[PATCH] gve: Fix a possible invalid memory access

[PATCH] gve: Fix a possible invalid memory access

[Christophe JAILLET]

It is spurious to allocate a bitmap for 'num_qpls' bits and record the
size of this bitmap with another value.

'qpl_map_size' is used in 'drivers/net/ethernet/google/gve/gve.h' with
'find_[first|next]_zero_bit()'.
So, it looks that memory after the allocated 'qpl_id_map' could be
scanned.

Remove the '* BITS_PER_BYTE' to have allocation and length be the same.

Fixes: f5cedc84a30d ("gve: Add transmit and receive support")
Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
---
This patch is completely speculative and un-tested!
You'll be warned.
---
 drivers/net/ethernet/google/gve/gve_main.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/net/ethernet/google/gve/gve_main.c b/drivers/net/ethernet/google/gve/gve_main.c
index 7647cd05b1d2..19fe9e9b62f5 100644
--- a/drivers/net/ethernet/google/gve/gve_main.c
+++ b/drivers/net/ethernet/google/gve/gve_main.c
@@ -866,7 +866,7 @@ static int gve_alloc_qpls(struct gve_priv *priv)
 	}
 
 	priv->qpl_cfg.qpl_map_size = BITS_TO_LONGS(num_qpls) *
-				     sizeof(unsigned long) * BITS_PER_BYTE;
+				     sizeof(unsigned long);
 	priv->qpl_cfg.qpl_id_map = kvcalloc(BITS_TO_LONGS(num_qpls),
 					    sizeof(unsigned long), GFP_KERNEL);
 	if (!priv->qpl_cfg.qpl_id_map) {
-- 
2.30.2

Re: [PATCH] gve: Fix a possible invalid memory access

[Willem de Bruijn]

On Sun, Oct 24, 2021 at 7:52 AM Christophe JAILLET
<christophe.jaillet@wanadoo.fr> wrote:
>
> It is spurious to allocate a bitmap for 'num_qpls' bits and record the
> size of this bitmap with another value.
>
> 'qpl_map_size' is used in 'drivers/net/ethernet/google/gve/gve.h' with
> 'find_[first|next]_zero_bit()'.
> So, it looks that memory after the allocated 'qpl_id_map' could be
> scanned.

find_first_zero_bit takes a length argument in bits:

    /**
     * find_first_zero_bit - find the first cleared bit in a memory region
     * @addr: The address to start the search at
     * @size: The maximum number of bits to search

qpl_map_size is passed to find_first_zero_bit.

It does seem roundabout to compute first the number of longs needed to
hold num_qpl bits

    BITS_TO_LONGS(num_qpls)

then again compute the number of bits in this buffer

    * sizeof(unsigned long) * BITS_PER_BYTE

Which will simply be num_qpls again.

But, removing BITS_PER_BYTE does not arrive at the right number.


>
> Remove the '* BITS_PER_BYTE' to have allocation and length be the same.
>
> Fixes: f5cedc84a30d ("gve: Add transmit and receive support")
> Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
> ---
> This patch is completely speculative and un-tested!
> You'll be warned.
> ---
>  drivers/net/ethernet/google/gve/gve_main.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/net/ethernet/google/gve/gve_main.c b/drivers/net/ethernet/google/gve/gve_main.c
> index 7647cd05b1d2..19fe9e9b62f5 100644
> --- a/drivers/net/ethernet/google/gve/gve_main.c
> +++ b/drivers/net/ethernet/google/gve/gve_main.c
> @@ -866,7 +866,7 @@ static int gve_alloc_qpls(struct gve_priv *priv)
>         }
>
>         priv->qpl_cfg.qpl_map_size = BITS_TO_LONGS(num_qpls) *
> -                                    sizeof(unsigned long) * BITS_PER_BYTE;
> +                                    sizeof(unsigned long);
>         priv->qpl_cfg.qpl_id_map = kvcalloc(BITS_TO_LONGS(num_qpls),
>                                             sizeof(unsigned long), GFP_KERNEL);
>         if (!priv->qpl_cfg.qpl_id_map) {
> --
> 2.30.2
>

Re: [PATCH] gve: Fix a possible invalid memory access

[Christophe JAILLET]

