --git a/drivers/net/can/usb/peak_usb/pcan_usb_core.c b/drivers/net/can/usb/peak_usb/pcan_usb_core.c
index b850ff8fe4bd..f858810221b6 100644
--- a/drivers/net/can/usb/peak_usb/pcan_usb_core.c
+++ b/drivers/net/can/usb/peak_usb/pcan_usb_core.c
@@ -894,6 +894,9 @@ static int peak_usb_create_dev(const struct peak_usb_adapter *peak_usb_adapter,
dev->adapter->dev_free(dev);
lbl_unregister_candev:
+ /* remove the dangling pointer in next_siblings */
+ if (dev->prev_siblings)
+ (dev->prev_siblings)->next_siblings = NULL;
unregister_candev(netdev);
lbl_restore_intf_data:
--
2.25.1
Hi Dongliang,
On 1/20/22 16:05, Dongliang Mu wrote:
> From: Dongliang Mu <[email protected]>
>
> The error handling code of peak_usb_create_dev forgets to reset the
> next_siblings of previous entry.
>
> Fix this by nullifying the (dev->prev_siblings)->next_siblings in the
> error handling code.
>
> Signed-off-by: Dongliang Mu <[email protected]>
> ---
> drivers/net/can/usb/peak_usb/pcan_usb_core.c | 3 +++
> 1 file changed, 3 insertions(+)
>
> diff --git a/drivers/net/can/usb/peak_usb/pcan_usb_core.c b/drivers/net/can/usb/peak_usb/pcan_usb_core.c
> index b850ff8fe4bd..f858810221b6 100644
> --- a/drivers/net/can/usb/peak_usb/pcan_usb_core.c
> +++ b/drivers/net/can/usb/peak_usb/pcan_usb_core.c
> @@ -894,6 +894,9 @@ static int peak_usb_create_dev(const struct peak_usb_adapter *peak_usb_adapter,
> dev->adapter->dev_free(dev);
>
> lbl_unregister_candev:
> + /* remove the dangling pointer in next_siblings */
> + if (dev->prev_siblings)
> + (dev->prev_siblings)->next_siblings = NULL;
> unregister_candev(netdev);
>
> lbl_restore_intf_data:
Is this pointer used somewhere? I see, that couple of
struct peak_usb_adapter::dev_free() functions use it, but
peak_usb_disconnect() sets dev->next_siblings to NULL before calling
->dev_free().
Do you have a calltrace or oops log?
With regards,
Pavel Skripkin
On Thu, Jan 20, 2022 at 10:27 PM Pavel Skripkin <[email protected]> wrote:
>
> Hi Dongliang,
>
> On 1/20/22 16:05, Dongliang Mu wrote:
> > From: Dongliang Mu <[email protected]>
> >
> > The error handling code of peak_usb_create_dev forgets to reset the
> > next_siblings of previous entry.
> >
> > Fix this by nullifying the (dev->prev_siblings)->next_siblings in the
> > error handling code.
> >
> > Signed-off-by: Dongliang Mu <[email protected]>
> > ---
> > drivers/net/can/usb/peak_usb/pcan_usb_core.c | 3 +++
> > 1 file changed, 3 insertions(+)
> >
> > diff --git a/drivers/net/can/usb/peak_usb/pcan_usb_core.c b/drivers/net/can/usb/peak_usb/pcan_usb_core.c
> > index b850ff8fe4bd..f858810221b6 100644
> > --- a/drivers/net/can/usb/peak_usb/pcan_usb_core.c
> > +++ b/drivers/net/can/usb/peak_usb/pcan_usb_core.c
> > @@ -894,6 +894,9 @@ static int peak_usb_create_dev(const struct peak_usb_adapter *peak_usb_adapter,
> > dev->adapter->dev_free(dev);
> >
> > lbl_unregister_candev:
> > + /* remove the dangling pointer in next_siblings */
> > + if (dev->prev_siblings)
> > + (dev->prev_siblings)->next_siblings = NULL;
> > unregister_candev(netdev);
> >
> > lbl_restore_intf_data:
>
>
> Is this pointer used somewhere? I see, that couple of
> struct peak_usb_adapter::dev_free() functions use it, but
> peak_usb_disconnect() sets dev->next_siblings to NULL before calling
> ->dev_free().
>
> Do you have a calltrace or oops log?
