On Sat, Sep 05, 2015 at 12:27:16PM +0200, Andreas Gruenbacher wrote:
> The POSIX standard puts processes which are not the owner or a member in
> the owning group or which match any ace other then everyone@ on the
> other file class. We only know if a process is in the other class after
> processing the entire acl.
>
> Move all everyone@ aces in the acl down in the acl so that at most a
> single everyone@ allow ace remains at the end. Permissions which are
> not explicitly allowed are implicitly denied, so an everyone@ deny ace
> is unneeded.
>
> The everyone@ aces can be moved down the acl without changing the
> permissions that the acl grants. This transformation simplifies the
> following algorithms, and eventually allows us to turn the final
> everyone@ allow ace into an entry for the other class.
>
> Signed-off-by: Andreas Gruenbacher <agruen@xxxxxxxxxx>
> ---
> fs/richacl_compat.c | 65 +++++++++++++++++++++++++++++++++++++++++++++++++++++
> 1 file changed, 65 insertions(+)
>
> diff --git a/fs/richacl_compat.c b/fs/richacl_compat.c
> index 341e429..4f0acf5 100644
> --- a/fs/richacl_compat.c
> +++ b/fs/richacl_compat.c
> @@ -153,3 +153,68 @@ richace_change_mask(struct richacl_alloc *alloc, struct richace **ace,
> }
> return 0;
> }
> +
> +/**
> + * richacl_move_everyone_aces_down - move everyone@ aces to the end of the acl
> + * @alloc: acl and number of allocated entries
> + *
> + * Move all everyone aces to the end of the acl so that only a single everyone@
> + * allow ace remains at the end, and update the mask fields of all aces on the
> + * way. The last ace of the resulting acl will be an everyone@ allow ace only
> + * if @acl grants any permissions to @everyone. No @everyone deny aces will
> + * remain.
> + *
> + * This transformation does not alter the permissions that the acl grants.
> + * Having at most one everyone@ allow ace at the end of the acl helps us in the
> + * following algorithms.
> + */
> +static int
> +richacl_move_everyone_aces_down(struct richacl_alloc *alloc)
> +{
> + struct richace *ace;
> + unsigned int allowed = 0, denied = 0;
> +
> + richacl_for_each_entry(ace, alloc->acl) {
> + if (richace_is_inherit_only(ace))
> + continue;
> + if (richace_is_everyone(ace)) {
> + if (richace_is_allow(ace))
> + allowed |= (ace->e_mask & ~denied);
> + else if (richace_is_deny(ace))
> + denied |= (ace->e_mask & ~allowed);
> + else
> + continue;
> + if (richace_change_mask(alloc, &ace, 0))
> + return -1;
> + } else {
> + if (richace_is_allow(ace)) {
> + if (richace_change_mask(alloc, &ace, allowed |
> + (ace->e_mask & ~denied)))
> + return -1;
> + } else if (richace_is_deny(ace)) {
> + if (richace_change_mask(alloc, &ace, denied |
> + (ace->e_mask & ~allowed)))
> + return -1;
> + }
> + }
> + }
> + if (allowed & ~RICHACE_POSIX_ALWAYS_ALLOWED) {
> + struct richace *last_ace = ace - 1;
> +
> + if (alloc->acl->a_entries &&
> + richace_is_everyone(last_ace) &&
> + richace_is_allow(last_ace) &&
> + richace_is_inherit_only(last_ace) &&
> + last_ace->e_mask == allowed)
> + last_ace->e_flags &= ~RICHACE_INHERIT_ONLY_ACE;
That's a funny special case! Is it even worth it, or could we just live
with an extra uninheritable EVERYONE ace in this case?
Anyway, again I like the way you've set this all up with the little
acl-editing helpers, it makes this easier to follow than it otherwise
would be....
Reviewed-by: J. Bruce Fields <bfields@xxxxxxxxxx>
--b.
> + else {
> + if (richacl_insert_entry(alloc, &ace))
> + return -1;
> + ace->e_type = RICHACE_ACCESS_ALLOWED_ACE_TYPE;
> + ace->e_flags = RICHACE_SPECIAL_WHO;
> + ace->e_mask = allowed;
> + ace->e_id.special = RICHACE_EVERYONE_SPECIAL_ID;
> + }
> + }
> + return 0;
> +}
> --
> 2.4.3
>
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