Re: [musl] [PATCH] fix segfault in lutimes when tv argument is NULL

["Érico Nogueira" <ericonr@disroot.org>]

On Thu Nov 12, 2020 at 5:32 PM -03, Markus Wichmann wrote:
> On Thu, Nov 12, 2020 at 03:43:27PM -0300, Érico Nogueira wrote:
> > From: Érico Rolim <ericonr@disroot.org>
> >
> > calling lutimes with tv=0 is valid if the applications wants to set the
> > timestamps to the current time. short-circuit the function to call
> > utimensat with times=0 directly if tv == 0.
> > ---
> >
> > Bug reported on IRC by nmeum
> >
> >  src/legacy/lutimes.c | 1 +
> >  1 file changed, 1 insertion(+)
> >
> > diff --git a/src/legacy/lutimes.c b/src/legacy/lutimes.c
> > index 2e5502d1..22176230 100644
> > --- a/src/legacy/lutimes.c
> > +++ b/src/legacy/lutimes.c
> > @@ -5,6 +5,7 @@
> >
> >  int lutimes(const char *filename, const struct timeval tv[2])
> >  {
> > +	if (!tv) return utimensat(AT_FDCWD, filename, 0, AT_SYMLINK_NOFOLLOW);
> >  	struct timespec times[2];
> >  	times[0].tv_sec  = tv[0].tv_sec;
> >  	times[0].tv_nsec = tv[0].tv_usec * 1000;
> > --
> > 2.29.2
> >
>
> Deja vu. We had a similar discussion in early March. The most recent
> e-mail in that thread stated that the patch "might be correct as-is."
> Though that patch did attempt to filter out invalid inputs as well. I
> had pointed out that the only spec available for lutimes does state that
> it should act like utimes(), and utimes() does allow for NULL inputs,
> but there was no reply. And no follow-up from the OP, either.
>
> Ciao,
> Markus

For reference, that thread starts at
https://www.openwall.com/lists/musl/2020/03/01/1

I based myself off of the futime() implementation, so both functions
have basically the same look / control flow now (except that futimes()
has the `struct timespec times[2]` declaration before the null check,
which I can fix in a v2, if necessary). Since it's a legacy function, I
didn't think it would be necessary to complicate matters further.

Re. checking the input values beyond a NULL check, futime() currently
doesn't do it, so for consistency's sake I think it would only make
sense to add that verification if it was added to futime() as well. That
said, I believe any verification should be left to utimensat(), which
seems to be called by most functions in the utimes family.

Cheers,
Érico