Re: CVE-2014-9900 fix is not upstream

On Tue, Aug 23, 2016 at 01:34:05PM -0700, Joe Perches wrote:

On Tue, 2016-08-23 at 21:09 +0100, Al Viro wrote:

quoted

On Tue, Aug 23, 2016 at 11:24:06AM -0700, David Miller wrote:
... and then we can file a bug report against the sodding compiler.  Note
that
struct ethtool_wolinfo {
        __u32   cmd;
        __u32   supported;
        __u32   wolopts;
        __u8    sopass[SOPASS_MAX];	// 6, actually
};
is not going to *have* padding.  Not on anything even remotely sane.
If array of 6 char as member of a struct requires 64bit alignment on some
architecture, I would really like some of what the designers of that ABI
must have been smoking.

try this on x86-64

$ pahole -C ethtool_wolinfo vmlinux
struct ethtool_wolinfo {
	__u32                      cmd;                  /*     0     4 */
	__u32                      supported;            /*     4     4 */
	__u32                      wolopts;              /*     8     4 */
	__u8                       sopass[6];            /*    12     6 */

	/* size: 20, cachelines: 1, members: 4 */
	/* padding: 2 */
	/* last cacheline: 20 bytes */
};

That would be padding after the structure elements.

I think what was meant is that it won't add padding in the middle of the
structure due to alignment, ie it isn't doing:

struct ethtool_wolinfo {
	__u32                      cmd;                  /*     0     4 */
	__u32                      supported;            /*     4     4 */
	__u32                      wolopts;              /*     8     4 */
	<4 bytes padding here>
	__u8                       sopass[6];            /*    16     6 */
};

which would have 4 bytes of padding in the middle between wolopts
and sopass.

I would not think it is the compilers job to worry about what is after
your structure elements, since you shouldn't be going there.

-- 
Len Sorensen