[PATCH libXdmcp] Use getrandom() syscall if available

[Alan Coopersmith]

On 04/ 3/17 12:17 PM, Mark Kettenis wrote:
>> From: Benjamin Tissoires <benjamin.tissoires at gmail.com>
>> Date: Mon, 3 Apr 2017 17:52:32 +0200
>>
>> On Mon, Apr 3, 2017 at 4:02 PM, Alan Coopersmith
>> <alan.coopersmith at oracle.com> wrote:
>>> 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.
>
> Doesn't Solaris have a proper arc4random_buf(3) in libc now though?

Yes - and if that was preferred over the raw syscall it would help,
but this patch looked like it always went to the syscall first, then
fell back to arc4random_buf.   (The similar patch for libICE appears
to be the other way around, which is better, only making the syscall
if HAVE_ARC4RANDOM_BUF isn't defined.)

Or did I misread it?

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