[PATCH] grantpt: Get rid of alloca

[Florian Weimer]

* Joe Simmons-Talbott via Libc-alpha:

> Replace alloca with a scratch_buffer to avoid potential stack overflows.
> ---
>  sysdeps/unix/grantpt.c | 12 +++++++++++-
>  1 file changed, 11 insertions(+), 1 deletion(-)
>
> diff --git a/sysdeps/unix/grantpt.c b/sysdeps/unix/grantpt.c
> index 38fce52576..e5d2390bf2 100644
> --- a/sysdeps/unix/grantpt.c
> +++ b/sysdeps/unix/grantpt.c
> @@ -20,6 +20,7 @@
>  #include <fcntl.h>
>  #include <grp.h>
>  #include <limits.h>
> +#include <scratch_buffer.h>
>  #include <stdlib.h>
>  #include <string.h>
>  #include <sys/resource.h>
> @@ -147,7 +148,14 @@ grantpt (int fd)
>  	/* `sysconf' does not support _SC_GETGR_R_SIZE_MAX.
>  	   Try a moderate value.  */
>  	grbuflen = 1024;
> -      grtmpbuf = (char *) __alloca (grbuflen);
> +      struct scratch_buffer sbuf;
> +      scratch_buffer_init (&sbuf);
> +      if (!scratch_buffer_set_array_size (&sbuf, 1, grbuflen))
> +	{
> +	  retval -1;
> +	  goto cleanup;
> +	}
> +      grtmpbuf = sbuf.data;
>        __getgrnam_r (TTY_GROUP, &grbuf, grtmpbuf, grbuflen, &p);
>        if (p != NULL)
>  	tty_gid = p->gr_gid;
> @@ -255,6 +263,8 @@ grantpt (int fd)
>    if (buf != _buf)
>      free (buf);
>  
> +  scratch_buffer_free(sbuf);
> +
>    return retval;
>  }
>  libc_hidden_def (grantpt)

How did you test this?  This code is only used on Hurd due to the
override in sysdeps/unix/sysv/linux/grantpt.c.

Maybe the hurd maintainers could review this change?

Thanks,
Florian