Re: Possible memory corruption (src/timezone/zic.c b/src/timezone/zic.c)

At Sat, 15 May 2021 11:35:13 -0300, Ranier Vilela <ranier.vf@gmail.com> wrote in
> Em sex., 14 de mai. de 2021 às 19:52, Tom Lane <tgl@sss.pgh.pa.us> escreveu:
>
> > I wrote:
> > > So the question for us is whether it's worth trying to make pgreadlink
> > > conform to the letter of the POSIX spec in this detail.  TBH, I can't
> > > get excited about that, at least not so far as zic's usage is concerned.
> >
> > Hmmm ... on closer inspection, though, it might not be that hard.
> > pgreadlink is already using a fixed-length buffer (with only enough
> > room for MAX_PATH WCHARs) for the input of WideCharToMultiByte.  So
> > it could use a fixed-length buffer of say 4 * MAX_PATH bytes for the
> > output, and then transfer just the appropriate amount of data to the
> > caller's buffer.
> >
> Following your directions, maybe something like this will solve?

-       DWORD           attr;
-       HANDLE          h;

Why the patch moves the definitions for "attr" and "h"?

+       Assert(path != NULL && buf != NULL);

I don't think it's required.  Even if we want to imitate readlink,
they should (maybe) return EFALUT in that case.

+       buf[r] = '\0';

readlink is defined as not appending a terminator.  In the first place
the "buf[r] = '\0'" is overrunning the given buffer.

-       return 0 <= readlink(name, &c, 1);
+       return 0 <= readlink(name, linkpath, sizeof(linkpath));

According to the discussion, we don't want to modify zic.c at
all. (Maybe forgot to remove?)