need privport patch for RHEL 7

[garlick]

The 9p transport privport patch was commited for kernel 3.11

Then Dominique Martinent recently fixed a bug

Need to backport these changes to the RHEL 7 kernel, e.g. 3.10.0-123.20.1.el7 in order to get this minimal security protection for 9nbd.

[garlick]

This patch applied to test centos kernel 3.10.0-229.el7.centos.x86_6

[garlick]

A test: diod.conf like this:

listen = { "0.0.0.0:564" }
auth_required = 0
exports = {
    { path="ctl" },
    { path="/tftpboot/images", opts="ro,privport" },
}

This works:

mount.diod -oprivport --9nbd-attach 127.0.0.1:/tftpboot/images/image /dev/9nbd0
mount -o ro /dev/9nbd0 /mnt

While this fails:

mount.diod  --9nbd-attach 127.0.0.1:/tftpboot/images/image /dev/9nbd0

The failure is not reported very well as noted in issue #1. The diod server reports

diod: attach(0@localhost:/tftpboot/images/image): access denied for export: Operation not permitted

but the mount.diod command hangs and the console says

[  540.872260] 9nbd0/ses17: 9P session restart due to protocol failure