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On most other platforms observed, including OpenBSD, NetBSD, and Linux,
these system calls have long since been converted to only touching the
supplementary groups of the process. This poses both portability and
security concerns in porting software to and from FreeBSD, as this
subtle difference is a landmine waiting to happen. Bugs have been
discovered even in FreeBSD-local sources, since this behavior is
somewhat unintuitive (see, e.g., fix 48fd05999b for chroot(8)).
Now that the egid is tracked outside of cr_groups in our ucred, convert
the syscalls to deal with only supplementary groups. Some remaining
stragglers in base that had baked in assumptions about these syscalls
are fixed in the process to avoid heartburn in conversion.
For relnotes: application developers should audit their use of both
setgroups(2) and getgroups(2) for signs that they had assumed the
previous FreeBSD behavior of using the first element for the egid. Any
calls to setgroups() to clear groups that used a single array of the
now or soon-to-be egid can be converted to setgroups(0, NULL) calls to
clear the supplementary groups entirely on all FreeBSD versions.
Co-authored-by: olce (but bugs are likely mine)
Relnotes: yes (see last paragraph)
Reviewed by: kib
Differential Revision: https://reviews.freebsd.org/D51648
111 lines
3.2 KiB
Groff
111 lines
3.2 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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.\" 3. 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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.Dd August 1, 2025
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.Dt GETGROUPS 2
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.Os
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.Sh NAME
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.Nm getgroups
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.Nd get group access list
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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 getgroups "int gidsetlen" "gid_t *gidset"
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.Sh DESCRIPTION
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The
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.Fn getgroups
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system call
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gets the current supplementary groups of the user process and stores it in the
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array
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.Fa gidset .
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The
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.Fa gidsetlen
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argument
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indicates the number of entries that may be placed in
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.Fa gidset .
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The
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.Fn getgroups
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system call
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returns the actual number of groups returned in
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.Fa gidset .
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As many as {NGROUPS_MAX} values may be returned.
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If
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.Fa gidsetlen
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is zero,
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.Fn getgroups
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returns the number of supplementary group IDs associated with
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the calling process without modifying the array pointed to by
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.Fa gidset .
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.Pp
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The value of
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.Dv {NGROUPS_MAX}
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should be obtained using
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.Xr sysconf 3
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to avoid hard-coding it into the executable.
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.Sh RETURN VALUES
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A successful call returns the number of groups in the group set.
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A value of -1 indicates that an error occurred, and the error
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code is stored in the global variable
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.Va errno .
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.Sh ERRORS
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The possible errors for
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.Fn getgroups
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are:
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.Bl -tag -width Er
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.It Bq Er EINVAL
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The argument
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.Fa gidsetlen
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is smaller than the number of groups in the group set.
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.It Bq Er EFAULT
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The argument
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.Fa gidset
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specifies
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an invalid address.
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.El
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.Sh SEE ALSO
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.Xr setgroups 2 ,
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.Xr initgroups 3 ,
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.Xr sysconf 3
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.Sh STANDARDS
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The
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.Fn getgroups
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system call conforms to
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.St -p1003.1-2008 .
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.Sh HISTORY
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The
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.Fn getgroups
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system call appeared in
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.Bx 4.2 .
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.Pp
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Before
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.Fx 15.0 ,
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the
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.Fn getgroups
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system call always returned the effective group ID for the process as the first
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element of the array, before the supplementary groups.
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