[PATCH] iwlwifi: d3: use struct_size() in kzalloc()

[PATCH] iwlwifi: d3: use struct_size() in kzalloc()

[Gustavo A. R. Silva]

One of the more common cases of allocation size calculations is finding
the size of a structure that has a zero-sized array at the end, along
with memory for some number of elements for that array. For example:

struct foo {
	int stuff;
        void *entry[];
};

instance = kzalloc(sizeof(struct foo) + sizeof(void *) * count, GFP_KERNEL);

Instead of leaving these open-coded and prone to type mistakes, we can
now use the new struct_size() helper:

instance = kzalloc(struct_size(instance, entry, count), GFP_KERNEL);

This issue was detected with the help of Coccinelle.

Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>
---
 drivers/net/wireless/intel/iwlwifi/mvm/d3.c | 6 ++----
 1 file changed, 2 insertions(+), 4 deletions(-)

diff --git a/drivers/net/wireless/intel/iwlwifi/mvm/d3.c b/drivers/net/wireless/intel/iwlwifi/mvm/d3.c
index 79bdae9..6960318 100644
--- a/drivers/net/wireless/intel/iwlwifi/mvm/d3.c
+++ b/drivers/net/wireless/intel/iwlwifi/mvm/d3.c
@@ -1769,8 +1769,7 @@ static void iwl_mvm_query_netdetect_reasons(struct iwl_mvm *mvm,
 		n_matches = 0;
 	}
 
-	net_detect = kzalloc(sizeof(*net_detect) +
-			     (n_matches * sizeof(net_detect->matches[0])),
+	net_detect = kzalloc(struct_size(net_detect, matches, n_matches),
 			     GFP_KERNEL);
 	if (!net_detect || !n_matches)
 		goto out_report_nd;
@@ -1785,8 +1784,7 @@ static void iwl_mvm_query_netdetect_reasons(struct iwl_mvm *mvm,
 		for (j = 0; j < SCAN_OFFLOAD_MATCHING_CHANNELS_LEN; j++)
 			n_channels += hweight8(fw_match->matching_channels[j]);
 
-		match = kzalloc(sizeof(*match) +
-				(n_channels * sizeof(*match->channels)),
+		match = kzalloc(struct_size(match, channels, n_channels),
 				GFP_KERNEL);
 		if (!match)
 			goto out_report_nd;
-- 
2.7.4

Re: [PATCH] iwlwifi: d3: use struct_size() in kzalloc()

[Kees Cook]

On Thu, Aug 23, 2018 at 6:15 PM, Gustavo A. R. Silva
<gustavo@embeddedor.com> wrote:
> One of the more common cases of allocation size calculations is finding
> the size of a structure that has a zero-sized array at the end, along
> with memory for some number of elements for that array. For example:
>
> struct foo {
>         int stuff;
>         void *entry[];
> };
>
> instance = kzalloc(sizeof(struct foo) + sizeof(void *) * count, GFP_KERNEL);
>
> Instead of leaving these open-coded and prone to type mistakes, we can
> now use the new struct_size() helper:
>
> instance = kzalloc(struct_size(instance, entry, count), GFP_KERNEL);
>
> This issue was detected with the help of Coccinelle.
>
> Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>

Reviewed-by: Kees Cook <keescook@chromium.org>

-Kees

> ---
>  drivers/net/wireless/intel/iwlwifi/mvm/d3.c | 6 ++----
>  1 file changed, 2 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/net/wireless/intel/iwlwifi/mvm/d3.c b/drivers/net/wireless/intel/iwlwifi/mvm/d3.c
> index 79bdae9..6960318 100644
> --- a/drivers/net/wireless/intel/iwlwifi/mvm/d3.c
> +++ b/drivers/net/wireless/intel/iwlwifi/mvm/d3.c
> @@ -1769,8 +1769,7 @@ static void iwl_mvm_query_netdetect_reasons(struct iwl_mvm *mvm,
>                 n_matches = 0;
>         }
>
> -       net_detect = kzalloc(sizeof(*net_detect) +
> -                            (n_matches * sizeof(net_detect->matches[0])),
> +       net_detect = kzalloc(struct_size(net_detect, matches, n_matches),
>                              GFP_KERNEL);
>         if (!net_detect || !n_matches)
>                 goto out_report_nd;
> @@ -1785,8 +1784,7 @@ static void iwl_mvm_query_netdetect_reasons(struct iwl_mvm *mvm,
>                 for (j = 0; j < SCAN_OFFLOAD_MATCHING_CHANNELS_LEN; j++)
>                         n_channels += hweight8(fw_match->matching_channels[j]);
>
> -               match = kzalloc(sizeof(*match) +
> -                               (n_channels * sizeof(*match->channels)),
> +               match = kzalloc(struct_size(match, channels, n_channels),
>                                 GFP_KERNEL);
>                 if (!match)
>                         goto out_report_nd;
> --
> 2.7.4
>



