188 lines
5.5 KiB
Groff
188 lines
5.5 KiB
Groff
.\" Copyright (c) 1983, 1991, 1993
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.\" The Regents of the University of California. All rights reserved.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\" 4. Neither the name of the University nor the names of its contributors
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.\" may be used to endorse or promote products derived from this software
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.\" without specific prior written permission.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
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.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
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.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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.\" SUCH DAMAGE.
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.\"
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.\" @(#)setuid.2 8.1 (Berkeley) 6/4/93
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.\" $FreeBSD$
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.\"
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.Dd December 15, 2015
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.Dt SETUID 2
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.Os
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.Sh NAME
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.Nm setuid ,
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.Nm seteuid ,
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.Nm setgid ,
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.Nm setegid
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.Nd set user and group ID
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.Sh LIBRARY
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.Lb libc
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.Sh SYNOPSIS
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.In unistd.h
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.Ft int
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.Fn setuid "uid_t uid"
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.Ft int
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.Fn seteuid "uid_t euid"
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.Ft int
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.Fn setgid "gid_t gid"
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.Ft int
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.Fn setegid "gid_t egid"
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.Sh DESCRIPTION
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The
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.Fn setuid
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system call
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sets the real and effective
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user IDs and the saved set-user-ID of the current process
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to the specified value.
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.\" Comment out next block for !_POSIX_SAVED_IDS
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.\" The real user ID and the saved set-user-ID are changed only if the
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.\" effective user ID is that of the super user.
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.\" I.e.
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.\" .Fn setuid
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.\" system call is equal to
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.\" .Fn seteuid
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.\" system call if the effective user ID is not that of the super user.
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.\" End of block
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The
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.Fn setuid
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system call is permitted if the specified ID is equal to the real user ID
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.\" Comment out next line for !_POSIX_SAVED_IDS
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.\" or the saved set-user-ID
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.\" Next line is for Appendix B.4.2.2 case.
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or the effective user ID
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of the process, or if the effective user ID is that of the super user.
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.Pp
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The
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.Fn setgid
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system call
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sets the real and effective
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group IDs and the saved set-group-ID of the current process
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to the specified value.
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.\" Comment out next block for !_POSIX_SAVED_IDS
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.\" The real group ID and the saved set-group-ID are changed only if the
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.\" effective user ID is that of the super user.
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.\" I.e.
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.\" .Fn setgid
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.\" system call is equal to
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.\" .Fn setegid
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.\" system call if the effective user ID is not that of the super user.
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.\" End of block
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The
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.Fn setgid
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system call is permitted if the specified ID is equal to the real group ID
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.\" Comment out next line for !_POSIX_SAVED_IDS
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.\" or the saved set-group-ID
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.\" Next line is for Appendix B.4.2.2 case.
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or the effective group ID
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of the process, or if the effective user ID is that of the super user.
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.Pp
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The
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.Fn seteuid
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system call
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.Pq Fn setegid
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sets the effective user ID (group ID) of the
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current process.
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The effective user ID may be set to the value
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of the real user ID or the saved set-user-ID (see
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.Xr intro 2
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and
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.Xr execve 2 ) ;
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in this way, the effective user ID of a set-user-ID executable
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may be toggled by switching to the real user ID, then re-enabled
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by reverting to the set-user-ID value.
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Similarly, the effective group ID may be set to the value
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of the real group ID or the saved set-group-ID.
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.Sh RETURN VALUES
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.Rv -std
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.Sh ERRORS
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The system calls will fail if:
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.Bl -tag -width Er
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.It Bq Er EPERM
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The user is not the super user and the ID
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specified is not the real, effective ID, or saved ID.
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.El
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.Sh SEE ALSO
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.Xr getgid 2 ,
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.Xr getuid 2 ,
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.Xr issetugid 2 ,
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.Xr setregid 2 ,
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.Xr setreuid 2
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.Sh STANDARDS
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The
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.Fn setuid
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and
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.Fn setgid
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system calls are compliant with the
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.St -p1003.1-90
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specification with
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.Li _POSIX_SAVED_IDS
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.\" Uncomment next line for !_POSIX_SAVED_IDS
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not
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defined with the permitted extensions from Appendix B.4.2.2.
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The
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.Fn seteuid
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and
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.Fn setegid
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system calls are extensions based on the
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.Tn POSIX
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concept of
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.Li _POSIX_SAVED_IDS ,
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and have been proposed for a future revision of the standard.
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.Sh HISTORY
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The
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.Fn setuid
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and
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.Fn setgid
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functions appeared in
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.At v7 .
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.Sh SECURITY CONSIDERATIONS
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Read and write permissions to files are determined upon a call to
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.Xr open 2 .
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Once a file descriptor is open, dropping privilege does not affect
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the process's read/write permissions, even if the user ID specified
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has no read or write permissions to the file.
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These files normally remain open in any new process executed,
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resulting in a user being able to read or modify
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potentially sensitive data.
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.Pp
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To prevent these files from remaining open after an
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.Xr exec 3
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call, be sure to set the close-on-exec flag:
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.Bd -literal
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void
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pseudocode(void)
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{
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int fd;
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/* ... */
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fd = open("/path/to/sensitive/data", O_RDWR | O_CLOEXEC);
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if (fd == -1)
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err(1, "open");
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/* ... */
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execve(path, argv, environ);
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}
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.Ed
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