.\"
.\" Copyright (c) 1996 Julian R Elischer
.\" All rights reserved.
.\"
.\" This code is derived from software contributed by Kenneth Stailey.
.\"
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.\" modification, are permitted provided that the following conditions
.\" are met:
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.\"    documentation and/or other materials provided with the distribution.
.\" 3. All advertising materials mentioning features or use of this software
.\"    must display the following acknowledgement:
.\"	This product includes software developed for the FreeBSD Project
.\"	by Julian R Elischer
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.\"    derived from this software without specific prior written permission.
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.\" $FreeBSD$
.\"
.Dd April 2, 2002
.Dt SUSER 9
.Os
.Sh NAME
.Nm suser ,
.Nm suser_cred
.Nd check if credentials have superuser privilege
.Sh SYNOPSIS
.In sys/param.h
.In sys/systm.h
.Ft int
.Fn suser "struct thread *td"
.Ft int
.Fn suser_cred "struct ucred *cred" "int flag"
.Sh DESCRIPTION
The
.Fn suser
and
.Fn suser_cred
functions check if the credentials given include superuser powers.
.Pp
The
.Fn suser
function is the most common, and should be used unless special
circumstances dictate otherwise.
.Pp
The
.Fn suser_cred
function should be used when the credentials to be checked are
not the thread's own, when there is no thread, when superuser
powers should be extended to imprisoned roots, or when the credential
to be checked is the real user rather than the effective user.
.Pp
By default, a process does not command superuser powers if it has
been imprisoned by the
.Xr jail 2
system call.
There are cases however where this is appropriate, and this can
be done by passing
.Dv SUSER_ALLOWJAIL
in the
.Fa flag
argument to the
.Fn suser_cred
function.
It is important to review carefully in each case that
this does not weaken the prison.
Generally, only where the action is protected by
.Xr chroot 2
implicit in the
.Xr jail 2
call should such powers be granted.
.Pp
By default, the credential checked is the effective user.  There are cases 
where it is instead necessary to check the real user (for example, when 
determining if resource limits should be applied), and this can be done
by passing the
.Dv SUSER_RUID
flag in the
.Fa flag
argument to the
.Fn suser_cred
function.
.Pp
The
.Fn suser
and
.Fn suser_cred
functions note the fact that superuser powers have been used in the
process structure of the process specified.
Because part of their function is to notice
whether superuser powers have been used,
the functions should only be called after other permission
possibilities have been exhausted.
.Sh RETURN VALUES
The
.Fn suser
and
.Fn suser_cred
functions return 0 if the user has superuser powers and
.Er EPERM
otherwise.
This is the
.Em reverse logic
of some other implementations of
.Fn suser
in which a TRUE response indicates superuser powers.
.Sh SEE ALSO
.Xr chroot 2 ,
.Xr jail 2
.Sh BUGS
The
.Fn suser
and
.Fn suser_cred
functions don't, in fact, record that superuser privileges have been
used, and haven't done so since August 2000.