Re: [PATCH] fxprintf: Get rid of alloca

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

On Wed, Jul 19, 2023 at 03:12:43PM -0300, Adhemerval Zanella Netto wrote:
> 
> 
> On 07/07/23 14:53, Joe Simmons-Talbott via Libc-alpha wrote:
> > Use a scratch_buffer rather than alloca/malloc to avoid potential stack
> > overflow.
> 
> LGTM, thanks.
> 
> Reviewed-by: Adhemerval Zanella  <adhemerval.zanella@linaro.org>

Should I apply this despite the seemingly unrelated test timeout[1] in
CI?

[1]
https://patchwork.sourceware.org/project/glibc/patch/20230707175349.2096131-1-josimmon@redhat.com/

Thanks,
Joe
> 
> > ---
> >  stdio-common/fxprintf.c | 14 ++++++--------
> >  1 file changed, 6 insertions(+), 8 deletions(-)
> > 
> > diff --git a/stdio-common/fxprintf.c b/stdio-common/fxprintf.c
> > index f0ac9654ab..88501ab61f 100644
> > --- a/stdio-common/fxprintf.c
> > +++ b/stdio-common/fxprintf.c
> > @@ -15,6 +15,7 @@
> >     License along with the GNU C Library; if not, see
> >     <https://www.gnu.org/licenses/>.  */
> >  
> > +#include <scratch_buffer.h>
> >  #include <stdarg.h>
> >  #include <stdio.h>
> >  #include <stdlib.h>
> > @@ -34,20 +35,18 @@ locked_vfxprintf (FILE *fp, const char *fmt, va_list ap,
> >    wchar_t *wfmt;
> >    mbstate_t mbstate;
> >    int res;
> > -  int used_malloc = 0;
> >    size_t len = strlen (fmt) + 1;
> > +  struct scratch_buffer buf;
> > +  scratch_buffer_init (&buf);
> >  
> >    if (__glibc_unlikely (len > SIZE_MAX / sizeof (wchar_t)))
> >      {
> >        __set_errno (EOVERFLOW);
> >        return -1;
> >      }
> 
> This check is redundant, but scratch_buffer_set_array_size would return
> ENOMEM in this case.  I guess it should not change this for now.
> 
> > -  if (__libc_use_alloca (len * sizeof (wchar_t)))
> > -    wfmt = alloca (len * sizeof (wchar_t));
> > -  else if ((wfmt = malloc (len * sizeof (wchar_t))) == NULL)
> > +  if (!scratch_buffer_set_array_size (&buf, sizeof (wchar_t), len))
> >      return -1;
> > -  else
> > -    used_malloc = 1;
> > +  wfmt = buf.data;
> >  
> >    memset (&mbstate, 0, sizeof mbstate);
> >    res = __mbsrtowcs (wfmt, &fmt, len, &mbstate);
> > @@ -55,8 +54,7 @@ locked_vfxprintf (FILE *fp, const char *fmt, va_list ap,
> >    if (res != -1)
> >      res = __vfwprintf_internal (fp, wfmt, ap, mode_flags);
> >  
> > -  if (used_malloc)
> > -    free (wfmt);
> > +  scratch_buffer_free (&buf);
> >  
> >    return res;
> >  }
>