Re: [PATCH] time: strftime_l: Use malloc rather than an unbounded alloca.

[Joe Simmons-Talbott <josimmon@redhat.com>]

On Tue, May 16, 2023 at 04:28:58PM -0300, Adhemerval Zanella Netto wrote:
> 
> 
> On 10/05/23 16:59, Joe Simmons-Talbott via Libc-alpha wrote:
> > Avoid possible stack overflow by replacing alloca() with malloc().
> > ---
> >  time/strftime_l.c | 8 ++++++--
> >  1 file changed, 6 insertions(+), 2 deletions(-)
> > 
> > diff --git a/time/strftime_l.c b/time/strftime_l.c
> > index 402c6c4111..59d3e1a3b2 100644
> > --- a/time/strftime_l.c
> > +++ b/time/strftime_l.c
> > @@ -273,8 +273,9 @@ static const CHAR_T zeroes[16] = /* "0000000000000000" */
> >      const char *__s = os;						      \
> >      memset (&__st, '\0', sizeof (__st));				      \
> >      l = __mbsrtowcs_l (NULL, &__s, 0, &__st, loc);			      \
> > -    ws = alloca ((l + 1) * sizeof (wchar_t));				      \
> > -    (void) __mbsrtowcs_l (ws, &__s, l, &__st, loc);			      \
> > +    ws = malloc ((l + 1) * sizeof (wchar_t));				      \
> > +    if (ws != NULL)							      \
> > +      (void) __mbsrtowcs_l (ws, &__s, l, &__st, loc);			      \
> >    }
> >  #endif
> >  
> > @@ -1346,7 +1347,10 @@ __strftime_internal (CHAR_T *s, size_t maxsize, const CHAR_T *format,
> >  	    wchar_t *wczone;
> >  	    size_t len;
> >  	    widen (zone, wczone, len);
> > +	    if (wczone == NULL)
> > +	      return 0;
> >  	    cpy (len, wczone);
> > +	    free (wczone);
> >  	  }
> >  #else
> >  	  cpy (strlen (zone), zone);
> 
> Do we have a practical maximum size for the abbreviate timezone name?  The
> internal tz_rule 'name' field is just a pointer, but I think all timezones
> uses a maximum name size.
> 

I was able to pass a random string in via the TZ environment variable.
I'm not sure if that matters since the size of the buffer (s) and
maxsize would still limit the amount of bytes from the TZ variable.