linux-kernel - Re: [PATCH] staging: rtl8188eu: Fix off-by-one in core/rtw_mlme

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Date:   Tue, 27 Nov 2018 11:15:42 +0300
From:   Dan Carpenter <dan.carpenter@...cle.com>
To:     Yang Xiao <YangX92@...mail.com>
Cc:     "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
        "r.weclawski@...il.com" <r.weclawski@...il.com>,
        "straube.linux@...il.com" <straube.linux@...il.com>,
        "santhameena13@...il.com" <santhameena13@...il.com>,
        "devel@...verdev.osuosl.org" <devel@...verdev.osuosl.org>,
        "jananis37@...il.com" <jananis37@...il.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] staging: rtl8188eu: Fix off-by-one in core/rtw_mlme_ext.c

The original code is OK.

On Tue, Nov 27, 2018 at 07:29:07AM +0000, Yang Xiao wrote:
> From: Young_X <YangX92@...mail.com>
> 
>     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@...mail.com>
> ---
>  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