Re: [PATCH wireless] wifi: iwlwifi: mvm: Fix a memory corruption issue

[Greenman, Gregory]

On Sun, 2023-07-23 at 22:24 +0200, Christophe JAILLET wrote:
> A few lines above, space is kzalloc()'ed for:
>         sizeof(struct iwl_nvm_data) +
>         sizeof(struct ieee80211_channel) +
>         sizeof(struct ieee80211_rate)
> 
> 'mvm->nvm_data' is a 'struct iwl_nvm_data', so it is fine.
> 
> At the end of this structure, there is the 'channels' flex array.
> Each element is of type 'struct ieee80211_channel'.
> So only 1 element is allocated in this array.
> 
> When doing:
>   mvm->nvm_data->bands[0].channels = mvm->nvm_data->channels;
> We point at the first element of the 'channels' flex array.
> So this is fine.
> 
> However, when doing:
>   mvm->nvm_data->bands[0].bitrates =
>                         (void *)((u8 *)mvm->nvm_data->channels + 1);
> because of the "(u8 *)" cast, we add only 1 to the address of the beginning
> of the flex array.
> 
> It is likely that we want point at the 'struct ieee80211_rate' allocated
> just after.
> 
> Remove the spurious casting so that the pointer arithmetic works as
> expected.
> 
> Fixes: 8ca151b568b6 ("iwlwifi: add the MVM driver")
> Signed-off-by: Christophe JAILLET <christophe.jaillet@xxxxxxxxxx>
> ---
> I've checked in the .s files, and :
> 
> Before
> ======
> # drivers/net/wireless/intel/iwlwifi/mvm/fw.c:801:              mvm->nvm_data->bands[0].channels = mvm->nvm_data->channels;
>         leaq    1448(%r13), %rax        #, tmp248
> 
> # drivers/net/wireless/intel/iwlwifi/mvm/fw.c:805:                      (void *)((u8 *)mvm->nvm_data->channels + 1);
>         leaq    1449(%r13), %rax        #, tmp252
> 
> 
> After:
> =====
> # drivers/net/wireless/intel/iwlwifi/mvm/fw.c:801:              mvm->nvm_data->bands[0].channels = mvm->nvm_data->channels;
>         leaq    1448(%r13), %rax        #, tmp248
> 
> # drivers/net/wireless/intel/iwlwifi/mvm/fw.c:805:                      (void *)(mvm->nvm_data->channels + 1);
>         leaq    1512(%r13), %rax        #, tmp252
> 
> And on my system sizeof(struct ieee80211_channel) = 64
> 
> /!\ This patch is only speculative and untested. /!\
> 
> It is strange that a memory corruption issue has been un-noticed for more
> than 10 years.
> 
> So review with care.
> ---
>  drivers/net/wireless/intel/iwlwifi/mvm/fw.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/net/wireless/intel/iwlwifi/mvm/fw.c b/drivers/net/wireless/intel/iwlwifi/mvm/fw.c
> index 1f5db65a088d..1d5ee4330f29 100644
> --- a/drivers/net/wireless/intel/iwlwifi/mvm/fw.c
> +++ b/drivers/net/wireless/intel/iwlwifi/mvm/fw.c

> @@ -802,7 +802,7 @@ int iwl_run_init_mvm_ucode(struct iwl_mvm *mvm)
>                 mvm->nvm_data->bands[0].n_channels = 1;
>                 mvm->nvm_data->bands[0].n_bitrates = 1;
>                 mvm->nvm_data->bands[0].bitrates =
> -                       (void *)((u8 *)mvm->nvm_data->channels + 1);
> +                       (void *)(mvm->nvm_data->channels + 1);
>                 mvm->nvm_data->bands[0].bitrates->hw_value = 10;
>         }
>  
Acked-by: Gregory Greenman <gregory.greenman@xxxxxxxxx>