freebsd-src/lib/libsys/setgroups.2

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.Dd January 19, 2018
.Dt SETGROUPS 2
.Os
.Sh NAME
.Nm setgroups
.Nd set group access list
.Sh LIBRARY
.Lb libc
.Sh SYNOPSIS
.In sys/param.h
.In unistd.h
.Ft int
.Fn setgroups "int ngroups" "const gid_t *gidset"
.Sh DESCRIPTION
The
.Fn setgroups
system call
sets the group access list of the current user process
according to the array
.Fa gidset .
The
.Fa ngroups
argument
indicates the number of entries in the array and must be no
more than
.Dv {NGROUPS_MAX}+1 .
.Pp
Only the super-user may set a new group list.
.Pp
The first entry of the group array
.Pq Va gidset[0]
is used as the effective group-ID for the process.
This entry is over-written when a setgid program is run.
To avoid losing access to the privileges of the
.Va gidset[0]
entry, it should be duplicated later in the group array.
By convention,
this happens because the group value indicated
in the password file also appears in
.Pa /etc/group .
The group value in the password file is placed in
.Va gidset[0]
and that value then gets added a second time when the
.Pa /etc/group
file is scanned to create the group set.
.Sh RETURN VALUES
.Rv -std setgroups
.Sh ERRORS
The
.Fn setgroups
system call will fail if:
.Bl -tag -width Er
.It Bq Er EPERM
The caller is not the super-user.
.It Bq Er EINVAL
The number specified in the
.Fa ngroups
argument is larger than the
.Dv {NGROUPS_MAX}+1
limit.
.It Bq Er EFAULT
The address specified for
.Fa gidset
is outside the process
address space.
.El
.Sh SEE ALSO
.Xr getgroups 2 ,
.Xr initgroups 3
.Sh HISTORY
The
.Fn setgroups
system call appeared in
.Bx 4.2 .
BSD 4.4 Lite Lib Sources 1994-05-27 05:00:24 +00:00			`.\" Copyright (c) 1983, 1991, 1993, 1994`
			`.\" The Regents of the University of California. All rights reserved.`
			`.\"`
			`.\" Redistribution and use in source and binary forms, with or without`
			`.\" modification, are permitted provided that the following conditions`
			`.\" are met:`
			`.\" 1. Redistributions of source code must retain the above copyright`
			`.\" notice, this list of conditions and the following disclaimer.`
			`.\" 2. Redistributions in binary form must reproduce the above copyright`
			`.\" notice, this list of conditions and the following disclaimer in the`
			`.\" documentation and/or other materials provided with the distribution.`
Renumber copyright clause 4 Renumber cluase 4 to 3, per what everybody else did when BSD granted them permission to remove clause 3. My insistance on keeping the same numbering for legal reasons is too pedantic, so give up on that point. Submitted by: Jan Schaumann <jschauma@stevens.edu> Pull Request: https://github.com/freebsd/freebsd/pull/96 2017-02-28 23:42:47 +00:00			`.\" 3. Neither the name of the University nor the names of its contributors`
BSD 4.4 Lite Lib Sources 1994-05-27 05:00:24 +00:00			`.\" may be used to endorse or promote products derived from this software`
			`.\" without specific prior written permission.`
			`.\"`
			.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
			`.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE`
			`.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE`
			`.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE`
			`.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL`
			`.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS`
			`.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)`
			`.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT`
			`.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY`
			`.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF`
			`.\" SUCH DAMAGE.`
			`.\"`
Update .Dd missed in -r328304. Reported by: Bjoern Zeeb (bz) MFC with: 328304 2018-01-24 22:36:21 +00:00			`.Dd January 19, 2018`
BSD 4.4 Lite Lib Sources 1994-05-27 05:00:24 +00:00			`.Dt SETGROUPS 2`
mdoc(7) police: removed HISTORY info from the .Os call. 2001-07-10 13:41:46 +00:00			`.Os`
BSD 4.4 Lite Lib Sources 1994-05-27 05:00:24 +00:00			`.Sh NAME`
			`.Nm setgroups`
			`.Nd set group access list`
Introduce ".Lb" macro to libc manpages. More libraries manpages updates following. 2000-04-21 09:42:15 +00:00			`.Sh LIBRARY`
