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NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | CONFORMING TO | NOTES | SEE ALSO | COLOPHON |
SETREUID(2) Linux Programmer's Manual SETREUID(2)
setreuid, setregid - set real and/or effective user or group ID
#include <sys/types.h>
#include <unistd.h>
int setreuid(uid_t ruid, uid_t euid);
int setregid(gid_t rgid, gid_t egid);
Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
setreuid(), setregid():
_XOPEN_SOURCE >= 500
|| /* Since glibc 2.19: */ _DEFAULT_SOURCE
|| /* Glibc versions <= 2.19: */ _BSD_SOURCE
setreuid() sets real and effective user IDs of the calling process.
Supplying a value of -1 for either the real or effective user ID
forces the system to leave that ID unchanged.
Unprivileged processes may only set the effective user ID to the real
user ID, the effective user ID, or the saved set-user-ID.
Unprivileged users may only set the real user ID to the real user ID
or the effective user ID.
If the real user ID is set (i.e., ruid is not -1) or the effective
user ID is set to a value not equal to the previous real user ID, the
saved set-user-ID will be set to the new effective user ID.
Completely analogously, setregid() sets real and effective group ID's
of the calling process, and all of the above holds with "group"
instead of "user".
On success, zero is returned. On error, -1 is returned, and errno is
set appropriately.
Note: there are cases where setreuid() can fail even when the caller
is UID 0; it is a grave security error to omit checking for a failure
return from setreuid().
EAGAIN The call would change the caller's real UID (i.e., ruid does
not match the caller's real UID), but there was a temporary
failure allocating the necessary kernel data structures.
EAGAIN ruid does not match the caller's real UID and this call would
bring the number of processes belonging to the real user ID
ruid over the caller's RLIMIT_NPROC resource limit. Since
Linux 3.1, this error case no longer occurs (but robust
applications should check for this error); see the description
of EAGAIN in execve(2).
EINVAL One or more of the target user or group IDs is not valid in
this user namespace.
EPERM The calling process is not privileged (on Linux, does not have
the necessary capability in its user namespace: CAP_SETUID in
the case of setreuid(), or CAP_SETGID in the case of
setregid()) and a change other than (i) swapping the effective
user (group) ID with the real user (group) ID, or (ii) setting
one to the value of the other or (iii) setting the effective
user (group) ID to the value of the saved set-user-ID (saved
set-group-ID) was specified.
POSIX.1-2001, POSIX.1-2008, 4.3BSD (setreuid() and setregid() first
appeared in 4.2BSD).
Setting the effective user (group) ID to the saved set-user-ID (saved
set-group-ID) is possible since Linux 1.1.37 (1.1.38).
POSIX.1 does not specify all of the UID changes that Linux permits
for an unprivileged process. For setreuid(), the effective user ID
can be made the same as the real user ID or the saved set-user-ID,
and it is unspecified whether unprivileged processes may set the real
user ID to the real user ID, the effective user ID, or the saved set-
user-ID. For setregid(), the real group ID can be changed to the
value of the saved set-group-ID, and the effective group ID can be
changed to the value of the real group ID or the saved set-group-ID.
The precise details of what ID changes are permitted vary across
implementations.
POSIX.1 makes no specification about the effect of these calls on the
saved set-user-ID and saved set-group-ID.
The original Linux setreuid() and setregid() system calls supported
only 16-bit user and group IDs. Subsequently, Linux 2.4 added
setreuid32() and setregid32(), supporting 32-bit IDs. The glibc
setreuid() and setregid() wrapper functions transparently deal with
the variations across kernel versions.
C library/kernel differences
At the kernel level, user IDs and group IDs are a per-thread
attribute. However, POSIX requires that all threads in a process
share the same credentials. The NPTL threading implementation
handles the POSIX requirements by providing wrapper functions for the
various system calls that change process UIDs and GIDs. These
wrapper functions (including those for setreuid() and setregid())
employ a signal-based technique to ensure that when one thread
changes credentials, all of the other threads in the process also
change their credentials. For details, see nptl(7).
getgid(2), getuid(2), seteuid(2), setgid(2), setresuid(2), setuid(2),
capabilities(7), credentials(7), user_namespaces(7)
This page is part of release 4.12 of the Linux man-pages project. A
description of the project, information about reporting bugs, and the
latest version of this page, can be found at
https://www.kernel.org/doc/man-pages/.
Linux 2016-10-08 SETREUID(2)
Pages that refer to this page: execve(2), getgid(2), getresuid(2), getuid(2), seteuid(2), setgid(2), setresuid(2), setuid(2), syscalls(2), capabilities(7), credentials(7), nptl(7), user_namespaces(7)