bionic (3) setregid.3posix.gz

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PROLOG
       This  manual  page  is part of the POSIX Programmer's Manual.  The Linux implementation of this interface
       may differ (consult the corresponding Linux manual page for details of Linux behavior), or the  interface
       may not be implemented on Linux.


NAME
       setregid — set real and effective group IDs


SYNOPSIS
       #include <unistd.h>

       int setregid(gid_t rgid, gid_t egid);


DESCRIPTION
       The setregid() function shall set the real and effective group IDs of the calling process.

       If rgid is −1, the real group ID shall not be changed; if egid is −1, the effective group ID shall not be
       changed.

       The real and effective group IDs may be set to different values in the same call.

       Only a process with appropriate privileges can set the real group ID and the effective group  ID  to  any
       valid value.

       A  non-privileged process can set either the real group ID to the saved set-group-ID from one of the exec
       family of functions, or the effective group ID to the saved set-group-ID or the real group ID.

       If the real group ID is being set (rgid is not −1), or the effective group ID is being set to a value not
       equal  to the real group ID, then the saved set-group-ID of the current process shall be set equal to the
       new effective group ID.

       Any supplementary group IDs of the calling process remain unchanged.


RETURN VALUE
       Upon successful completion, 0 shall be returned. Otherwise,  −1  shall  be  returned  and  errno  set  to
       indicate the error, and neither of the group IDs are changed.


ERRORS
       The setregid() function shall fail if:

       EINVAL The value of the rgid or egid argument is invalid or out-of-range.

       EPERM  The  process  does not have appropriate privileges and a change other than changing the real group
              ID to the saved set-group-ID, or changing the effective group ID to the real group ID or the saved
              set-group-ID, was requested.

       The following sections are informative.


EXAMPLES
       None.


APPLICATION USAGE
       If  a  non-privileged  set-group-ID process sets its effective group ID to its real group ID, it can only
       set its effective group ID back to the previous value if rgid was −1 in the setregid()  call,  since  the
       saved-group-ID  is  not  changed  in  that case. If rgid was equal to the real group ID in the setregid()
       call, then the saved set-group-ID will also have been changed to the real user ID.


RATIONALE
       Earlier versions of this standard did  not  specify  whether  the  saved  set-group-ID  was  affected  by
       setregid()  calls. This version specifies common existing practice that constitutes an important security
       feature. The ability to set both the effective group ID and saved set-group-ID to be the same as the real
       group  ID  means  that  any  security weakness in code that is executed after that point cannot result in
       malicious code being executed with the previous effective group ID. Privileged applications could already
       do this using just setgid(), but for non-privileged applications the only standard method available is to
       use this feature of setregid().


FUTURE DIRECTIONS
       None.


SEE ALSO
       exec, getegid(), geteuid(), getgid(), getuid(), setegid(), seteuid(), setgid(), setreuid(), setuid()

       The Base Definitions volume of POSIX.1‐2008, <unistd.h>


       Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2013 Edition,
       Standard  for  Information Technology -- Portable Operating System Interface (POSIX), The Open Group Base
       Specifications Issue 7, Copyright (C) 2013 by the Institute of Electrical and Electronics Engineers,  Inc
       and  The  Open Group.  (This is POSIX.1-2008 with the 2013 Technical Corrigendum 1 applied.) In the event
       of any discrepancy between this version and the original IEEE and The Open Group Standard,  the  original
       IEEE and The Open Group Standard is the referee document. The original Standard can be obtained online at
       http://www.unix.org/online.html .

       Any typographical or formatting errors that appear in this page are most likely to have  been  introduced
       during   the   conversion  of  the  source  files  to  man  page  format.  To  report  such  errors,  see
       https://www.kernel.org/doc/man-pages/reporting_bugs.html .