kern/57246: NFS group permissions regression

[mark%ecs.vuw.ac.nz@localhost]

>Number:         57246
>Category:       kern
>Synopsis:       NFS group permissions regression
>Confidential:   no
>Severity:       critical
>Priority:       high
>Responsible:    kern-bug-people
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Sun Feb 26 23:00:00 +0000 2023
>Originator:     Mark Davies
>Release:        NetBSD 10.0_BETA
>Organization:
ECS, Victoria Uni. of Wellington, New Zealand.
>Environment:
	
	
System: NetBSD turakirae.ecs.vuw.ac.nz 10.0_BETA NetBSD 10.0_BETA (GENERIC) #1: Thu Jan 26 11:09:32 NZDT 2023 mark%turakirae.ecs.vuw.ac.nz@localhost:/local/SAVE/10_64.obj/src/work/10/src/sys/arch/amd64/compile/GENERIC amd64
Architecture: x86_64
Machine: amd64
>Description:
        On a linux system, mounting from a NetBSD 10.0_BETA, files that should be writeable
 	over NFS due to group permissions fail, and
	lose their current contents.

>How-To-Repeat:

	On a linux system, mounting from a NetBSD 10.0_BETA
	In an NFS mounted file system, create two files - one owned by you, the other
	owned by someone else but with group permissions giving you write access.  Try
	copying first file to second.  Get error and the second file is zeroed.

	city-art% df -h .
	Filesystem               Size  Used Avail Use% Mounted on
	lido:/am/lido/home/mark  2.0T  1.1T  813G  58% /home/mark
	city-art% groups mark
	root src docker msor programmers tech ecs
	city-art% ls -la
	total 40
	drwxr-xr-x   2 mark ecs   512 Feb 27 09:40 .
	drwxr-x--x 324 mark ecs 27136 Feb 27 11:32 ..
	-rw-rw-r--   1 mark ecs     6 Feb 27 09:40 A
	-rw-rw-r--   1 www  ecs     8 Feb 27 09:40 B
	city-art% cp A B
	cp: cannot create regular file 'B': Permission denied
	city-art% ls -la
	total 36
	drwxr-xr-x   2 mark ecs   512 Feb 27 09:40 .
	drwxr-x--x 324 mark ecs 27136 Feb 27 11:32 ..
	-rw-rw-r--   1 mark ecs     6 Feb 27 09:40 A
	-rw-rw-r--   1 www  ecs     0 Feb 27 09:42 B


	Doing this from NetBSD to NetBSD works
	Doing this from linux to NetBSD 9.3_STABLE works

	
>Fix:
	No idea, would love one
	

>Unformatted: