kern/54381: cp read-only-file /to/psshfs/ returns EPERM

[tobiasu%tmux.org@localhost]

>Number:         54381
>Category:       kern
>Synopsis:       cp read-only-file /to/psshfs/ returns EPERM
>Confidential:   no
>Severity:       serious
>Priority:       medium
>Responsible:    kern-bug-people
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Tue Jul 16 12:50:00 +0000 2019
>Originator:     Tobias Ulmer
>Release:        NetBSD 8.99.50
>Organization:
>Environment:
NetBSD phenom.tmux.org 8.99.50 NetBSD 8.99.50 (GENERIC) #0: Fri Jul 12 10:39:12 UTC 2019  mkrepro%mkrepro.NetBSD.org@localhost:/usr/src/sys/arch/amd64/compile/GENERIC amd64

>Description:
Copy a user owned read-only file to a user writable psshfs mountpoint like so:

tobiasu@phenom:tobiasu$ ./tfs    
+ rm -f rw ro mnt/rw mnt/ro rw.log ro.log
+ echo rw >rw
+ echo ro >ro
+ chmod 444 ro
+ ktruss cp rw mnt/ >rw.log
+ ktruss cp ro mnt/ >ro.log
cp: mnt/ro: Operation not permitted

huh?

"rw" does what you expect:
1010      1 cp       __stat50("rw", 0x7a15bdb4c1b8) = 0                        
1010      1 cp       __stat50("mnt/rw", 0x7f7fffab5fc0) Err#2 ENOENT          
1010      1 cp       open("rw", 0, 0)            = 3                           
1010      1 cp       open("mnt/rw", 0x601, 0x81b4) = 4


0x81b4 = 0100664

"ro" uses a different file mask:
161      1 cp       __stat50("ro", 0x6fcf05dd21b8) = 0                        
161      1 cp       __stat50("mnt/ro", 0x7f7fff750ca0) Err#2 ENOENT          
161      1 cp       open("ro", 0, 0)            = 3                           
161      1 cp       open("mnt/ro", 0x601, 0x8124) Err#1 EPERM

0x8124 = 0100444
>How-To-Repeat:

>Fix: