[PATCH libXdmcp] Use getrandom() syscall if available

[walter harms]

Am 03.04.2017 14:52, schrieb Benjamin Tissoires:
> This allows to fix CVE-2017-2625 on Linux platforms without pulling in
> libbsd.
> The syscall getrandom is available since kernel v3.17. The code first
> tries to use the syscall on a supported kernel. If the syscall fails,
> it falls back to the current (vulnerable) code.
> We do not implement the glibc getrandom() call given that it's only
> available in glibc 2.25, and the #if dance is already messy here.
> 
> Signed-off-by: Benjamin Tissoires <benjamin.tissoires at gmail.com>
> ---
>  Key.c        | 12 ++++++++++++
>  configure.ac |  3 +++
>  2 files changed, 15 insertions(+)
> 
> diff --git a/Key.c b/Key.c
> index a09b316..61b07db 100644
> --- a/Key.c
> +++ b/Key.c
> @@ -36,6 +36,10 @@ in this Software without prior written authorization from The Open Group.
>  #include <bsd/stdlib.h> /* for arc4random_buf() */
>  #endif
>  
> +#if HAVE_DECL_SYS_GETRANDOM
> +#include <sys/syscall.h> /* for SYS_getrandom */
> +#endif
> +
>  #ifndef HAVE_ARC4RANDOM_BUF
>  static void
>  getbits (long data, unsigned char *dst)
> @@ -68,6 +72,14 @@ XdmcpGenerateKey (XdmAuthKeyPtr key)
>  #ifndef HAVE_ARC4RANDOM_BUF
>      long    lowbits, highbits;
>  
> +#if HAVE_DECL_SYS_GETRANDOM
> +    int ret;
> +
> +    ret = syscall(SYS_getrandom, key->data, 8, 0);
> +    if (ret == 8)
> +	return;
> +#endif
> +

i am not an expert on syscalls but would it help to test for
SYS_getrandom directly ?

re,
 wh


>      srandom ((int)getpid() ^ time((Time_t *)0));
>      lowbits = random ();
>      highbits = random ();
> diff --git a/configure.ac b/configure.ac
> index 2288502..d0d4d05 100644
> --- a/configure.ac
> +++ b/configure.ac
> @@ -63,6 +63,9 @@ case $host_os in
>          ;;
>  esac
>  
> +# Checks for syscalls
> +AC_CHECK_DECLS([SYS_getrandom], [], [], [[#include <sys/syscall.h>]])
> +
>  # Checks for library functions.
>  AC_CHECK_LIB([bsd], [arc4random_buf])
>  AC_CHECK_FUNCS([srand48 lrand48 arc4random_buf])