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Re: Permission Questions

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On Mon, Aug 30, 2021 at 10:57:59PM +0200, Rainer Dorsch wrote:
> Hmm...your example works for me as well
> 
> rd@h370:~/tmp.nobackup$ sudo touch /tmp/123; sudo chgrp video /tmp/123; sudo 
> chmod 664 /tmp/123
> [sudo] Passwort für rd: 
> rd@h370:~/tmp.nobackup$ ls -l /tmp/123
> -rw-rw-r-- 1 root video 0 30. Aug 22:52 /tmp/123
> rd@h370:~/tmp.nobackup$ id
> uid=2809(rd) gid=2809(rd) Gruppen=2809(rd),4(adm),20(dialout),21(fax),
> 24(cdrom),25(floppy),27(sudo),30(dip),44(video),46(plugdev),100(users),
> 114(lpadmin),118(scanner),126(docker),127(vboxusers),130(i2psvc),
> 131(wireshark),141(libvirt),1000(sispmctl)
> rd@h370:~/tmp.nobackup$ echo stuff >> /tmp/123
> rd@h370:~/tmp.nobackup$ 
> 
> As soon as I do a chown to a non-root user on /tmp/123 it does not work for me 
> anymore.
> 
> Is root somehow treated differently as other users?

unicorn:~$ ls -l /tmp/123
-rw-rw-r-- 1 daemon video 0 Aug 30 17:00 /tmp/123
unicorn:~$ echo stuff >> /tmp/123
bash: /tmp/123: Permission denied

That is interesting!

unicorn:~$ strace bash -c 'echo stuff >> /tmp/123'
[...]
openat(AT_FDCWD, "/tmp/123", O_WRONLY|O_CREAT|O_APPEND, 0666) = -1 EACCES (Permission denied)

As far as I can see, this is a kernel bug.  Unless I'm overlooking
something...?

For fun, I also tried it with the primary group:

unicorn:~$ id
uid=1000(greg) gid=1000(greg) groups=1000(greg),24(cdrom),25(floppy),27(sudo),29(audio),30(dip),44(video),46(plugdev),108(netdev)
unicorn:~$ sudo chgrp 1000 /tmp/123
unicorn:~$ echo stuff >> /tmp/123
bash: /tmp/123: Permission denied
unicorn:~$ ls -l /tmp/123
-rw-rw-r-- 1 daemon greg 0 Aug 30 17:00 /tmp/123

So it's not just the secondary group that's causing it.

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Permission Questions Rainer Dorsch <ml@bokomoko.de> - 2021-08-30 21:50 +0200
  Re: Permission Questions Greg Wooledge <greg@wooledge.org> - 2021-08-30 22:00 +0200
    Re: Permission Questions Rainer Dorsch <ml@bokomoko.de> - 2021-08-30 23:00 +0200
      Re: Permission Questions Greg Wooledge <greg@wooledge.org> - 2021-08-30 23:10 +0200
        Re: Permission Questions Andy Smith <andy@strugglers.net> - 2021-08-30 23:30 +0200
          Re: Permission Questions Greg Wooledge <greg@wooledge.org> - 2021-08-31 00:10 +0200
            Re: Permission Questions Rainer Dorsch <ml@bokomoko.de> - 2021-08-31 11:00 +0200
  Re: Permission Questions IL Ka <kazakevichilya@gmail.com> - 2021-08-30 22:00 +0200

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