2015-09-18 21:35 GMT+02:00 J. Bruce Fields <bfields@xxxxxxxxxxxx>:
> 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?
Inheritable everyone@ allow entries at the end of the ACL are not
uncommon. This special case prevents the algorithm from splitting such
entries into inherit-only and non-inheritable parts.
> 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....
Great to hear that :)
Thanks,
Andreas
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