diff options
Diffstat (limited to 'lib/libc/gen/initgroups.3')
| -rw-r--r-- | lib/libc/gen/initgroups.3 | 101 |
1 files changed, 86 insertions, 15 deletions
diff --git a/lib/libc/gen/initgroups.3 b/lib/libc/gen/initgroups.3 index 03bd07494fc9..4f538fb180ec 100644 --- a/lib/libc/gen/initgroups.3 +++ b/lib/libc/gen/initgroups.3 @@ -1,5 +1,13 @@ +.\"- +.\" SPDX-License-Identifier: BSD-3-Clause +.\" .\" Copyright (c) 1983, 1991, 1993 .\" The Regents of the University of California. All rights reserved. +.\" Copyright (c) 2025 The FreeBSD Foundation +.\" +.\" Portions of this documentation were written by Olivier Certner +.\" <olce@FreeBSD.org> at Kumacom SARL under sponsorship from the FreeBSD +.\" Foundation. .\" .\" Redistribution and use in source and binary forms, with or without .\" modification, are permitted provided that the following conditions @@ -25,12 +33,12 @@ .\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF .\" SUCH DAMAGE. .\" -.Dd October 26, 2014 +.Dd September 17, 2025 .Dt INITGROUPS 3 .Os .Sh NAME .Nm initgroups -.Nd initialize group access list +.Nd initialize supplementary groups as per the group database .Sh LIBRARY .Lb libc .Sh SYNOPSIS @@ -40,19 +48,18 @@ .Sh DESCRIPTION The .Fn initgroups -function -uses the -.Xr getgrouplist 3 -function to calculate the group access list for the user -specified in +function initializes the current process' supplementary groups as prescribed by +its arguments and the system's group database. +.Pp +It first uses the +.Fn getgrouplist +function to compute a list of groups containing the passed +.Fa basegid , +which typically is the user's initial numerical group ID from the password +database, and the supplementary groups in the group database for the user named .Fa name . -This group list is then setup for the current process using -.Xr setgroups 2 . -The -.Fa basegid -is automatically included in the groups list. -Typically this value is given as -the group number from the password file. +It then installs this list as the current process' supplementary groups using +.Fn setgroups . .Sh RETURN VALUES .Rv -std initgroups .Sh ERRORS @@ -60,7 +67,7 @@ The .Fn initgroups function may fail and set .Va errno -for any of the errors specified for the library function +to any of the errors specified for the library function .Xr setgroups 2 . It may also return: .Bl -tag -width Er @@ -77,3 +84,67 @@ The .Fn initgroups function appeared in .Bx 4.2 . +.Pp +The +.Fn initgroups +function changed semantics in +.Fx 15 , +following that of +.Xr setgroups 2 +in the same release. +Before that, it would also set the effective group ID to +.Fa basegid , +and would not include the latter in the supplementary groups except before +.Fx 8 . +Its current behavior in these respects is known to be compatible with that of +the following systems up to the specified versions that are current at time of +this writing: +.Bl -dash -width "-" -compact +.It +Linux (up to 6.6) with the GNU libc (up to 2.42) +.It +.Nx 1.1 and greater (up to 10) +.It +.Ox (up to 7.7) +.It +Systems based on illumos (up to August 2025 sources) +.El +.Sh SECURITY CONSIDERATIONS +As +.Fa basegid +is typically the user's initial numerical group ID, to which the current +process' effective group ID is generally initialized, processes using functions +to change their effective group ID +.Pq via Xr setgid 2 or similar +or that are spawned from executables with the set-group-ID mode bit set will not +be able to relinquish the access rights deriving from being a member of +.Fa basegid , +as these functions do not change the supplementary groups. +.Pp +This behavior is generally desirable in order to paper over the difference of +treatment between the effective group and supplementary ones in this situation, +as they are all in the end indiscriminately used in traditional UNIX +discretionary access checks. +It blends well with the practice of allocating each user its own private group, +as processes launched from a set-group-ID executable keep the same user and +consistently stay also in the same user's group. +Finally, it was also chosen for compatibility with other systems +.Po +see the +.Sx HISTORY +section +.Pc . +.Pp +This convention of including +.Fa basegid +in the supplementary groups is however only enforced by the +.Fn initgroups +function, and not by the +.Xr setgroups 2 +system call, so applications expressly wanting to include in the supplementary +groups only those specified by the group database can themselves call +.Fn getgrouplist +and then +.Fn setgroups +on the result with the first element skipped +.Pq see Xr getgrouplist 3 . |