[PATCH] misc: tifm: Remove VLA

[PATCH] misc: tifm: Remove VLA

[Laura Abbott]

There's an ongoing effort to remove VLAs[1] from the kernel to eventually
turn on -Wvla. The single VLA can either take a value of 2 or 4 so switch
to the upper bound.

[1] https://lkml.org/lkml/2018/3/7/621

Signed-off-by: Laura Abbott <labbott@redhat.com>
---
 drivers/misc/tifm_7xx1.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/misc/tifm_7xx1.c b/drivers/misc/tifm_7xx1.c
index e5f108713dd8..690eaaea5ce4 100644
--- a/drivers/misc/tifm_7xx1.c
+++ b/drivers/misc/tifm_7xx1.c
@@ -239,7 +239,8 @@ static int tifm_7xx1_resume(struct pci_dev *dev)
 	unsigned long timeout;
 	unsigned int good_sockets = 0, bad_sockets = 0;
 	unsigned long flags;
-	unsigned char new_ids[fm->num_sockets];
+	/* Maximum number of entries is 4 */
+	unsigned char new_ids[4];
 	DECLARE_COMPLETION_ONSTACK(finish_resume);
 
 	pci_set_power_state(dev, PCI_D0);
-- 
2.14.3

Re: [PATCH] misc: tifm: Remove VLA

[Arnd Bergmann]

On Mon, Apr 9, 2018 at 11:07 PM, Laura Abbott <labbott@redhat.com> wrote:
> There's an ongoing effort to remove VLAs[1] from the kernel to eventually
> turn on -Wvla. The single VLA can either take a value of 2 or 4 so switch
> to the upper bound.
>
> [1] https://lkml.org/lkml/2018/3/7/621
>
> Signed-off-by: Laura Abbott <labbott@redhat.com>
> ---
>  drivers/misc/tifm_7xx1.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/misc/tifm_7xx1.c b/drivers/misc/tifm_7xx1.c
> index e5f108713dd8..690eaaea5ce4 100644
> --- a/drivers/misc/tifm_7xx1.c
> +++ b/drivers/misc/tifm_7xx1.c
> @@ -239,7 +239,8 @@ static int tifm_7xx1_resume(struct pci_dev *dev)
>         unsigned long timeout;
>         unsigned int good_sockets = 0, bad_sockets = 0;
>         unsigned long flags;
> -       unsigned char new_ids[fm->num_sockets];
> +       /* Maximum number of entries is 4 */
> +       unsigned char new_ids[4];
>         DECLARE_COMPLETION_ONSTACK(finish_resume);
>

I like the idea of removing all the VLAs, but this one appears to make
the code less robust rather than more: In case of an unexpected
fm->num_sockets value, we now not only overflow the kernel stack
area but also the local variable into the neighboring stack slots.

Maybe add an extra overflow check?

       Arnd

diff --git a/drivers/misc/tifm_7xx1.c b/drivers/misc/tifm_7xx1.c
index e5f108713dd8..c702cd92d396 100644
--- a/drivers/misc/tifm_7xx1.c
+++ b/drivers/misc/tifm_7xx1.c
@@ -239,9 +239,12 @@ static int tifm_7xx1_resume(struct pci_dev *dev)
        unsigned long timeout;
        unsigned int good_sockets = 0, bad_sockets = 0;
        unsigned long flags;
-       unsigned char new_ids[fm->num_sockets];
+      /* Maximum number of entries is 4 */
+       unsigned char new_ids[4];
        DECLARE_COMPLETION_ONSTACK(finish_resume);

+       if (WARN_ON(fm->num_sockets > ARRAY_SIZE(new_ids)))
+               return -ENXIO;
+
        pci_set_power_state(dev, PCI_D0);
        pci_restore_state(dev);
        rc = pci_enable_device(dev);

Re: [PATCH] misc: tifm: Remove VLA

[Laura Abbott]

On 04/10/2018 12:57 AM, Arnd Bergmann wrote:
> On Mon, Apr 9, 2018 at 11:07 PM, Laura Abbott <labbott@redhat.com> wrote:
>> There's an ongoing effort to remove VLAs[1] from the kernel to eventually
>> turn on -Wvla. The single VLA can either take a value of 2 or 4 so switch
>> to the upper bound.
>>
>> [1] https://lkml.org/lkml/2018/3/7/621
>>
>> Signed-off-by: Laura Abbott <labbott@redhat.com>
>> ---
>>   drivers/misc/tifm_7xx1.c | 3 ++-
>>   1 file changed, 2 insertions(+), 1 deletion(-)
>>
>> diff --git a/drivers/misc/tifm_7xx1.c b/drivers/misc/tifm_7xx1.c
>> index e5f108713dd8..690eaaea5ce4 100644
>> --- a/drivers/misc/tifm_7xx1.c
>> +++ b/drivers/misc/tifm_7xx1.c
>> @@ -239,7 +239,8 @@ static int tifm_7xx1_resume(struct pci_dev *dev)
>>          unsigned long timeout;
>>          unsigned int good_sockets = 0, bad_sockets = 0;
>>          unsigned long flags;
>> -       unsigned char new_ids[fm->num_sockets];
>> +       /* Maximum number of entries is 4 */
>> +       unsigned char new_ids[4];
>>          DECLARE_COMPLETION_ONSTACK(finish_resume);
>>
> 
> I like the idea of removing all the VLAs, but this one appears to make
> the code less robust rather than more: In case of an unexpected
> fm->num_sockets value, we now not only overflow the kernel stack
> area but also the local variable into the neighboring stack slots.
> 
> Maybe add an extra overflow check?
> 

Sure.

>         Arnd
> 
> diff --git a/drivers/misc/tifm_7xx1.c b/drivers/misc/tifm_7xx1.c
> index e5f108713dd8..c702cd92d396 100644
> --- a/drivers/misc/tifm_7xx1.c
> +++ b/drivers/misc/tifm_7xx1.c
> @@ -239,9 +239,12 @@ static int tifm_7xx1_resume(struct pci_dev *dev)
>          unsigned long timeout;
>          unsigned int good_sockets = 0, bad_sockets = 0;
>          unsigned long flags;
> -       unsigned char new_ids[fm->num_sockets];
> +      /* Maximum number of entries is 4 */
> +       unsigned char new_ids[4];
>          DECLARE_COMPLETION_ONSTACK(finish_resume);
> 
> +       if (WARN_ON(fm->num_sockets > ARRAY_SIZE(new_ids)))
> +               return -ENXIO;
> +
>          pci_set_power_state(dev, PCI_D0);
>          pci_restore_state(dev);
>          rc = pci_enable_device(dev);
>