Hi Pavel,
I have no calltrace or log since this dangling pointer may not be
dereferenced in the following code. But I am not sure. So the commit
title of this patch is "remove a dangling pointer in
peak_usb_create_dev".
>
>
>
>
> With regards,
> Pavel Skripkin
On Fri, Jan 21, 2022 at 8:09 AM Dongliang Mu <[email protected]> wrote:
>
> On Thu, Jan 20, 2022 at 10:27 PM Pavel Skripkin <[email protected]> wrote:
> >
> > Hi Dongliang,
> >
> > On 1/20/22 16:05, Dongliang Mu wrote:
> > > From: Dongliang Mu <[email protected]>
> > >
> > > The error handling code of peak_usb_create_dev forgets to reset the
> > > next_siblings of previous entry.
> > >
> > > Fix this by nullifying the (dev->prev_siblings)->next_siblings in the
> > > error handling code.
> > >
> > > Signed-off-by: Dongliang Mu <[email protected]>
> > > ---
> > > drivers/net/can/usb/peak_usb/pcan_usb_core.c | 3 +++
> > > 1 file changed, 3 insertions(+)
> > >
> > > diff --git a/drivers/net/can/usb/peak_usb/pcan_usb_core.c b/drivers/net/can/usb/peak_usb/pcan_usb_core.c
> > > index b850ff8fe4bd..f858810221b6 100644
> > > --- a/drivers/net/can/usb/peak_usb/pcan_usb_core.c
> > > +++ b/drivers/net/can/usb/peak_usb/pcan_usb_core.c
> > > @@ -894,6 +894,9 @@ static int peak_usb_create_dev(const struct peak_usb_adapter *peak_usb_adapter,
> > > dev->adapter->dev_free(dev);
> > >
> > > lbl_unregister_candev:
> > > + /* remove the dangling pointer in next_siblings */
> > > + if (dev->prev_siblings)
> > > + (dev->prev_siblings)->next_siblings = NULL;
> > > unregister_candev(netdev);
> > >
> > > lbl_restore_intf_data:
> >
> >
> > Is this pointer used somewhere? I see, that couple of
> > struct peak_usb_adapter::dev_free() functions use it, but
> > peak_usb_disconnect() sets dev->next_siblings to NULL before calling
> > ->dev_free().
> >
> > Do you have a calltrace or oops log?
>
> Hi Pavel,
>
> I have no calltrace or log since this dangling pointer may not be
> dereferenced in the following code. But I am not sure. So the commit
> title of this patch is "remove a dangling pointer in
> peak_usb_create_dev".
BTW, as you mentioned, dev->next_siblings is used in struct
peak_usb_adapter::dev_free() (i.e., pcan_usb_fd_free or
pcan_usb_pro_free), how about the following path?
peak_usb_probe
-> peak_usb_create_dev (goto adap_dev_free;)
-> dev->adapter->dev_free()
-> pcan_usb_fd_free or pcan_usb_pro_free (This function uses
next_siblings as condition elements)
static void pcan_usb_fd_free(struct peak_usb_device *dev)
{
/* last device: can free shared objects now */
if (!dev->prev_siblings && !dev->next_siblings) {
struct pcan_usb_fd_device *pdev =
container_of(dev, struct pcan_usb_fd_device, dev);
/* free commands buffer */
kfree(pdev->cmd_buffer_addr);
/* free usb interface object */
kfree(pdev->usb_if);
}
}
If next_siblings is not NULL, will it lead to the missing free of
cmd_buffer_addr and usb_if?
Please let me know if I made any mistakes.
> >
> >
> >
> >
> > With regards,
> > Pavel Skripkin
On Fri, Jan 21, 2022 at 11:36 AM Dongliang Mu <[email protected]> wrote:
>
> On Fri, Jan 21, 2022 at 8:09 AM Dongliang Mu <[email protected]> wrote:
> >
> > On Thu, Jan 20, 2022 at 10:27 PM Pavel Skripkin <[email protected]> wrote:
> > >
> > > Hi Dongliang,
> > >
> > > On 1/20/22 16:05, Dongliang Mu wrote:
> > > > From: Dongliang Mu <[email protected]>
> > > >
> > > > The error handling code of peak_usb_create_dev forgets to reset the
> > > > next_siblings of previous entry.
> > > >
> > > > Fix this by nullifying the (dev->prev_siblings)->next_siblings in the
> > > > error handling code.
