(Added linux-wireless, since this is a wireless driver)
On Sunday, April 9, 2017 10:23:20 PM CEST Myungho Jung wrote:
> Kernel panic is caused by trying to dereference null pointer. Check if
> the pointer is null before freeing space.
Do you have the kernel panic somewhere?
I think you have an even bigger problem: You see, in order to get EEPROM
readback and rx_stats feedback you need to sent a request to the firmware
and if the response's req_id cookies don't match, you end up filling up
the very limited device address space.
As for adding if (!skb) checks. I think kfree, kfree_skb, dev_kfree_skb
(aka consume_skb) all check for null pointers already. So the logical
thing to do would be to make dev_kfree_skb_irq (which would also fix
dev_kfree_skb_any) consistent with kfree, kfree_skb, dev_kfree_skb and
add the check there.
> Signed-off-by: Myungho Jung <[email protected]>
> ---
> drivers/net/wireless/intersil/p54/txrx.c | 8 ++++++--
> 1 file changed, 6 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/net/wireless/intersil/p54/txrx.c b/drivers/net/wireless/intersil/p54/txrx.c
> index 1af7da0..8956061 100644
> --- a/drivers/net/wireless/intersil/p54/txrx.c
> +++ b/drivers/net/wireless/intersil/p54/txrx.c
> @@ -503,7 +503,9 @@ static void p54_rx_eeprom_readback(struct p54_common *priv,
>
> priv->eeprom = NULL;
> tmp = p54_find_and_unlink_skb(priv, hdr->req_id);
> - dev_kfree_skb_any(tmp);
> + if (unlikely(!tmp))
> + dev_kfree_skb_any(tmp);
> +
> complete(&priv->eeprom_comp);
> }
>
> @@ -597,7 +599,9 @@ static void p54_rx_stats(struct p54_common *priv, struct sk_buff *skb)
> }
>
> tmp = p54_find_and_unlink_skb(priv, hdr->req_id);
> - dev_kfree_skb_any(tmp);
> + if (unlikely(!tmp))
> + dev_kfree_skb_any(tmp);
> +
> complete(&priv->stat_comp);
> }
>
>
On Mon, Apr 10, 2017 at 02:12:54PM +0200, Christian Lamparter wrote:
> (Added linux-wireless, since this is a wireless driver)
>
> On Sunday, April 9, 2017 10:23:20 PM CEST Myungho Jung wrote:
> > Kernel panic is caused by trying to dereference null pointer. Check if
> > the pointer is null before freeing space.
> Do you have the kernel panic somewhere?
> I think you have an even bigger problem: You see, in order to get EEPROM
> readback and rx_stats feedback you need to sent a request to the firmware
> and if the response's req_id cookies don't match, you end up filling up
> the very limited device address space.
>
> As for adding if (!skb) checks. I think kfree, kfree_skb, dev_kfree_skb
> (aka consume_skb) all check for null pointers already. So the logical
> thing to do would be to make dev_kfree_skb_irq (which would also fix
> dev_kfree_skb_any) consistent with kfree, kfree_skb, dev_kfree_skb and
> add the check there.
>
> > Signed-off-by: Myungho Jung <[email protected]>
> > ---
> > drivers/net/wireless/intersil/p54/txrx.c | 8 ++++++--
> > 1 file changed, 6 insertions(+), 2 deletions(-)
> >
> > diff --git a/drivers/net/wireless/intersil/p54/txrx.c b/drivers/net/wireless/intersil/p54/txrx.c
> > index 1af7da0..8956061 100644
> > --- a/drivers/net/wireless/intersil/p54/txrx.c
> > +++ b/drivers/net/wireless/intersil/p54/txrx.c
> > @@ -503,7 +503,9 @@ static void p54_rx_eeprom_readback(struct p54_common *priv,
> >
> > priv->eeprom = NULL;
> > tmp = p54_find_and_unlink_skb(priv, hdr->req_id);
> > - dev_kfree_skb_any(tmp);
> > + if (unlikely(!tmp))
> > + dev_kfree_skb_any(tmp);
> > +
> > complete(&priv->eeprom_comp);
> > }
> >
> > @@ -597,7 +599,9 @@ static void p54_rx_stats(struct p54_common *priv, struct sk_buff *skb)
> > }
> >
> > tmp = p54_find_and_unlink_skb(priv, hdr->req_id);
> > - dev_kfree_skb_any(tmp);
> > + if (unlikely(!tmp))
> > + dev_kfree_skb_any(tmp);
> > +
> > complete(&priv->stat_comp);
> > }
> >
> >
>
>
I found that the fix was totally opposite to my thought. Sorry about
confusion. I'm not sure it actually caused kernel panic but guessed from
a bug report [https://bugzilla.kernel.org/show_bug.cgi?id=195289]. And
correct fix will be like this:
if (likely(tmp))
dev_kfree_skb_any(tmp);
But, like you said, I think null pointer should be checked in
dev_kfree_skb_irq although already checking before calling it in many
other places. I'll try another patch. Thank you for your advice.