			`.Lb libc`
BSD 4.4 Lite Lib Sources 1994-05-27 05:00:24 +00:00			`.Sh SYNOPSIS`
mdoc(7) police: Use the new .In macro for #include statements. 2001-10-01 16:09:29 +00:00			`.In sys/param.h`
			`.In unistd.h`
BSD 4.4 Lite Lib Sources 1994-05-27 05:00:24 +00:00			`.Ft int`
			`.Fn setgroups "int ngroups" "const gid_t *gidset"`
			`.Sh DESCRIPTION`
mdoc(7) police: Tidy up the syscall language. Stop calling system calls "function calls". Use "The .Fn system call" a-la "The .Nm utility". When referring to a non-BSD implementation in the HISTORY section, call syscall a function, to be safe. 2002-12-18 09:22:32 +00:00			`The`
			`.Fn setgroups`
			`system call`
BSD 4.4 Lite Lib Sources 1994-05-27 05:00:24 +00:00			`sets the group access list of the current user process`
			`according to the array`
			`.Fa gidset .`
mdoc(7) police: "The .Fa argument.". 2002-12-19 09:40:28 +00:00			`The`
BSD 4.4 Lite Lib Sources 1994-05-27 05:00:24 +00:00			`.Fa ngroups`
mdoc(7) police: "The .Fa argument.". 2002-12-19 09:40:28 +00:00			`argument`
BSD 4.4 Lite Lib Sources 1994-05-27 05:00:24 +00:00			`indicates the number of entries in the array and must be no`
			`more than`
In preparation for raising NGROUPS and NGROUPS_MAX, change base system callers of getgroups(), getgrouplist(), and setgroups() to allocate buffers dynamically. Specifically, allocate a buffer of size sysconf(_SC_NGROUPS_MAX)+1 (+2 in a few cases to allow for overflow). This (or similar gymnastics) is required for the code to actually follow the POSIX.1-2008 specification where {NGROUPS_MAX} may differ at runtime and where getgroups may return {NGROUPS_MAX}+1 results on systems like FreeBSD which include the primary group. In id(1), don't pointlessly add the primary group to the list of all groups, it is always the first result from getgroups(). In principle the old code was more portable, but this was only done in one of the two places where getgroups() was called to the overall effect was pointless. Document the actual POSIX requirements in the getgroups(2) and setgroups(2) manpages. We do not yet support a dynamic NGROUPS, but we may in the future. MFC after: 2 weeks 2009-06-19 15:58:24 +00:00			`.Dv {NGROUPS_MAX}+1 .`
BSD 4.4 Lite Lib Sources 1994-05-27 05:00:24 +00:00			`.Pp`
Make it clearer that privilege is needed to reduce as well as increase group membership. 2008-06-16 14:50:21 +00:00			`Only the super-user may set a new group list.`
In the C library, the setting up of the group array by various utilities is done by calling gr_addgid() for each group to be added (usually found by traversing /etc/group) then calling the setgroups() system call after the group set has been created. The gr_addgid() function (helpfully?) deduplicates the addition of group members. So, if you call it to add a group member that already exists, it is just dropped. Because group[0] is the effective group-ID and is over-written when a setgid program is run, The value in group[0] is usually duplicated so that group value is not lost when a setgid program is run. Historically this happened because the group value indicated in the password file also appears in /etc/group (e.g., if you are group staff in the password file, you will also appear in the staff line in /etc/group). But, with the addition of the deduplication, the attempt to add group staff was lost because it already appeared in group[0]. So, the fix is to deduplicate starting from group[1] which allows a duplicate of the entry in group[0], but not in later entries. There is some confusion about the setgroups system call because in BSD it has (always) set the entire group including the egid group (in group[0]). However, in Linux, it skips over group[0] and starts setting from group[1]. See this comment from linux_setgroups: /* * cr_groups[0] holds egid. Setting the whole set from * the supplied set will cause egid to be changed too. * Keep cr_groups[0] unchanged to prevent that. */ To make it clear what the BSD setgroups system call does, I added the following paragraph to the setgroups(2) manual page: The first entry of the group array (gidset[0]) is used as the effective group-ID for the process. This entry is over-written when a setgid program is run. To avoid losing access to the privileges of the gidset[0] entry, it should be duplicated later in the group array. By convention, this happens because the group value indicated in the password file also appears in /etc/group. The group value in the password file is placed in gidset[0] and that value then gets added a second time when the /etc/group file is scanned to create the group set. Reported by: Paul McMath paulm at tetrardus.net Reviewed by: kib MFC after: 2 weeks 2018-01-23 22:18:45 +00:00			`.Pp`
