Re: [PATCH] staging: rtl8188eu: Fix off-by-one in core/rtw_mlme_ext.c

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Hi,

See commit ef9209b642f ("staging: rtl8723bs: Fix indenting errors and an 
off-by-one mistake in core/rtw_mlme_ext.c") for detail.

I don't know how can you make sure that line 3254 can be true in the for 
loop.  If the condition never satisfies, then there is an off-by-one 
access in line 3267.

If you can prove it, then the patch is unnecessary.

Young

On 2018/11/27 16:15, Dan Carpenter wrote:
> The original code is OK.
>
> On Tue, Nov 27, 2018 at 07:29:07AM +0000, Yang Xiao wrote:
>> From: Young_X <YangX92@xxxxxxxxxxx>
>>
>>      The error at line 3267 was the result of an off-by-one error in
>>      a for loop in line 3253.
>>      If condition in line 3254 never satisfies, then the value of
>>      pstat->aid is NUM_STA+1. This will lead to out-of-bound access
>>      in line 3267.
> It's best to avoid line numbers in the commit message unless you paste
> the actual code, because sometimes people will be using different line
> numbers from you.
>
>> Signed-off-by: Young_X <YangX92@xxxxxxxxxxx>
>> ---
>>   drivers/staging/rtl8188eu/core/rtw_mlme_ext.c | 2 +-
>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/drivers/staging/rtl8188eu/core/rtw_mlme_ext.c b/drivers/staging/rtl8188eu/core/rtw_mlme_ext.c
>> index 6790b840..0854adc 100644
>> --- a/drivers/staging/rtl8188eu/core/rtw_mlme_ext.c
>> +++ b/drivers/staging/rtl8188eu/core/rtw_mlme_ext.c
>> @@ -3250,7 +3250,7 @@ static unsigned int OnAssocReq(struct adapter *padapter,
>>   	if (pstat->aid > 0) {
>>   		DBG_88E("  old AID %d\n", pstat->aid);
>>   	} else {
>> -		for (pstat->aid = 1; pstat->aid <= NUM_STA; pstat->aid++)
>> +		for (pstat->aid = 1; pstat->aid < NUM_STA; pstat->aid++)
> drivers/staging/rtl8188eu/core/rtw_mlme_ext.c
>    3249          /* get a unique AID */
>    3250          if (pstat->aid > 0) {
>    3251                  DBG_88E("  old AID %d\n", pstat->aid);
>    3252          } else {
>    3253                  for (pstat->aid = 1; pstat->aid <= NUM_STA; pstat->aid++)
>    3254                          if (pstapriv->sta_aid[pstat->aid - 1] == NULL)
>    3255                                  break;
>    3256
>    3257                  /* if (pstat->aid > NUM_STA) { */
>                             ^^^^^^^^^^^^^^^^^^^^^^^^
> This comment is key.  pstapriv->max_num_sta is always less than or equal
> to NUM_STA.
>
>    3258                  if (pstat->aid > pstapriv->max_num_sta) {
>    3259                          pstat->aid = 0;
>    3260
>    3261                          DBG_88E("  no room for more AIDs\n");
>    3262
>    3263                          status = WLAN_STATUS_AP_UNABLE_TO_HANDLE_NEW_STA;
>    3264
>    3265                          goto OnAssocReqFail;
>    3266                  } else {
>    3267                          pstapriv->sta_aid[pstat->aid - 1] = pstat;
>                                                    ^^^^^^^^^^^^^^
> So this is fine.
>
>    3268                          DBG_88E("allocate new AID=(%d)\n", pstat->aid);
>    3269                  }
>    3270          }
>    3271
>
> regards,
> dan carpenter
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