Attempting to acquire the value of the 'kern.hostname' ctl from a kext by calling sysctlbyname() returns EPERM with no hostname returned. sysctlbyname() is aliased to kernel_sysctlbyname():
config/Libkern.exports:839:_sysctlbyname:_kernel_sysctlbyname
Looking at the implementation of kernel_sysctlbyname(), EPERM is returned by sysctl_root(). Not sure how to correctly identify the point of failure.
Alternately, calling
sysctlbyname("hw.ncpu")
does return the value set for the ctl.
The kext was compiled with SYSCTL_DEF_ENABLED defined to have the relevant section of sys/sysctl.h enabled.
bsd_hostname() is a private symbol which is inaccessible to my kext.
% sysctl -n kern.hostname
does return the host name, so the ctl must be set.
Is it possible to get the name of a host from the context of my kext?
Thanks.
Looking at the implementation of kernel_sysctlbyname(), EPERM is returned by sysctl_root(). Not sure how to correctly identify the point of failure.
I believe your EPERM failure is coming from this check in sysctl_root:
/*
* If we're inside the kernel, the OID must be marked as kernel-valid.
*/
if (from_kernel && !(oid->oid_kind & CTLFLAG_KERN))
{
error = (EPERM);
goto err;
}
sysctl_hostname is defined here and is not marked with CTLFLAG_KERN, and is thus not available in the kernel:
SYSCTL_PROC(_kern, KERN_HOSTNAME, hostname,
CTLTYPE_STRING | CTLFLAG_RW | CTLFLAG_LOCKED,
0, 0, sysctl_hostname, "A", "");
Note: On some of our platforms, the full implementation of sysctl_hostname includes additional checks entitlement checks that are not included in the code above. On those platforms, kern.hostname won't work in user space unless the process has the "com.apple.developer.device-information.user-assigned-device-name" entitlement.
bsd_hostname() is a private symbol which is inaccessible to my kext.
FYI, as far as I can tell, "bsd_hostname" is effectively "dead" code. It doesn't appear to be used by XNU or any current KEXT.
__
Kevin Elliott
DTS Engineer, CoreOS/Hardware
