[PATCH] net: stmmac: ensure jumbo_frm error return is correctly checked for -ve value

[PATCH] net: stmmac: ensure jumbo_frm error return is correctly checked for -ve value

[Colin King]

From: Colin Ian King <colin.king@canonical.com>

The current comparison of entry < 0 will never be true since entry is an
unsigned integer. Cast entry to an int to ensure -ve error return values
from the call to jumbo_frm are correctly being caught.

Detected by CoverityScan, CID#1238760 ("Macro compares unsigned to 0")

Signed-off-by: Colin Ian King <colin.king@canonical.com>
---
 drivers/net/ethernet/stmicro/stmmac/stmmac_main.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
index 68a188e74c54..5cc19506ba85 100644
--- a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
+++ b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
@@ -2996,7 +2996,7 @@ static netdev_tx_t stmmac_xmit(struct sk_buff *skb, struct net_device *dev)
 	if (unlikely(is_jumbo) && likely(priv->synopsys_id <
 					 DWMAC_CORE_4_00)) {
 		entry = priv->hw->mode->jumbo_frm(tx_q, skb, csum_insertion);
-		if (unlikely(entry < 0))
+		if (unlikely((int)entry < 0))
 			goto dma_map_err;
 	}
 
-- 
2.11.0

[PATCH] net: stmmac: ensure jumbo_frm error return is correctly checked for -ve value

[Colin King]

From: Colin Ian King <colin.king@canonical.com>

The current comparison of entry < 0 will never be true since entry is an
unsigned integer. Cast entry to an int to ensure -ve error return values
from the call to jumbo_frm are correctly being caught.

Detected by CoverityScan, CID#1238760 ("Macro compares unsigned to 0")

Signed-off-by: Colin Ian King <colin.king@canonical.com>
---
 drivers/net/ethernet/stmicro/stmmac/stmmac_main.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
index 68a188e74c54..5cc19506ba85 100644
--- a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
+++ b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
@@ -2996,7 +2996,7 @@ static netdev_tx_t stmmac_xmit(struct sk_buff *skb, struct net_device *dev)
 	if (unlikely(is_jumbo) && likely(priv->synopsys_id <
 					 DWMAC_CORE_4_00)) {
 		entry = priv->hw->mode->jumbo_frm(tx_q, skb, csum_insertion);
-		if (unlikely(entry < 0))
+		if (unlikely((int)entry < 0))
 			goto dma_map_err;
 	}
 
-- 
2.11.0

Re: [PATCH] net: stmmac: ensure jumbo_frm error return is correctly checked for -ve value

[Andy Shevchenko]

On Fri, Jun 2, 2017 at 5:58 PM, Colin King <colin.king@canonical.com> wrote:
> The current comparison of entry < 0 will never be true since entry is an
> unsigned integer. Cast entry to an int to ensure -ve error return values
> from the call to jumbo_frm are correctly being caught.

>         if (unlikely(is_jumbo) && likely(priv->synopsys_id <
>                                          DWMAC_CORE_4_00)) {
>                 entry = priv->hw->mode->jumbo_frm(tx_q, skb, csum_insertion);
> -               if (unlikely(entry < 0))
> +               if (unlikely((int)entry < 0))

It feels like a hiding some other issue.

-- 
With Best Regards,
Andy Shevchenko

Re: [PATCH] net: stmmac: ensure jumbo_frm error return is correctly checked for -ve value

[Andy Shevchenko]

On Fri, Jun 2, 2017 at 5:58 PM, Colin King <colin.king@canonical.com> wrote:
> The current comparison of entry < 0 will never be true since entry is an
> unsigned integer. Cast entry to an int to ensure -ve error return values
> from the call to jumbo_frm are correctly being caught.

>         if (unlikely(is_jumbo) && likely(priv->synopsys_id <
>                                          DWMAC_CORE_4_00)) {
>                 entry = priv->hw->mode->jumbo_frm(tx_q, skb, csum_insertion);
> -               if (unlikely(entry < 0))
> +               if (unlikely((int)entry < 0))

It feels like a hiding some other issue.

-- 
With Best Regards,
Andy Shevchenko

Re: [PATCH] net: stmmac: ensure jumbo_frm error return is correctly checked for -ve value

[Colin Ian King]

On 03/06/17 16:55, Andy Shevchenko wrote:
> On Fri, Jun 2, 2017 at 5:58 PM, Colin King <colin.king@canonical.com> wrote:
>> The current comparison of entry < 0 will never be true since entry is an
>> unsigned integer. Cast entry to an int to ensure -ve error return values
>> from the call to jumbo_frm are correctly being caught.
> 
>>         if (unlikely(is_jumbo) && likely(priv->synopsys_id <
>>                                          DWMAC_CORE_4_00)) {
>>                 entry = priv->hw->mode->jumbo_frm(tx_q, skb, csum_insertion);
>> -               if (unlikely(entry < 0))
>> +               if (unlikely((int)entry < 0))
> 
> It feels like a hiding some other issue.
> 