			`The first entry of the group array`
			`.Pq Va gidset[0]`
			`is used as the effective group-ID for the process.`
			`This entry is over-written when a setgid program is run.`
			`To avoid losing access to the privileges of the`
			`.Va gidset[0]`
			`entry, it should be duplicated later in the group array.`
			`By convention,`
			`this happens because the group value indicated`
			`in the password file also appears in`
			`.Pa /etc/group .`
			`The group value in the password file is placed in`
			`.Va gidset[0]`
			`and that value then gets added a second time when the`
			`.Pa /etc/group`
			`file is scanned to create the group set.`
BSD 4.4 Lite Lib Sources 1994-05-27 05:00:24 +00:00			`.Sh RETURN VALUES`
Use the ``.Rv -std'' mdoc(7) macro in appropriate cases. Reviewed by: ru 2001-08-09 13:32:13 +00:00			`.Rv -std setgroups`
BSD 4.4 Lite Lib Sources 1994-05-27 05:00:24 +00:00			`.Sh ERRORS`
			`The`
			`.Fn setgroups`
mdoc(7) police: Tidy up the syscall language. Stop calling system calls "function calls". Use "The .Fn system call" a-la "The .Nm utility". When referring to a non-BSD implementation in the HISTORY section, call syscall a function, to be safe. 2002-12-18 09:22:32 +00:00			`system call will fail if:`
BSD 4.4 Lite Lib Sources 1994-05-27 05:00:24 +00:00			`.Bl -tag -width Er`
			`.It Bq Er EPERM`
			`The caller is not the super-user.`
Documented missing EINVAL errno value kern_prot.c: if (ngrp > NGROUPS) return (EINVAL); MFC after: 2 weeks 2003-11-19 13:05:50 +00:00			`.It Bq Er EINVAL`
			`The number specified in the`
			`.Fa ngroups`
			`argument is larger than the`
In preparation for raising NGROUPS and NGROUPS_MAX, change base system callers of getgroups(), getgrouplist(), and setgroups() to allocate buffers dynamically. Specifically, allocate a buffer of size sysconf(_SC_NGROUPS_MAX)+1 (+2 in a few cases to allow for overflow). This (or similar gymnastics) is required for the code to actually follow the POSIX.1-2008 specification where {NGROUPS_MAX} may differ at runtime and where getgroups may return {NGROUPS_MAX}+1 results on systems like FreeBSD which include the primary group. In id(1), don't pointlessly add the primary group to the list of all groups, it is always the first result from getgroups(). In principle the old code was more portable, but this was only done in one of the two places where getgroups() was called to the overall effect was pointless. Document the actual POSIX requirements in the getgroups(2) and setgroups(2) manpages. We do not yet support a dynamic NGROUPS, but we may in the future. MFC after: 2 weeks 2009-06-19 15:58:24 +00:00			`.Dv {NGROUPS_MAX}+1`
Documented missing EINVAL errno value kern_prot.c: if (ngrp > NGROUPS) return (EINVAL); MFC after: 2 weeks 2003-11-19 13:05:50 +00:00			`limit.`
BSD 4.4 Lite Lib Sources 1994-05-27 05:00:24 +00:00			`.It Bq Er EFAULT`
			`The address specified for`
			`.Fa gidset`
			`is outside the process`
			`address space.`
			`.El`
			`.Sh SEE ALSO`
			`.Xr getgroups 2 ,`
			`.Xr initgroups 3`
			`.Sh HISTORY`
			`The`
Correctly use .Fn instead of .Nm to reference function names in a bunch of man pages. Use the correct .Bx (BSD UNIX) or .At (AT&T UNIX) macros instead of explicitly specifying the version in the text in a bunch of man pages. 1996-08-22 23:31:07 +00:00			`.Fn setgroups`
mdoc(7) police: Tidy up the syscall language. Stop calling system calls "function calls". Use "The .Fn system call" a-la "The .Nm utility". When referring to a non-BSD implementation in the HISTORY section, call syscall a function, to be safe. 2002-12-18 09:22:32 +00:00			`system call appeared in`
BSD 4.4 Lite Lib Sources 1994-05-27 05:00:24 +00:00			`.Bx 4.2 .`