On Wed, Oct 18, 2023 at 5:03 PM Kees Cook <keescook@xxxxxxxxxxxx> wrote:
>
> On Tue, Oct 17, 2023 at 08:11:29PM +0000, Justin Stitt wrote:
> > Let's move away from using strncpy and instead use the more obvious
> > interface for this context.
> >
> > For wlc->pub->srom_ccode, we're just copying two bytes from ccode into
> > wlc->pub->srom_ccode with no expectation that srom_ccode be
> > NUL-terminated:
> > wlc->pub->srom_ccode is only used in regulatory_hint():
> > 1193 | if (wl->pub->srom_ccode[0] &&
> > 1194 | regulatory_hint(wl->wiphy, wl->pub->srom_ccode))
> > 1195 | wiphy_err(wl->wiphy, "%s: regulatory hint failed\n", __func__);
> >
> > We can see that only index 0 and index 1 are accessed.
> > 3307 | int regulatory_hint(struct wiphy *wiphy, const char *alpha2)
> > 3308 | {
> > ... | ...
> > 3322 | request->alpha2[0] = alpha2[0];
> > 3323 | request->alpha2[1] = alpha2[1];
> > ... | ...
> > 3332 | }
> >
> > Since this is just a simple byte copy with correct lengths, let's use
> > memcpy(). There should be no functional change.
> >
> > In a similar boat, both wlc->country_default and
> > wlc->autocountry_default are just simple byte copies so let's use
> > memcpy. However, FWICT they aren't used anywhere. (they should be
> > used or removed -- not in scope of my patch, though).
> >
> > Signed-off-by: Justin Stitt <justinstitt@xxxxxxxxxx>
> > ---
> > drivers/net/wireless/broadcom/brcm80211/brcmsmac/channel.c | 6 +++---
> > 1 file changed, 3 insertions(+), 3 deletions(-)
> >
> > diff --git a/drivers/net/wireless/broadcom/brcm80211/brcmsmac/channel.c b/drivers/net/wireless/broadcom/brcm80211/brcmsmac/channel.c
> > index 5a6d9c86552a..f6962e558d7c 100644
> > --- a/drivers/net/wireless/broadcom/brcm80211/brcmsmac/channel.c
> > +++ b/drivers/net/wireless/broadcom/brcm80211/brcmsmac/channel.c
> > @@ -341,7 +341,7 @@ struct brcms_cm_info *brcms_c_channel_mgr_attach(struct brcms_c_info *wlc)
> > /* store the country code for passing up as a regulatory hint */
> > wlc_cm->world_regd = brcms_world_regd(ccode, ccode_len);
> > if (brcms_c_country_valid(ccode))
> > - strncpy(wlc->pub->srom_ccode, ccode, ccode_len);
> > + memcpy(wlc->pub->srom_ccode, ccode, ccode_len);
>
> const char *ccode = sprom->alpha2;
> int ccode_len = sizeof(sprom->alpha2);
>
> struct ssb_sprom {
> ...
> char alpha2[2]; /* Country Code as two chars like EU or US */
>
> This should be marked __nonstring, IMO.
>
> struct brcms_pub {
> ...
> char srom_ccode[BRCM_CNTRY_BUF_SZ]; /* Country Code in SROM */
>
> #define BRCM_CNTRY_BUF_SZ 4 /* Country string is 3 bytes + NUL */
>
> This, however, is shown as explicitly %NUL terminated.
>
> The old strncpy wasn't %NUL terminating wlc->pub->srom_ccode, though, so
> the memcpy is the same result, but is that actually _correct_ here?
Judging from the usage, we can see that only bytes at offset 0 and 1 are
used. I think the comment "/* Country string is 3 bytes + NUL */" might
be misleading or perhaps there are other uses that I can't find (which
require NUL-termination)?
>
> >
> > /*
> > * If no custom world domain is found in the SROM, use the
> > @@ -354,10 +354,10 @@ struct brcms_cm_info *brcms_c_channel_mgr_attach(struct brcms_c_info *wlc)
> > }
> >
> > /* save default country for exiting 11d regulatory mode */
> > - strncpy(wlc->country_default, ccode, ccode_len);
> > + memcpy(wlc->country_default, ccode, ccode_len);
> >
> > /* initialize autocountry_default to driver default */
> > - strncpy(wlc->autocountry_default, ccode, ccode_len);
> > + memcpy(wlc->autocountry_default, ccode, ccode_len);
>
> struct brcms_c_info {
> ...
> char country_default[BRCM_CNTRY_BUF_SZ];
> char autocountry_default[BRCM_CNTRY_BUF_SZ];
>
> These are similar...
I can't find any uses for these either.
>
> So, this change results in the same behavior, but is it right?
>
> -Kees
>
> --
> Kees Cook
Thanks
Justin
