On Tue, Oct 17, 2023 at 03:51:58PM -0700, Jeff Johnson wrote:
> On 10/17/2023 2:12 PM, Justin Stitt wrote:
> > strncpy() is deprecated for use on NUL-terminated destination strings
> > [1] and as such we should prefer more robust and less ambiguous string
> > interfaces.
> >
> > `extra` is clearly supposed to be NUL-terminated which is evident by the
> > manual NUL-byte assignment as well as its immediate usage with strlen().
> >
> > Moreover, let's NUL-pad since there is deliberate effort (48 instances)
> > made elsewhere to zero-out buffers in these getters and setters:
> > 6050 | memset(local->config.nodeName, 0, sizeof(local->config.nodeName));
> > 6130 | memset(local->config.rates, 0, 8);
> > 6139 | memset(local->config.rates, 0, 8);
> > 6414 | memset(key.key, 0, MAX_KEY_SIZE);
> > 6497 | memset(extra, 0, 16);
> > (to be clear, strncpy also NUL-padded -- we are matching that behavior)
> >
> > Considering the above, a suitable replacement is `strscpy_pad` due to
> > the fact that it guarantees both NUL-termination and NUL-padding on the
> > destination buffer.
> >
> > Technically, we can now copy one less byte into `extra` as we cannot
> > determine the sizeof `extra` at compile time and the hard-coded value of
> > 16 means that strscpy_pad() will automatically truncate and set the byte
> > at offset 15 to NUL. However, the current code manually sets a
> > NUL-byte at offset 16. If this is an issue, the solution is to change
> > the hard-coded magic number to 17 instead of 16. I didn't do this in
> > this patch because a hard-coded 17 seems bad (even more so than 16).
>
> this function is a wext handler. In wext-core.c we have:
> static const struct iw_ioctl_description standard_ioctl[] = {
> ...
> [IW_IOCTL_IDX(SIOCGIWNICKN)] = {
> .header_type = IW_HEADER_TYPE_POINT,
> .token_size = 1,
> .max_tokens = IW_ESSID_MAX_SIZE,
> },
>
> So the buffer size is (strangely) IW_ESSID_MAX_SIZE if you want to use that
> for the buffer size
Yeah, that seems like a good refactor to do at the same time.
> > - strncpy(extra, local->config.nodeName, 16);
> > - extra[16] = '\0';
> > + strscpy_pad(extra, local->config.nodeName, 16);
Justin, can you respin this with the open-coded "16" updated?
-Kees
--
Kees Cook