> > > >
> > > > Signed-off-by: Dongliang Mu <[email protected]>
> > > > ---
> > > > drivers/net/can/usb/peak_usb/pcan_usb_core.c | 3 +++
> > > > 1 file changed, 3 insertions(+)
> > > >
> > > > diff --git a/drivers/net/can/usb/peak_usb/pcan_usb_core.c b/drivers/net/can/usb/peak_usb/pcan_usb_core.c
> > > > index b850ff8fe4bd..f858810221b6 100644
> > > > --- a/drivers/net/can/usb/peak_usb/pcan_usb_core.c
> > > > +++ b/drivers/net/can/usb/peak_usb/pcan_usb_core.c
> > > > @@ -894,6 +894,9 @@ static int peak_usb_create_dev(const struct peak_usb_adapter *peak_usb_adapter,
> > > > dev->adapter->dev_free(dev);
> > > >
> > > > lbl_unregister_candev:
> > > > + /* remove the dangling pointer in next_siblings */
> > > > + if (dev->prev_siblings)
> > > > + (dev->prev_siblings)->next_siblings = NULL;
> > > > unregister_candev(netdev);
> > > >
> > > > lbl_restore_intf_data:
> > >
> > >
> > > Is this pointer used somewhere? I see, that couple of
> > > struct peak_usb_adapter::dev_free() functions use it, but
> > > peak_usb_disconnect() sets dev->next_siblings to NULL before calling
> > > ->dev_free().
> > >
> > > Do you have a calltrace or oops log?
> >
> > Hi Pavel,
> >
> > I have no calltrace or log since this dangling pointer may not be
> > dereferenced in the following code. But I am not sure. So the commit
> > title of this patch is "remove a dangling pointer in
> > peak_usb_create_dev".
>
> BTW, as you mentioned, dev->next_siblings is used in struct
> peak_usb_adapter::dev_free() (i.e., pcan_usb_fd_free or
> pcan_usb_pro_free), how about the following path?
>
> peak_usb_probe
> -> peak_usb_create_dev (goto adap_dev_free;)
> -> dev->adapter->dev_free()
> -> pcan_usb_fd_free or pcan_usb_pro_free (This function uses
> next_siblings as condition elements)
>
> static void pcan_usb_fd_free(struct peak_usb_device *dev)
> {
> /* last device: can free shared objects now */
> if (!dev->prev_siblings && !dev->next_siblings) {
> struct pcan_usb_fd_device *pdev =
> container_of(dev, struct pcan_usb_fd_device, dev);
>
> /* free commands buffer */
> kfree(pdev->cmd_buffer_addr);
>
> /* free usb interface object */
> kfree(pdev->usb_if);
> }
> }
>
> If next_siblings is not NULL, will it lead to the missing free of
> cmd_buffer_addr and usb_if?
The answer is No. Forget my silly thought.
>
> Please let me know if I made any mistakes.
>
> > >
> > >
> > >
> > >
> > > With regards,
> > > Pavel Skripkin
Hi Dongliang,
On 1/21/22 08:58, Dongliang Mu wrote:
[...]>> BTW, as you mentioned, dev->next_siblings is used in struct
>> peak_usb_adapter::dev_free() (i.e., pcan_usb_fd_free or
>> pcan_usb_pro_free), how about the following path?
>>
>> peak_usb_probe
>> -> peak_usb_create_dev (goto adap_dev_free;)
>> -> dev->adapter->dev_free()
>> -> pcan_usb_fd_free or pcan_usb_pro_free (This function uses
>> next_siblings as condition elements)
>>
>> static void pcan_usb_fd_free(struct peak_usb_device *dev)
>> {
>> /* last device: can free shared objects now */
>> if (!dev->prev_siblings && !dev->next_siblings) {
>> struct pcan_usb_fd_device *pdev =
>> container_of(dev, struct pcan_usb_fd_device, dev);
>>
>> /* free commands buffer */
>> kfree(pdev->cmd_buffer_addr);
>>
>> /* free usb interface object */
>> kfree(pdev->usb_if);
>> }
>> }
>>
>> If next_siblings is not NULL, will it lead to the missing free of
>> cmd_buffer_addr and usb_if?
>
> The answer is No. Forget my silly thought.
