Re: [PATCH] time: strftime_l: Avoid an unbounded alloca.

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

On Tue, May 23, 2023 at 04:11:05PM -0300, Adhemerval Zanella Netto wrote:
> 
> 
> On 22/05/23 15:32, Joe Simmons-Talbott via Libc-alpha wrote:
> > Avoid possible stack overflow by removing alloca() and converting to
> > wide characters within the buffer.
> > 
> > Suggested-by: Paul Eggert <eggert@cs.ucla.edu>
> > ---
> > Supersedes: https://sourceware.org/pipermail/libc-alpha/2023-May/147996.html
> >  time/strftime_l.c | 39 +++++++++++++++++++++++++--------------
> >  1 file changed, 25 insertions(+), 14 deletions(-)
> > 
> > diff --git a/time/strftime_l.c b/time/strftime_l.c
> > index 402c6c4111..bb8e9e7f25 100644
> > --- a/time/strftime_l.c
> > +++ b/time/strftime_l.c
> > @@ -267,15 +267,6 @@ static const CHAR_T zeroes[16] = /* "0000000000000000" */
> >  #  undef __mbsrtowcs_l
> >  #  define __mbsrtowcs_l(d, s, l, st, loc) __mbsrtowcs (d, s, l, st)
> >  # endif
> > -# define widen(os, ws, l) \
> > -  {									      \
> > -    mbstate_t __st;							      \
> > -    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);			      \
> > -  }
> >  #endif
> >  
> >  
> > @@ -1342,11 +1333,31 @@ __strftime_internal (CHAR_T *s, size_t maxsize, const CHAR_T *format,
> >  #ifdef COMPILE_WIDE
> >  	  {
> >  	    /* The zone string is always given in multibyte form.  We have
> > -	       to transform it first.  */
> > -	    wchar_t *wczone;
> > -	    size_t len;
> > -	    widen (zone, wczone, len);
> > -	    cpy (len, wczone);
> > +               to convert it to wide character.  */
> > +            size_t w = pad == L_('-') || width < 0 ? 0 : width;
> > +            char const *z = zone;
> > +            mbstate_t st = {0};
> > +            size_t len = __mbsrtowcs_l (p, &z, maxsize - i, &st, loc);
> > +            if (len == (size_t) -1)
> > +              return 0;
> > +            size_t incr = len < w ? w : len;
> > +            if (incr >= maxsize - i)
> > +              {
> > +                errno = ERANGE;
> > +                return 0;
> > +              }
> > +            if (p)
> > +              {
> > +                if (len < w)
> > +                  {
> > +                    size_t delta = w - len;
> > +                    wmemmove (p + delta, p, len);
> 
> 
> This triggers a local PLT failure:
> 
> $ cat elf/check-localplt.out
> Extra PLT reference: libc.so: wmemmove

Thanks for catching that.  Should be fixed in v2.

Thanks,
Joe