.\"
.\" 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
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.\" $FreeBSD$
.\"
.Dd August 30, 2007
.Dt SUSER 9
.Os
.Sh NAME
.Nm suser ,
.Nm suser_cred
.Nd check if credentials have superuser privileges
.Sh SYNOPSIS
.In sys/priv.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
These interfaces have now been obsoleted by
.Xr priv 9 ,
and are provided only for compatibility with third party kernel modules that
have not yet been updated to the new interface.
They should not be used in any new kernel code.
.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
Whether or not a privilege is permitted in a
.Xr jail 8
depends on logic in
.Fn prison_priv_check .
.Pp
In general, privileges are assigned based on the effective user ID; in some
cases, the real user ID may be used.
.Pp
The
.Fa flags
field is currently unused.
.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 ,
.Xr priv 9
.Sh BUGS
The
.Fn suser
and
.Fn suser_cred
functions do not, in fact, record that superuser privileges have been
used, and have not done so since August 2000.