Thanks,
Myungho
On Mon, Apr 10, 2017 at 2:22 PM, Christian Lamparter
<[email protected]> wrote:
> Well, the patch could be as simple as this:
> ---
> diff --git a/net/core/dev.c b/net/core/dev.c
> index 7869ae3837ca..44f7d5a1c67c 100644
> --- a/net/core/dev.c
> +++ b/net/core/dev.c
> @@ -2450,6 +2450,9 @@ void __dev_kfree_skb_irq(struct sk_buff *skb, enum skb_free_reason reason)
> {
> unsigned long flags;
>
> + if (!skb)
> + return;
> +
> if (likely(atomic_read(&skb->users) == 1)) {
> smp_rmb();
> atomic_set(&skb->users, 0);
> ---
>
> The question is: would David or Eric support the change. Any comments,
> what's the prefered solution? Just patch __dev_kfree_skb_irq to make
> it consistent with *kfree*, or patch the driver? I'm fine either way,
> but I would prefere patching __dev_kfree_skb_irq.
This is fine, same check happens in consume_skb()
On Monday, April 10, 2017 1:54:14 PM CEST Myungho Jung wrote:
> On Mon, Apr 10, 2017 at 02:12:54PM +0200, Christian Lamparter wrote:
> > On Sunday, April 9, 2017 10:23:20 PM CEST Myungho Jung wrote:
> > > Kernel panic is caused by trying to dereference null pointer. Check if
> > > the pointer is null before freeing space.
> > [...]
> > As for adding if (!skb) checks. I think kfree, kfree_skb, dev_kfree_skb
> > (aka consume_skb) all check for null pointers already. So the logical
> > thing to do would be to make dev_kfree_skb_irq (which would also fix
> > dev_kfree_skb_any) consistent with kfree, kfree_skb, dev_kfree_skb and
> > add the check there.
> > > ---
> > > drivers/net/wireless/intersil/p54/txrx.c | 8 ++++++--
> > > 1 file changed, 6 insertions(+), 2 deletions(-)
> > >
> > > diff --git a/drivers/net/wireless/intersil/p54/txrx.c b/drivers/net/wireless/intersil/p54/txrx.c
> > > index 1af7da0..8956061 100644
> > > --- a/drivers/net/wireless/intersil/p54/txrx.c
> > > +++ b/drivers/net/wireless/intersil/p54/txrx.c
> > > @@ -503,7 +503,9 @@ static void p54_rx_eeprom_readback(struct p54_common *priv,
> > >
> > > priv->eeprom = NULL;
> > > tmp = p54_find_and_unlink_skb(priv, hdr->req_id);
> > > - dev_kfree_skb_any(tmp);
> > > + if (unlikely(!tmp))
> > > + dev_kfree_skb_any(tmp);
> > > +
> > > complete(&priv->eeprom_comp);
> > > }
> > >
> > > @@ -597,7 +599,9 @@ static void p54_rx_stats(struct p54_common *priv, struct sk_buff *skb)
> > > }
> > >
> > > tmp = p54_find_and_unlink_skb(priv, hdr->req_id);
> > > - dev_kfree_skb_any(tmp);
> > > + if (unlikely(!tmp))
> > > + dev_kfree_skb_any(tmp);
> > > +
> > > complete(&priv->stat_comp);
> > > }
> > >
> > >
> >
> >
> [...] I'm not sure it actually caused kernel panic but guessed from
> a bug report [https://bugzilla.kernel.org/show_bug.cgi?id=195289].
Thank you for bringing this to my attention. Reading the bugreport, it
does sound like there's a bigger issue with the USB Ports. I'll see if
this can be fixed. But it does sound like a hardware issue at this
point.
> And correct fix will be like this:
> if (likely(tmp))
> dev_kfree_skb_any(tmp);
>
> But, like you said, I think null pointer should be checked in
> dev_kfree_skb_irq although already checking before calling it in many
> other places. I'll try another patch. Thank you for your advice.
Well, the patch could be as simple as this:
---
diff --git a/net/core/dev.c b/net/core/dev.c
index 7869ae3837ca..44f7d5a1c67c 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -2450,6 +2450,9 @@ void __dev_kfree_skb_irq(struct sk_buff *skb, enum skb_free_reason reason)
{
unsigned long flags;
+ if (!skb)
+ return;
+
if (likely(atomic_read(&skb->users) == 1)) {
smp_rmb();
atomic_set(&skb->users, 0);
---
The question is: would David or Eric support the change. Any comments,
what's the prefered solution? Just patch __dev_kfree_skb_irq to make
it consistent with *kfree*, or patch the driver? I'm fine either way,
but I would prefere patching __dev_kfree_skb_irq.
Regards,
Christian