CVE request - kernel: xfs infoleak

[Eugene Teo <eugene () redhat com>]

From Dan R0s3nbug5, "The FSGEOMETRY_V1 ioctl (and its compat 
equivalent) calls out to xfs_fs_geometry() with a version number of 3. 
This code path does not fill in the logsunit member of the passed 
xfs_fsop_geom_t, leading to the leaking of four bytes of uninitialized 
stack data to potentially unprivileged callers.  Since all other members 
are filled in all code paths and there are no padding bytes in this 
structure, it's safe to avoid an expensive memset() in favor of just 
clearing this one field."

https://patchwork.kernel.org/patch/555461/
https://bugzilla.redhat.com/show_bug.cgi?id=677260

Eugene