Ubuntu manuals

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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 spe‐
      cial 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.  Gen‐
      erally, 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 pow‐
      ers 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.
      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.
      chroot(2), jail(2)
 

BUGS

      The suser() and suser_cred() functions do not, in fact, record that supe‐
      ruser privileges have been used, and have not done so since August 2000.