The alternative is:

		int rc = priv->hw->mode->jumbo_frm(tx_q, skb, csum_insertion);
		if (unlikely(rc < 0))
			goto dma_map_err;

		entry = rc;

however, that is effectively the same. The cast I'm using is a well used
idiom in the kernel, it used in almost a hundred similar cases.

git grep "< 0" | grep "(int)" | wc -l
95

Colin

Re: [PATCH] net: stmmac: ensure jumbo_frm error return is correctly checked for -ve value

[Colin Ian King]

On 03/06/17 16:55, Andy Shevchenko wrote:
> On Fri, Jun 2, 2017 at 5:58 PM, Colin King <colin.king@canonical.com> wrote:
>> The current comparison of entry < 0 will never be true since entry is an
>> unsigned integer. Cast entry to an int to ensure -ve error return values
>> from the call to jumbo_frm are correctly being caught.
> 
>>         if (unlikely(is_jumbo) && likely(priv->synopsys_id <
>>                                          DWMAC_CORE_4_00)) {
>>                 entry = priv->hw->mode->jumbo_frm(tx_q, skb, csum_insertion);
>> -               if (unlikely(entry < 0))
>> +               if (unlikely((int)entry < 0))
> 
> It feels like a hiding some other issue.
> 

The alternative is:

		int rc = priv->hw->mode->jumbo_frm(tx_q, skb, csum_insertion);
		if (unlikely(rc < 0))
			goto dma_map_err;

		entry = rc;

however, that is effectively the same. The cast I'm using is a well used
idiom in the kernel, it used in almost a hundred similar cases.

git grep "< 0" | grep "(int)" | wc -l
95

Colin

Re: [PATCH] net: stmmac: ensure jumbo_frm error return is correctly checked for -ve value

[Julia Lawall]

On Sat, 3 Jun 2017, Colin Ian King wrote:

> On 03/06/17 16:55, Andy Shevchenko wrote:
> > On Fri, Jun 2, 2017 at 5:58 PM, Colin King <colin.king@canonical.com> wrote:
> >> The current comparison of entry < 0 will never be true since entry is an
> >> unsigned integer. Cast entry to an int to ensure -ve error return values
> >> from the call to jumbo_frm are correctly being caught.
> >
> >>         if (unlikely(is_jumbo) && likely(priv->synopsys_id <
> >>                                          DWMAC_CORE_4_00)) {
> >>                 entry = priv->hw->mode->jumbo_frm(tx_q, skb, csum_insertion);
> >> -               if (unlikely(entry < 0))
> >> +               if (unlikely((int)entry < 0))
> >
> > It feels like a hiding some other issue.
> >
>
> The alternative is:
>
> 		int rc = priv->hw->mode->jumbo_frm(tx_q, skb, csum_insertion);
> 		if (unlikely(rc < 0))
> 			goto dma_map_err;
>
> 		entry = rc;
>
> however, that is effectively the same. The cast I'm using is a well used
> idiom in the kernel, it used in almost a hundred similar cases.
>
> git grep "< 0" | grep "(int)" | wc -l
> 95

Does entry really have to be unsigned?  The jumbo_frm function returns an
int, not an unsigned int, so it seems unpleasant to make it unsigned
prematurely just to put a cast afterwards.  The remaining computation
seems to involve only small numbers.

julia

Re: [PATCH] net: stmmac: ensure jumbo_frm error return is correctly checked for -ve value

[Julia Lawall]

On Sat, 3 Jun 2017, Colin Ian King wrote:

> On 03/06/17 16:55, Andy Shevchenko wrote:
> > On Fri, Jun 2, 2017 at 5:58 PM, Colin King <colin.king@canonical.com> wrote:
> >> The current comparison of entry < 0 will never be true since entry is an
> >> unsigned integer. Cast entry to an int to ensure -ve error return values
> >> from the call to jumbo_frm are correctly being caught.
> >
> >>         if (unlikely(is_jumbo) && likely(priv->synopsys_id <
> >>                                          DWMAC_CORE_4_00)) {
> >>                 entry = priv->hw->mode->jumbo_frm(tx_q, skb, csum_insertion);
> >> -               if (unlikely(entry < 0))
> >> +               if (unlikely((int)entry < 0))
> >
> > It feels like a hiding some other issue.
> >
>
> The alternative is:
>
> 		int rc = priv->hw->mode->jumbo_frm(tx_q, skb, csum_insertion);
> 		if (unlikely(rc < 0))
> 			goto dma_map_err;
>
> 		entry = rc;
>
> however, that is effectively the same. The cast I'm using is a well used
> idiom in the kernel, it used in almost a hundred similar cases.
>
> git grep "< 0" | grep "(int)" | wc -l
> 95

Does entry really have to be unsigned?  The jumbo_frm function returns an
int, not an unsigned int, so it seems unpleasant to make it unsigned
prematurely just to put a cast afterwards.  The remaining computation
seems to involve only small numbers.

julia

Re: [PATCH] net: stmmac: ensure jumbo_frm error return is correctly checked for -ve value

[Andy Shevchenko]

