💾 Archived View for gmi.noulin.net › man › man2 › setregid32.2.gmi captured on 2024-08-31 at 13:41:11. Gemini links have been rewritten to link to archived content

View Raw

More Information

⬅️ Previous capture (2023-09-08)

-=-=-=-=-=-=-

SETREUID(2)                                                             Linux Programmer's Manual                                                            SETREUID(2)

NAME
       setreuid, setregid - set real and/or effective user or group ID

SYNOPSIS
       #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 <= 2.19: */ _BSD_SOURCE

DESCRIPTION
       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".

RETURN VALUE
       On success, zero is returned.  On error, -1 is returned, and errno is set to indicate the error.

       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  se‐
       treuid().

ERRORS
       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.

CONFORMING TO
       POSIX.1-2001, POSIX.1-2008, 4.3BSD (setreuid() and setregid() first appeared in 4.2BSD).

NOTES
       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).

SEE ALSO
       getgid(2), getuid(2), seteuid(2), setgid(2), setresuid(2), setuid(2), capabilities(7), credentials(7), user_namespaces(7)

Linux                                                                          2021-03-22                                                                    SETREUID(2)