Re: [PATCH] Introduce BSD-style user credential [3/3]

[Trond Myklebust <trond.myklebust@fys.uio.no>]

>>>>> " " == Linus Torvalds <torvalds@transmeta.com> writes:

     > On Sat, 31 Aug 2002, Trond Myklebust wrote:
    >>
    >> task-> ucred is not the unit for implementing shared creds
    >> between threads.

     > Fair enough, but some solution to this has to be found. I do
     > not want to apply something that simply cannot work sanely, and
     > I want to have at least a _plan_ on the table.

The plan is pretty rough at the moment, and not all of the code has
been written yet. Basically, it boils down to:

  Add the COW structure 'vfs_cred'

  Make VFS changes to replace all instances of
  current->fsuid/fsgid/ngroups/groups with a single 'vfs_cred' that
  never can be changed by CLONE_CRED after we call down into the VFS.
  This means that we have to actually invent mechanisms for passing
  those creds down to address_space_operations, inode_operations.

  Add the more volatile 'pcred' a.k.a. 'task_cred' (see below), which
  forms the necessary basis for CLONE_CRED tasks.

  Audit 'task_cred' to ensure that CLONE_CRED won't introduce new
  security holes. Things like capabilities, which can sometimes
  override 'standard credentials', will for instance need to be looked
  into.

  .... end of process -> add CLONE_CRED flag to 'clone()'

     > This really ties in with the patches Dave has done (which are
     > equivalent to your "pcred"), and I'd like to see them work
     > together in practice.

Dave and I have already been discussing this on l-k, and we appear now
to be in agreement on general procedure. Dave has said that he'd like
to contribute once we get vfs_cred well established. I'm hoping he'll
help out on the latter too ;-)

     > (I would suggest calling the FS credentials "struct vfs_cred",
     > while the regular user credentials might just be "struct cred".
     > Other suggestions?)

I'm fine about 'vfs'cred', but how about 'struct task_cred' instead
for the second? That ties them directly in to the task_struct, and
avoids people mistaking for 'ucred'. Since the distinction between COW
and non-COW is pretty profound, it might be useful in order to help
emphasize to which category they belong...

Cheers,
   Trond