Le 24/10/2021 à 15:51, Willem de Bruijn a écrit :
> On Sun, Oct 24, 2021 at 7:52 AM Christophe JAILLET
> <christophe.jaillet@wanadoo.fr> wrote:
>>
>> It is spurious to allocate a bitmap for 'num_qpls' bits and record the
>> size of this bitmap with another value.
>>
>> 'qpl_map_size' is used in 'drivers/net/ethernet/google/gve/gve.h' with
>> 'find_[first|next]_zero_bit()'.
>> So, it looks that memory after the allocated 'qpl_id_map' could be
>> scanned.
> 
> find_first_zero_bit takes a length argument in bits:
> 
>      /**
>       * find_first_zero_bit - find the first cleared bit in a memory region
>       * @addr: The address to start the search at
>       * @size: The maximum number of bits to search
> 
> qpl_map_size is passed to find_first_zero_bit.
> 
> It does seem roundabout to compute first the number of longs needed to
> hold num_qpl bits
> 
>      BITS_TO_LONGS(num_qpls)
> 
> then again compute the number of bits in this buffer
> 
>      * sizeof(unsigned long) * BITS_PER_BYTE
> 
> Which will simply be num_qpls again.
> 
> But, removing BITS_PER_BYTE does not arrive at the right number.

(* embarrassed *)

So obvious.
Thank you for taking time for the explanation on a so badly broken patch.

I apologize for the noise and the waste of time :(


BTW, why not just have 'priv->qpl_cfg.qpl_map_size = num_qpls;'?

CJ

> 
> 
>>
>> Remove the '* BITS_PER_BYTE' to have allocation and length be the same.
>>
>> Fixes: f5cedc84a30d ("gve: Add transmit and receive support")
>> Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
>> ---
>> This patch is completely speculative and un-tested!
>> You'll be warned.
>> ---
>>   drivers/net/ethernet/google/gve/gve_main.c | 2 +-
>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/drivers/net/ethernet/google/gve/gve_main.c b/drivers/net/ethernet/google/gve/gve_main.c
>> index 7647cd05b1d2..19fe9e9b62f5 100644
>> --- a/drivers/net/ethernet/google/gve/gve_main.c
>> +++ b/drivers/net/ethernet/google/gve/gve_main.c
>> @@ -866,7 +866,7 @@ static int gve_alloc_qpls(struct gve_priv *priv)
>>          }
>>
>>          priv->qpl_cfg.qpl_map_size = BITS_TO_LONGS(num_qpls) *
>> -                                    sizeof(unsigned long) * BITS_PER_BYTE;
>> +                                    sizeof(unsigned long);
>>          priv->qpl_cfg.qpl_id_map = kvcalloc(BITS_TO_LONGS(num_qpls),
>>                                              sizeof(unsigned long), GFP_KERNEL);
>>          if (!priv->qpl_cfg.qpl_id_map) {
>> --
>> 2.30.2
>>
> 

Re: [PATCH] gve: Fix a possible invalid memory access

[Willem de Bruijn]

On Sun, Oct 24, 2021 at 10:58 AM Christophe JAILLET
<christophe.jaillet@wanadoo.fr> wrote:
>
> Le 24/10/2021 à 15:51, Willem de Bruijn a écrit :
> > On Sun, Oct 24, 2021 at 7:52 AM Christophe JAILLET
> > <christophe.jaillet@wanadoo.fr> wrote:
> >>
> >> It is spurious to allocate a bitmap for 'num_qpls' bits and record the
> >> size of this bitmap with another value.
> >>
> >> 'qpl_map_size' is used in 'drivers/net/ethernet/google/gve/gve.h' with
> >> 'find_[first|next]_zero_bit()'.
> >> So, it looks that memory after the allocated 'qpl_id_map' could be
> >> scanned.
> >
> > find_first_zero_bit takes a length argument in bits:
> >
> >      /**
> >       * find_first_zero_bit - find the first cleared bit in a memory region
> >       * @addr: The address to start the search at
> >       * @size: The maximum number of bits to search
> >
> > qpl_map_size is passed to find_first_zero_bit.
> >
> > It does seem roundabout to compute first the number of longs needed to
> > hold num_qpl bits
> >
> >      BITS_TO_LONGS(num_qpls)
> >
> > then again compute the number of bits in this buffer
> >
> >      * sizeof(unsigned long) * BITS_PER_BYTE
> >
> > Which will simply be num_qpls again.
> >
> > But, removing BITS_PER_BYTE does not arrive at the right number.
>
> (* embarrassed *)
>
> So obvious.
> Thank you for taking time for the explanation on a so badly broken patch.
>
> I apologize for the noise and the waste of time :(

No worries, it happens. Thanks for reviewing code.

>
> BTW, why not just have 'priv->qpl_cfg.qpl_map_size = num_qpls;'?

Yes, that seems more straightforward to me too.