[PATCH] getpw: Get rid of alloca

[Joe Simmons-Talbott]

Ping.

On Thu, Aug 10, 2023 at 09:45:47AM -0400, Joe Simmons-Talbott via Libc-alpha wrote:
> On Fri, Jul 07, 2023 at 04:04:00PM -0400, Joe Simmons-Talbott wrote:
> > Use a scratch_buffer rather than alloca to avoid potential stack
> > overflow.
> 
> Ping.
> 
> Thanks,
> Joe
> > ---
> >  pwd/getpw.c | 34 +++++++++++++++++++++++++++-------
> >  1 file changed, 27 insertions(+), 7 deletions(-)
> > 
> > diff --git a/pwd/getpw.c b/pwd/getpw.c
> > index cf747374b8..7a27d79910 100644
> > --- a/pwd/getpw.c
> > +++ b/pwd/getpw.c
> > @@ -15,8 +15,8 @@
> >     License along with the GNU C Library; if not, see
> >     <https://www.gnu.org/licenses/>.  */
> >  
> > -#include <alloca.h>
> >  #include <errno.h>
> > +#include <scratch_buffer.h>
> >  #include <stdio.h>
> >  #include <unistd.h>
> >  #include <pwd.h>
> > @@ -34,28 +34,48 @@ __getpw (__uid_t uid, char *buf)
> >    size_t buflen;
> >    char *tmpbuf;
> >    struct passwd resbuf, *p;
> > +  int retval = 0;
> > +  struct scratch_buffer sbuf;
> > +  scratch_buffer_init (&sbuf);
> >  
> >    if (buf == NULL)
> >      {
> >        __set_errno (EINVAL);
> > -      return -1;
> > +      retval =  -1;
> > +      goto error_out;
> >      }
> >  
> >    buflen = __sysconf (_SC_GETPW_R_SIZE_MAX);
> > -  tmpbuf = alloca (buflen);
> > +  if (!scratch_buffer_set_array_size (&sbuf, 1, buflen))
> > +    {
> > +      retval = -1;
> > +      goto error_out;
> > +    }
> > +  tmpbuf = sbuf.data;
> >  
> >    if (__getpwuid_r (uid, &resbuf, tmpbuf, buflen, &p) != 0)
> > -    return -1;
> > +    {
> > +      retval = -1;
> > +      goto error_out;
> > +    }
> >  
> >    if (p == NULL)
> > -    return -1;
> > +    {
> > +      retval = -1;
> > +      goto error_out;
> > +    }
> >  
> >    if (sprintf (buf, "%s:%s:%lu:%lu:%s:%s:%s", p->pw_name, p->pw_passwd,
> >  	       (unsigned long int) p->pw_uid, (unsigned long int) p->pw_gid,
> >  	       p->pw_gecos, p->pw_dir, p->pw_shell) < 0)
> > -    return -1;
> > +    {
> > +      retval = -1;
> > +      goto error_out;
> > +    }
> >  
> > -  return 0;
> > +error_out:
> > +  scratch_buffer_free (&sbuf);
> > +  return retval;
> >  }
> >  weak_alias (__getpw, getpw)
> >  
> > -- 
> > 2.39.2
> > 
>