Re: [uml-devel] hostfs as root

[Michael Richardson <mcr@sandelman.ottawa.on.ca>]

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>>>>> "Matt" == Matt Zimmerman <mdz@debian.org> writes:
    >> okay.. Makes sense. But, since they are mode 0, we can't open them as
    >> the user, which root inside could do. Is there some compromise that we
    >> can 
    >> do until we have the permissions layer in place?
    >> Like, forcing u+r on the underlying file maybe? 

    Matt> The problem I ran into which led me to this bug was extracting tar
    Matt> archives. 
    Matt> When they contain read-only files, tar opens them for writing with
    Matt> read-only 
    Matt> permissions.  Since UML was creating the file and then, subsequently,
    Matt> attempting to open it for writing, the second open failed.

  How is this the correct thing to do for the UML then?
  What bug did you uncover?

    Matt> I think that in general, having the permissions silently changed
    Matt> would be 
    Matt> unwise, though I admit that u-r permissions are weird at best.  It

  Well, if the opener is root, you get to ignore the permissions. That means
that something has to break.

  I propose:
    stat(), save permissions
    chmod(u+rw) (as appropriate for the open)
    open()
    chmod(oldperms)

    Matt> would 
    Matt> seem better to have mount fixed to stop doing this strange thing, and
    Matt> eventually to emulate full permission control in hostfs.

  Well, leaving us in a lurch is decidely not friendly.  
  Your fix has broken debian potato's mount. Being able to run other distros,
versions, etc. inside of UML is one of the major features of UML.

]      Out and about in Ottawa.    hmmm... beer.                |  firewalls  [
]   Michael Richardson, Sandelman Software Works, Ottawa, ON    |net architect[
] mcr@sandelman.ottawa.on.ca http://www.sandelman.ottawa.on.ca/ |device driver[
] panic("Just another Debian/notebook using, kernel hacking, security guy");  [

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