-- 
Kees Cook
Pixel Security

Re: [PATCH] iwlwifi: d3: use struct_size() in kzalloc()

[Joe Perches]

On Thu, 2018-08-23 at 20:03 -0700, Kees Cook wrote:
> On Thu, Aug 23, 2018 at 6:15 PM, Gustavo A. R. Silva
> <gustavo@embeddedor.com> wrote:
> > One of the more common cases of allocation size calculations is finding
> > the size of a structure that has a zero-sized array at the end, along
> > with memory for some number of elements for that array. For example:
> > 
> > struct foo {
> >         int stuff;
> >         void *entry[];
> > };

Question for Gustavo.

Did you find any existing instances that are miscalculated?

I believe there are some cases like:

	size = sizeof(struct foo) + count * sizeof(something);
	ptr = kmalloc(size);
	memset(ptr + sizeof(struct foo), 0, size - sizeof(struct foo));

where something could go wrong and not be detected.

Re: [PATCH] iwlwifi: d3: use struct_size() in kzalloc()

[Gustavo A. R. Silva]

Hi Joe,

On 8/23/18 11:33 PM, Joe Perches wrote:
> On Thu, 2018-08-23 at 20:03 -0700, Kees Cook wrote:
>> On Thu, Aug 23, 2018 at 6:15 PM, Gustavo A. R. Silva
>> <gustavo@embeddedor.com> wrote:
>>> One of the more common cases of allocation size calculations is finding
>>> the size of a structure that has a zero-sized array at the end, along
>>> with memory for some number of elements for that array. For example:
>>>
>>> struct foo {
>>>         int stuff;
>>>         void *entry[];
>>> };
> 
> Question for Gustavo.
> 
> Did you find any existing instances that are miscalculated?
> 

I found the following bug:

https://lore.kernel.org/patchwork/patch/977357/


> I believe there are some cases like:
> 
> 	size = sizeof(struct foo) + count * sizeof(something);
> 	ptr = kmalloc(size);
> 	memset(ptr + sizeof(struct foo), 0, size - sizeof(struct foo));
> 
> where something could go wrong and not be detected.
> 

It might be worth it to write a Coccinelle script for this.

--
Gustavo

Re: [PATCH] iwlwifi: d3: use struct_size() in kzalloc()

[Luciano Coelho]

On Thu, 2018-08-23 at 20:15 -0500, Gustavo A. R. Silva wrote:
> One of the more common cases of allocation size calculations is finding
> the size of a structure that has a zero-sized array at the end, along
> with memory for some number of elements for that array. For example:
> 
> struct foo {
> 	int stuff;
>         void *entry[];
> };
> 
> instance = kzalloc(sizeof(struct foo) + sizeof(void *) * count, GFP_KERNEL);
> 
> Instead of leaving these open-coded and prone to type mistakes, we can
> now use the new struct_size() helper:
> 
> instance = kzalloc(struct_size(instance, entry, count), GFP_KERNEL);
> 
> This issue was detected with the help of Coccinelle.
> 
> Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>
> ---
>  drivers/net/wireless/intel/iwlwifi/mvm/d3.c | 6 ++----
>  1 file changed, 2 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/net/wireless/intel/iwlwifi/mvm/d3.c b/drivers/net/wireless/intel/iwlwifi/mvm/d3.c
> index 79bdae9..6960318 100644
> --- a/drivers/net/wireless/intel/iwlwifi/mvm/d3.c
> +++ b/drivers/net/wireless/intel/iwlwifi/mvm/d3.c
> @@ -1769,8 +1769,7 @@ static void iwl_mvm_query_netdetect_reasons(struct iwl_mvm *mvm,
>  		n_matches = 0;
>  	}
>  
> -	net_detect = kzalloc(sizeof(*net_detect) +
> -			     (n_matches * sizeof(net_detect->matches[0])),
> +	net_detect = kzalloc(struct_size(net_detect, matches, n_matches),
>  			     GFP_KERNEL);
>  	if (!net_detect || !n_matches)
>  		goto out_report_nd;
> @@ -1785,8 +1784,7 @@ static void iwl_mvm_query_netdetect_reasons(struct iwl_mvm *mvm,
>  		for (j = 0; j < SCAN_OFFLOAD_MATCHING_CHANNELS_LEN; j++)
>  			n_channels += hweight8(fw_match->matching_channels[j]);
>  
> -		match = kzalloc(sizeof(*match) +
> -				(n_channels * sizeof(*match->channels)),
> +		match = kzalloc(struct_size(match, channels, n_channels),
>  				GFP_KERNEL);
>  		if (!match)
>  			goto out_report_nd;

Thanks! I applied this to our internal tree and it will reach the
mainline following our normal process.

--
Cheers,
Luca.