Re: [PATCH] staging: rtl8712: Replace snprintf with scnprintf

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On Tue, Oct 01, 2019 at 11:09:26PM +0530, Rohit Sarkar wrote:
> On Tue, Oct 01, 2019 at 11:45:14AM +0300, Dan Carpenter wrote:
> > > diff --git a/drivers/staging/rtl8712/rtl871x_ioctl_linux.c b/drivers/staging/rtl8712/rtl871x_ioctl_linux.c
> > > index b08b9a191a34..ff5edcaba64d 100644
> > > --- a/drivers/staging/rtl8712/rtl871x_ioctl_linux.c
> > > +++ b/drivers/staging/rtl8712/rtl871x_ioctl_linux.c
> > > @@ -142,7 +142,7 @@ static noinline_for_stack char *translate_scan_wpa(struct iw_request_info *info,
> > >  		memset(buf, 0, MAX_WPA_IE_LEN);
> > >  		n = sprintf(buf, "wpa_ie=");
> > >  		for (i = 0; i < wpa_len; i++) {
> > > -			n += snprintf(buf + n, MAX_WPA_IE_LEN - n,
> > > +			n += scnprintf(buf + n, MAX_WPA_IE_LEN - n,
> > >  						"%02x", wpa_ie[i]);
> > >  			if (n >= MAX_WPA_IE_LEN)
> >                             ^^^^^^^^^^^^^^^^^^^
> > It checks for overflow here.  This check is impossible now and doesn't
> > make sense.  The other loop is similar.
> 
> Good catch! I must have overlooked this.
> "n" cannot be greater than MAX_WPA_IE_LEN but it can be equal to that
> value. We can replace the '>=' with '==' so that we don't loop
> unnecessarily when n has reached it's threshold.

No.  scnprintf() returns the number of characters *not counting the
NUL terminator*.  So it can be a maximum of MAX_WPA_IE_LEN - 1.

regards,
dan carpenter

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