Re: [PATCH] getaddrinfo: Get rid of alloca

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

On Fri, Jun 30, 2023 at 10:15:48AM -0300, Adhemerval Zanella Netto wrote:
> 
> 
> On 20/06/23 18:40, Joe Simmons-Talbott via Libc-alpha wrote:
> > Use a scratch_buffer rather than alloca to avoid potential stack
> > overflow.
> > ---
> >  sysdeps/posix/getaddrinfo.c | 22 ++++++++--------------
> >  1 file changed, 8 insertions(+), 14 deletions(-)
> > 
> > diff --git a/sysdeps/posix/getaddrinfo.c b/sysdeps/posix/getaddrinfo.c
> > index 0356b622be..442475d621 100644
> > --- a/sysdeps/posix/getaddrinfo.c
> > +++ b/sysdeps/posix/getaddrinfo.c
> > @@ -2404,22 +2404,17 @@ getaddrinfo (const char *name, const char *service,
> >        struct addrinfo *q;
> >        struct addrinfo *last = NULL;
> >        char *canonname = NULL;
> > -      bool malloc_results;
> >        size_t alloc_size = nresults * (sizeof (*results) + sizeof (size_t));
> > +      struct scratch_buffer buf;
> > +      scratch_buffer_init (&buf);
> >  
> > -      malloc_results
> > -	= !__libc_use_alloca (alloc_size);
> > -      if (malloc_results)
> > +      if (!scratch_buffer_set_array_size (&buf, 1, alloc_size))
> 
> I think it would be better to use:
> 
>   if (!scratch_buffer_set_array_size (&buf, nresults, 
> 				      sizeof (*results) + sizeof (size_t)))
>     [...]
> 
> To use the overflow checks done by scratch_buffer_set_array_size (
> sizeof (*results) + sizeof (size_t) is always safe so I think there is no
> need to add extra checks).

You are correct.  Thanks for catching that and for the review.  I've
pushed your suggestion as v2.

Thanks,
Joe