SETREGID(3P) POSIX Programmer's Manual SETREGID(3P)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.
NAMEsetregid — 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 fea‐
ture. 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>
COPYRIGHT
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 Electri‐
cal 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.ker‐
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IEEE/The Open Group 2013 SETREGID(3P)
