Re: Coverity: wilc_parse_join_bss_param(): Memory - illegal accesses

[Kees Cook <keescook@chromium.org>]

On Tue, Nov 05, 2019 at 06:11:03AM +0000, Ajay.Kathat@microchip.com wrote:
> 
> 
> On 04-Nov-19 11:08 PM, coverity-bot wrote:
> > External E-Mail
> > 
> > 
> > Hello!
> > 
> > This is an experimental automated report about issues detected by Coverity
> > from a scan of next-20191031 as part of the linux-next weekly scan project:
> > https://scan.coverity.com/projects/linux-next-weekly-scan
> > 
> > You're getting this email because you were associated with the identified
> > lines of code (noted below) that were touched by recent commits:
> > 
> > 4e0b0f42c9c7 ("staging: wilc1000: use struct to pack join parameters for FW")
> > 
> > Coverity reported the following:
> > 
> > *** CID 1487400:  Memory - illegal accesses  (OVERRUN)
> > /drivers/staging/wilc1000/wilc_hif.c: 496 in wilc_parse_join_bss_param()
> > 490     	if (supp_rates_ie) {
> > 491     		if (supp_rates_ie[1] > (WILC_MAX_RATES_SUPPORTED - rates_len))
> > 492     			param->supp_rates[0] = WILC_MAX_RATES_SUPPORTED;
> > 493     		else
> > 494     			param->supp_rates[0] += supp_rates_ie[1];
> > 495
> > vvv     CID 1487400:  Memory - illegal accesses  (OVERRUN)
> > vvv     Overrunning array of 13 bytes at byte offset 13 by dereferencing pointer "&param->supp_rates[rates_len + 1]". [Note: The source code implementation of the function has been overridden by a builtin model.]
> > 496     		memcpy(&param->supp_rates[rates_len + 1], supp_rates_ie + 2,
> > 497     		       (param->supp_rates[0] - rates_len));
> 
> As I understand, Ideally this condition should never arise because the
> maximum number of supported *basic rates* is up to 8 so the value of
> ‘rate_len’ will always be less then WILC_MAX_RATES_SUPPPRTED (i.e 12).
> Therefore '&param->supp_rates[rates_len+ 1]' will never try to access
> the 13 bytes in the array.
> But for the safer side, if need I can create a patch to block the
> addition of extended supported rates in ‘param->supp_rates’ array if
> ‘rates_len’ is 12 (i.e 'param->supp_rates' array is full after filing
> the basic supported rates).

I don't know the code myself, but generally speaking, it's best to
validate any assumptions like this. I'd say add a patch for it, since it
sounds pretty straight-forward to test.

-Kees

> 
> > 498     	}
> > 499
> > 500     	ht_ie = cfg80211_find_ie(WLAN_EID_HT_CAPABILITY, ies->data, ies->len);
> > 501     	if (ht_ie)
> > 
> > If this is a false positive, please let us know so we can mark it as
> > such, or teach the Coverity rules to be smarter. If not, please make
> > sure fixes get into linux-next. :) For patches fixing this, please
> > include these lines (but double-check the "Fixes" first):
> > 
> > Reported-by: coverity-bot <keescook+coverity-bot@chromium.org>
> > Addresses-Coverity-ID: 1487400 ("Memory - illegal accesses")
> > Fixes: 4e0b0f42c9c7 ("staging: wilc1000: use struct to pack join parameters for FW")
> > 
> > 
> > Thanks for your attention!
> > 

-- 
Kees Cook