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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 credentials 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 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.

     By default, a process does not command superuser powers if it has been
     imprisoned by the jail(2) system call.  There are cases however where
     this is appropriate, and this can be done by passing SUSER_ALLOWJAIL in
     the flag argument to the 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 chroot(2) implicit 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 superuser 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 indicates 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.