>
Yeah, it seems like (at least based on code), that this dangling pointer
is not dangerous, since nothing accesses it. And next_siblings
_guaranteed_ to be NULL, since dev->next_siblings is set NULL in
disconnect()
With regards,
Pavel Skripkin
On Sat, Jan 22, 2022 at 3:36 AM Pavel Skripkin <[email protected]> wrote:
>
> Hi Dongliang,
>
> On 1/21/22 08:58, Dongliang Mu wrote:
> [...]>> BTW, as you mentioned, dev->next_siblings is used in struct
> >> peak_usb_adapter::dev_free() (i.e., pcan_usb_fd_free or
> >> pcan_usb_pro_free), how about the following path?
> >>
> >> peak_usb_probe
> >> -> peak_usb_create_dev (goto adap_dev_free;)
> >> -> dev->adapter->dev_free()
> >> -> pcan_usb_fd_free or pcan_usb_pro_free (This function uses
> >> next_siblings as condition elements)
> >>
> >> static void pcan_usb_fd_free(struct peak_usb_device *dev)
> >> {
> >> /* last device: can free shared objects now */
> >> if (!dev->prev_siblings && !dev->next_siblings) {
> >> struct pcan_usb_fd_device *pdev =
> >> container_of(dev, struct pcan_usb_fd_device, dev);
> >>
> >> /* free commands buffer */
> >> kfree(pdev->cmd_buffer_addr);
> >>
> >> /* free usb interface object */
> >> kfree(pdev->usb_if);
> >> }
> >> }
> >>
> >> If next_siblings is not NULL, will it lead to the missing free of
> >> cmd_buffer_addr and usb_if?
> >
> > The answer is No. Forget my silly thought.
> >
>
> Yeah, it seems like (at least based on code), that this dangling pointer
> is not dangerous, since nothing accesses it. And next_siblings
> _guaranteed_ to be NULL, since dev->next_siblings is set NULL in
> disconnect()
Yes, you're right. As a security researcher, I am sensitive to such
dangling pointers.
As its nullifying site is across functions, I suggest developers
remove this dangling pointer in case that any newly added code in this
function or before the nullifying location would touch next_siblings.
If Pavel and others think it's fine, then it's time to close this patch.
>
>
>
>
> With regards,
> Pavel Skripkin
Hi Dongliang,
On 1/22/22 09:45, Dongliang Mu wrote:
[...]
>> Yeah, it seems like (at least based on code), that this dangling pointer
>> is not dangerous, since nothing accesses it. And next_siblings
>> _guaranteed_ to be NULL, since dev->next_siblings is set NULL in
>> disconnect()
>
> Yes, you're right. As a security researcher, I am sensitive to such
> dangling pointers.
>
> As its nullifying site is across functions, I suggest developers
> remove this dangling pointer in case that any newly added code in this
> function or before the nullifying location would touch next_siblings.
>
Based on git blame this driver is very old (was added in 2012), so, I
guess, nothing really new will come up.
Anyway, I am absolutely not a security person and if you think, that
this dangling pointer can be somehow used in exploitation you should
state it in commit message.
> If Pavel and others think it's fine, then it's time to close this patch.
>
I don't have any big objections on the code itself. Maybe only 'if' can
be removed to just speed up the code, but I don't see why this change is
needed :)
With regards,
Pavel Skripkin
On Sun, Jan 23, 2022 at 9:48 PM Pavel Skripkin <[email protected]> wrote:
>
> Hi Dongliang,
>
> On 1/22/22 09:45, Dongliang Mu wrote:
> [...]
>
> >> Yeah, it seems like (at least based on code), that this dangling pointer
> >> is not dangerous, since nothing accesses it. And next_siblings
> >> _guaranteed_ to be NULL, since dev->next_siblings is set NULL in
> >> disconnect()
> >
> > Yes, you're right. As a security researcher, I am sensitive to such
> > dangling pointers.
> >
> > As its nullifying site is across functions, I suggest developers
> > remove this dangling pointer in case that any newly added code in this
> > function or before the nullifying location would touch next_siblings.
> >
>
> Based on git blame this driver is very old (was added in 2012), so, I
> guess, nothing really new will come up.
>
> Anyway, I am absolutely not a security person and if you think, that
> this dangling pointer can be somehow used in exploitation you should
> state it in commit message.
>
>
> > If Pavel and others think it's fine, then it's time to close this patch.
> >
>
> I don't have any big objections on the code itself. Maybe only 'if' can
> be removed to just speed up the code, but I don't see why this change is
> needed :)
OK, let's move on. Leave alone this patch.
>
>
>
>
> With regards,
> Pavel Skripkin