On Sat, Jun 3, 2017 at 7:35 PM, Colin Ian King <colin.king@canonical.com> wrote:
> On 03/06/17 16:55, Andy Shevchenko wrote:
>> On Fri, Jun 2, 2017 at 5:58 PM, Colin King <colin.king@canonical.com> wrote:
>>> The current comparison of entry < 0 will never be true since entry is an
>>> unsigned integer. Cast entry to an int to ensure -ve error return values
>>> from the call to jumbo_frm are correctly being caught.
>>
>>>         if (unlikely(is_jumbo) && likely(priv->synopsys_id <
>>>                                          DWMAC_CORE_4_00)) {
>>>                 entry = priv->hw->mode->jumbo_frm(tx_q, skb, csum_insertion);
>>> -               if (unlikely(entry < 0))
>>> +               if (unlikely((int)entry < 0))
>>
>> It feels like a hiding some other issue.
>>
>
> The alternative is:
>
>                 int rc = priv->hw->mode->jumbo_frm(tx_q, skb, csum_insertion);
>                 if (unlikely(rc < 0))
>                         goto dma_map_err;
>
>                 entry = rc;

Looks cleaner, though I was thinking about changing type of entry as
Julia suggested. Needs to be checked carefully anyway.

> however, that is effectively the same. The cast I'm using is a well used
> idiom in the kernel, it used in almost a hundred similar cases.

> git grep "< 0" | grep "(int)" | wc -l
> 95

With refined grep I'e got only 56 so far. And I see it's spread only
in 45 modules, most cases are single use cases.
So, I hardly can tell this is an idiom in kernel.

-- 
With Best Regards,
Andy Shevchenko

Re: [PATCH] net: stmmac: ensure jumbo_frm error return is correctly checked for -ve value

[Andy Shevchenko]

On Sat, Jun 3, 2017 at 7:35 PM, Colin Ian King <colin.king@canonical.com> wrote:
> On 03/06/17 16:55, Andy Shevchenko wrote:
>> On Fri, Jun 2, 2017 at 5:58 PM, Colin King <colin.king@canonical.com> wrote:
>>> The current comparison of entry < 0 will never be true since entry is an
>>> unsigned integer. Cast entry to an int to ensure -ve error return values
>>> from the call to jumbo_frm are correctly being caught.
>>
>>>         if (unlikely(is_jumbo) && likely(priv->synopsys_id <
>>>                                          DWMAC_CORE_4_00)) {
>>>                 entry = priv->hw->mode->jumbo_frm(tx_q, skb, csum_insertion);
>>> -               if (unlikely(entry < 0))
>>> +               if (unlikely((int)entry < 0))
>>
>> It feels like a hiding some other issue.
>>
>
> The alternative is:
>
>                 int rc = priv->hw->mode->jumbo_frm(tx_q, skb, csum_insertion);
>                 if (unlikely(rc < 0))
>                         goto dma_map_err;
>
>                 entry = rc;

Looks cleaner, though I was thinking about changing type of entry as
Julia suggested. Needs to be checked carefully anyway.

> however, that is effectively the same. The cast I'm using is a well used
> idiom in the kernel, it used in almost a hundred similar cases.

> git grep "< 0" | grep "(int)" | wc -l
> 95

With refined grep I'e got only 56 so far. And I see it's spread only
in 45 modules, most cases are single use cases.
So, I hardly can tell this is an idiom in kernel.

-- 
With Best Regards,
Andy Shevchenko

Re: [PATCH] net: stmmac: ensure jumbo_frm error return is correctly checked for -ve value

[David Miller]

From: Colin King <colin.king@canonical.com>
Date: Fri,  2 Jun 2017 15:58:27 +0100

> From: Colin Ian King <colin.king@canonical.com>
> 
> The current comparison of entry < 0 will never be true since entry is an
> unsigned integer. Cast entry to an int to ensure -ve error return values
> from the call to jumbo_frm are correctly being caught.
> 
> Detected by CoverityScan, CID#1238760 ("Macro compares unsigned to 0")
> 
> Signed-off-by: Colin Ian King <colin.king@canonical.com>

Like others have suggested, probably making 'entry' signed is
a better fix.

I was initially worried that STMMAC_GET_ENTRY() might become
more expensive if it was implemented using '%' but it is using
'and' masking instead which doesn't have that kind of problem.

Re: [PATCH] net: stmmac: ensure jumbo_frm error return is correctly checked for -ve value

[David Miller]

From: Colin King <colin.king@canonical.com>
Date: Fri,  2 Jun 2017 15:58:27 +0100

> From: Colin Ian King <colin.king@canonical.com>
> 
> The current comparison of entry < 0 will never be true since entry is an
> unsigned integer. Cast entry to an int to ensure -ve error return values
> from the call to jumbo_frm are correctly being caught.
> 
> Detected by CoverityScan, CID#1238760 ("Macro compares unsigned to 0")
> 
> Signed-off-by: Colin Ian King <colin.king@canonical.com>

Like others have suggested, probably making 'entry' signed is
a better fix.

I was initially worried that STMMAC_GET_ENTRY() might become
more expensive if it was implemented using '%' but it is using
'and' masking instead which doesn't have that kind of problem.