Re: kern/56232: Unstable system with tar on /dev

[David Holland <dholland-bugs%netbsd.org@localhost>]

The following reply was made to PR kern/56232; it has been noted by GNATS.

From: David Holland <dholland-bugs%netbsd.org@localhost>
To: gnats-bugs%netbsd.org@localhost
Cc: 
Subject: Re: kern/56232: Unstable system with tar on /dev
Date: Fri, 4 Jun 2021 16:42:54 +0000

 On Fri, Jun 04, 2021 at 08:25:01AM +0000, Martin Husemann wrote:
  >  We had this discussion before, I think there even is an open PR
  >  against tar.
  >  Folks are in eiteher of two camps:
  >  
  >   - tar needs to open the file and extract ACLs from the filedescriptor,
  >     otherwise there would be races.
  >  
  >      -> solution: the kernel should never do state changes (like rewind
  >         tapes or similar) on plain "open" of a device node
  >  
  >   - tar should avoid all this dance when there are no ACLs anyway on the
  >     file system it is traversing. State changes on device open may be a
  >     hack, but they are a very ancient unix hack and quite common.
 
 Devices with side-effecting open are a thing; they aren't going to go
 away. Volumes with ACLs are also a thing, and might reasonably include
 the root fs, and in fact devices are one of the things you might
 specifically want custom access control for.
 
 Conclusion: tar (and other things) need to be able to fetch acls
 without open().
 
 Do you remember where this discussion was, or some search keywords? My
 gnats index is not what it used to be.
 
  >  There is an option to tar (I forgot which) to not backup ACLs - and then 
  >  everything should be fine.
  >  
  >  IMHO this option should be on by default.
 
 Silently throwing away your ACLs in your backups isn't the right
 answer either :-(
 
 -- 
 David A. Holland
 dholland%netbsd.org@localhost