Re: [PATCH] getsourcefilter: Get rid of alloca.

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

On Wed, May 31, 2023 at 09:27:30AM -0300, Adhemerval Zanella Netto wrote:
> 
> 
> On 30/05/23 15:13, Joe Simmons-Talbott via Libc-alpha wrote:
> > Use a scratch_buffer rather than alloca to avoid potential stack
> > overflows.
> 
> LGTM, thanks.
> 
> Reviewed-by: Adhemerval Zanella  <adhemerval.zanella@linaro.org>

Thanks for the review.  Would you mind committing this please?

Thanks,
Joe
> 
> > ---
> >  sysdeps/unix/sysv/linux/getsourcefilter.c | 24 +++++++----------------
> >  1 file changed, 7 insertions(+), 17 deletions(-)
> > 
> > diff --git a/sysdeps/unix/sysv/linux/getsourcefilter.c b/sysdeps/unix/sysv/linux/getsourcefilter.c
> > index b9ba58c23a..461ad889a9 100644
> > --- a/sysdeps/unix/sysv/linux/getsourcefilter.c
> > +++ b/sysdeps/unix/sysv/linux/getsourcefilter.c
> > @@ -16,10 +16,10 @@
> >     License along with the GNU C Library; if not, see
> >     <https://www.gnu.org/licenses/>.  */
> >  
> > -#include <alloca.h>
> >  #include <assert.h>
> >  #include <errno.h>
> >  #include <stdlib.h>
> > +#include <scratch_buffer.h>
> >  #include <string.h>
> >  #include <stdint.h>
> >  #include <netatalk/at.h>
> > @@ -95,17 +95,12 @@ getsourcefilter (int s, uint32_t interface, const struct sockaddr *group,
> >    /* We have to create an struct ip_msfilter object which we can pass
> >       to the kernel.  */
> >    socklen_t needed = GROUP_FILTER_SIZE (*numsrc);
> > -  int use_alloca = __libc_use_alloca (needed);
> >  
> > -  struct group_filter *gf;
> > -  if (use_alloca)
> > -    gf = (struct group_filter *) alloca (needed);
> > -  else
> > -    {
> > -      gf = (struct group_filter *) malloc (needed);
> > -      if (gf == NULL)
> > -	return -1;
> > -    }
> > +  struct scratch_buffer buf;
> > +  scratch_buffer_init (&buf);
> > +  if (!scratch_buffer_set_array_size (&buf, 1, needed))
> > +    return -1;
> > +  struct group_filter *gf = buf.data;
> >  
> >    gf->gf_interface = interface;
> >    memcpy (&gf->gf_group, group, grouplen);
> > @@ -135,12 +130,7 @@ getsourcefilter (int s, uint32_t interface, const struct sockaddr *group,
> >  	}
> >      }
> >  
> > -  if (! use_alloca)
> > -    {
> > -      int save_errno = errno;
> > -      free (gf);
> > -      __set_errno (save_errno);
> > -    }
> > +  scratch_buffer_free (&buf);
> >  
> >    return result;
> >  }
>