[PATCH v2] check_native: Get rid of alloca

[Joe Simmons-Talbott]

On Mon, Jun 12, 2023 at 06:09:58PM -0300, Adhemerval Zanella Netto wrote:
> 
> 
> On 01/06/23 11:55, Joe Simmons-Talbott via Libc-alpha wrote:
> > Use malloc rather than alloca to avoid potential stack overflow.
> 
> LGTM with the small nit below fixed.

Thanks for the review.  Fixed in v3.

Thanks,
Joe
> 
> Reviewed-by: Adhemerval Zanella  <adhemerval.zanella@linaro.org>
> 
> > ---
> > Changes to v1:
> >   * Do not use a cleanup handler.
> > 
> >  sysdeps/unix/sysv/linux/check_native.c | 35 ++++++++------------------
> >  1 file changed, 11 insertions(+), 24 deletions(-)
> > 
> > diff --git a/sysdeps/unix/sysv/linux/check_native.c b/sysdeps/unix/sysv/linux/check_native.c
> > index 34876ca624..601f14e5b0 100644
> > --- a/sysdeps/unix/sysv/linux/check_native.c
> > +++ b/sysdeps/unix/sysv/linux/check_native.c
> > @@ -48,11 +48,20 @@ __check_native (uint32_t a1_index, int *a1_native,
> >    nladdr.nl_family = AF_NETLINK;
> >  
> >    socklen_t addr_len = sizeof (nladdr);
> > -  bool use_malloc = false;
> >  
> >    if (fd < 0)
> >      return;
> >  
> > +  /* Netlink requires that user buffer needs to be either 8kb or page size
> > +     (whichever is bigger), however this has been changed over time and now
> > +     8Kb is sufficient (check NLMSG_DEFAULT_SIZE on Linux
> > +     linux/include/linux/netlink.h).  */
> > +  const size_t buf_size = 8192;
> > +  char *buf = malloc (buf_size);
> > +
> > +  if (buf == NULL)
> > +    goto out;
> > +
> >    if (__bind (fd, (struct sockaddr *) &nladdr, sizeof (nladdr)) != 0
> >        || __getsockname (fd, (struct sockaddr *) &nladdr, &addr_len) != 0)
> >      goto out;
> > @@ -81,26 +90,6 @@ __check_native (uint32_t a1_index, int *a1_native,
> >    memset (&nladdr, '\0', sizeof (nladdr));
> >    nladdr.nl_family = AF_NETLINK;
> >  
> > -#ifdef PAGE_SIZE
> > -  /* Help the compiler optimize out the malloc call if PAGE_SIZE
> > -     is constant and smaller or equal to PTHREAD_STACK_MIN/4.  */
> > -  const size_t buf_size = PAGE_SIZE;
> > -#else
> > -  const size_t buf_size = __getpagesize ();
> > -#endif
> > -  char *buf;
> > -
> > -  if (__libc_use_alloca (buf_size))
> > -    buf = alloca (buf_size);
> > -  else
> > -    {
> > -      buf = malloc (buf_size);
> > -      if (buf != NULL)
> > -	use_malloc = true;
> > -      else
> > -	goto out;
> > -    }
> > -
> >    struct iovec iov = { buf, buf_size };
> >  
> >    if (TEMP_FAILURE_RETRY (__sendto (fd, (void *) &req, sizeof (req), 0,
> > @@ -170,7 +159,5 @@ __check_native (uint32_t a1_index, int *a1_native,
> >  
> >  out:
> >    __close_nocancel_nostatus (fd);
> > -
> > -  if (use_malloc)
> > -    free (buf);
> > +  free(buf);
> 
> Space before '('.
> 
> >  }
>