On Wed, Jul 05, 2017 at 07:12:28PM -0400, Ted Unangst wrote:
> Olivier Antoine wrote:
> > Hi all,
> >
> > Recently a bug has been identified in Tor:
> >
> > https://trac.torproject.org/projects/tor/ticket/22789
> >
> > As comments were made, questions were raised about the use of strtol(3),
> > the different interpretations of the standard and their implementation.
> >
> > To summarize, the question revolves around the processing of strings in
> > base=16 and with the optional prefix '0x'.
> >
> > l = strtol ("0xquux", & rest, 16);
> >
> > Produce
> > l=0 rest=0xquux on OpenBSD
> > l=0 rest=xquux on Linux
> >
> > Do specialists of the standard or developers have an opinion on this point
> > of detail?
> > Is there a defined behavior?
>
> My opinion is that well written code would avoid feeding ambigious strings to
> strtol. Today's it's 0xquux and tomorrow it's 0xaquux and now you have a
> problem.
>
> But, let's read
> http://pubs.opengroup.org/onlinepubs/9699919799/functions/strtol.html
>
> It's actually unclear IMO. But I don't see anything prohibiting interpreting
> the string as an optional prefix with an empty body.
Well:
The functionality described on this reference page is aligned with the ISO C
standard. Any conflict between the requirements described here and the ISO C
standard is unintentional. This volume of POSIX.1-2008 defers to the ISO C
standard.
This is Sparta^WISO C we're talking about. The wording of posix is actually
irrelevant.
ISO C 99 is waaays clearer.
7.20.1.4 (3) If the value of base is zero, the expected form of the subject
sequence is that of an integer constant *as described in 6.4.4.1*, optionally
preceded by a plus or minus sign but not including an integer suffix [...]
7.20.1.4 (4) The subject sequence is defined as the longest intial subsequence
of the input string [...] *that is of the expected form*.
6.4.4.1 is a grammar
integer-constant:
[...]
hexadecimal-constant integer-suffix_opt
hexadecimal-constant:
hexadecimal-prefix hexadecimal-digit
hexadecimal-constant hexadecimal-digit
There is no wiggle room there.
That grammar is explicit that there must be at least one hexadecimal digit
after the prefix.
