suser(9)

NAME

suser, suser_cred - check if credentials have superuser

privilege

SYNOPSIS

#include <sys/param.h>
#include <sys/systm.h>
int
suser(struct thread *td);
int
suser_cred(struct ucred *cred, int flag);

DESCRIPTION

The suser() and suser_cred() functions check if the creden

tials given
include superuser powers.

The suser() function is the most common, and should be used

unless special circumstances dictate otherwise.

The suser_cred() function should be used when the creden

tials 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.

By default, a process does not command superuser powers if

it has been
imprisoned by the jail(2) system call. There are cases how

ever where
this is appropriate, and this can be done by passing SUS

ER_ALLOWJAIL in
the flag argument to the suser_cred() function. It is im

portant to
review carefully in each case that this does not weaken the

prison. Generally, only where the action is protected by chroot(2) im

plicit in the
jail(2) call should such powers be granted.

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 SUSER_RUID flag in the flag argument to

the
suser_cred() function.

The suser() and 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 superus

er powers have
been used, the functions should only be called after other

permission
possibilities have been exhausted.

RETURN VALUES

The suser() and suser_cred() functions return 0 if the user

has superuser
powers and EPERM otherwise. This is the reverse logic of

some other
implementations of suser() in which a TRUE response indi

cates superuser
powers.

SEE ALSO

chroot(2), jail(2)

BUGS

The suser() and suser_cred() functions do not, in fact,

record that superuser privileges have been used, and have not done so since

August 2000.

BSD April 2, 2002

BSD