[PATCH libXdmcp] Use getrandom() syscall if available

[Alan Coopersmith]

On 04/ 3/17 05:52 AM, Benjamin Tissoires wrote:
> 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>

This is dangerous - Solaris <sys/syscall.h> defines SYS_getrandom, but
I don't know if our syscall arguments/semantics are the same, and we
only support applications calling the libc getrandom() function, not the
raw syscall.

> 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])
>

Could you move that check up into the case $host_os section above it
under a new case for *linux* perhaps?

-- 
	-Alan Coopersmith-              alan.coopersmith at oracle.com
	 Oracle Solaris Engineering - http://blogs.oracle.com/alanc