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    SubjectRe: [RFC v7 26/41] richacl: Apply the file masks to a richacl
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    On Sat, Sep 05, 2015 at 12:27:21PM +0200, Andreas Gruenbacher wrote:
    > Put all the pieces of the acl transformation puzzle together for
    > computing a richacl which has the file masks "applied" so that the
    > standard nfsv4 access check algorithm can be used on the richacl.
    >
    > Signed-off-by: Andreas Gruenbacher <agruen@kernel.org>
    > ---
    > fs/richacl_compat.c | 110 ++++++++++++++++++++++++++++++++++++++++++++++++
    > include/linux/richacl.h | 3 ++
    > 2 files changed, 113 insertions(+)
    >
    > diff --git a/fs/richacl_compat.c b/fs/richacl_compat.c
    > index 412844c..9681efe 100644
    > --- a/fs/richacl_compat.c
    > +++ b/fs/richacl_compat.c
    > @@ -730,3 +730,113 @@ richacl_isolate_group_class(struct richacl_alloc *alloc)
    > }
    > return 0;
    > }
    > +
    > +/**
    > + * __richacl_apply_masks - apply the file masks to all aces
    > + * @alloc: acl and number of allocated entries
    > + *
    > + * Apply the owner mask to owner@ aces, the other mask to
    > + * everyone@ aces, and the group mask to all other aces.
    > + *
    > + * The previous transformations have brought the acl into a
    > + * form in which applying the masks will not lead to the
    > + * accidental loss of permissions anymore.
    > + */
    > +static int
    > +__richacl_apply_masks(struct richacl_alloc *alloc, kuid_t owner)
    > +{
    > + struct richace *ace;
    > +
    > + richacl_for_each_entry(ace, alloc->acl) {
    > + unsigned int mask;
    > +
    > + if (richace_is_inherit_only(ace) || !richace_is_allow(ace))
    > + continue;
    > + if (richace_is_owner(ace) ||
    > + (richace_is_unix_user(ace) && uid_eq(owner, ace->e_id.uid)))
    > + mask = alloc->acl->a_owner_mask;

    Is treating matching user aces like owner aces what you intended to do,
    and if so, why?

    --b.

    > + else if (richace_is_everyone(ace))
    > + mask = alloc->acl->a_other_mask;
    > + else
    > + mask = alloc->acl->a_group_mask;
    > + if (richace_change_mask(alloc, &ace, ace->e_mask & mask))
    > + return -1;
    > + }
    > + return 0;
    > +}
    > +
    > +/**
    > + * richacl_apply_masks - apply the masks to the acl
    > + *
    > + * Transform @acl so that the standard NFSv4 permission check algorithm (which
    > + * is not aware of file masks) will compute the same access decisions as the
    > + * richacl permission check algorithm (which looks at the acl and the file
    > + * masks).
    > + *
    > + * This algorithm is split into several steps:
    > + *
    > + * - Move everyone@ aces to the end of the acl. This simplifies the other
    > + * transformations, and allows the everyone@ allow ace at the end of the
    > + * acl to eventually allow permissions to the other class only.
    > + *
    > + * - Propagate everyone@ permissions up the acl. This transformation makes
    > + * sure that the owner and group class aces won't lose any permissions when
    > + * we apply the other mask to the everyone@ allow ace at the end of the acl.
    > + *
    > + * - Apply the file masks to all aces.
    > + *
    > + * - Make sure the owner is granted the owner mask permissions.
    > + *
    > + * - Make sure everyone is granted the other mask permissions.
    > + *
    > + * - Make sure that the owner is not granted any permissions beyond the owner
    > + * mask from group class aces or from everyone@.
    > + *
    > + * - Make sure that the group class is not granted any permissions from
    > + * everyone@.
    > + *
    > + * The algorithm is exact except for richacls which cannot be represented as an
    > + * acl alone: for example, given this acl:
    > + *
    > + * group@:rw::allow
    > + *
    > + * when file masks corresponding to mode 0600 are applied, the owner would only
    > + * get rw access if he is a member of the owning group. This algorithm would
    > + * produce an empty acl in this case. We fix this case by modifying
    > + * richacl_permission() so that the group mask is always applied to group class
    > + * aces. With this fix, the owner would not have any access (beyond the
    > + * implicit permissions always granted to owners).
    > + *
    > + * NOTE: Depending on the acl and file masks, this algorithm can increase the
    > + * number of aces by almost a factor of three in the worst case. This may make
    > + * the acl too large for some purposes.
    > + */
    > +int
    > +richacl_apply_masks(struct richacl **acl, kuid_t owner)
    > +{
    > + if ((*acl)->a_flags & RICHACL_MASKED) {
    > + struct richacl_alloc alloc = {
    > + .acl = richacl_clone(*acl, GFP_KERNEL),
    > + .count = (*acl)->a_count,
    > + };
    > + if (!alloc.acl)
    > + return -ENOMEM;
    > +
    > + if (richacl_move_everyone_aces_down(&alloc) ||
    > + richacl_propagate_everyone(&alloc) ||
    > + __richacl_apply_masks(&alloc, owner) ||
    > + richacl_set_owner_permissions(&alloc) ||
    > + richacl_set_other_permissions(&alloc) ||
    > + richacl_isolate_owner_class(&alloc) ||
    > + richacl_isolate_group_class(&alloc)) {
    > + richacl_put(alloc.acl);
    > + return -ENOMEM;
    > + }
    > +
    > + alloc.acl->a_flags &= ~(RICHACL_WRITE_THROUGH | RICHACL_MASKED);
    > + richacl_put(*acl);
    > + *acl = alloc.acl;
    > + }
    > + return 0;
    > +}
    > +EXPORT_SYMBOL_GPL(richacl_apply_masks);
    > diff --git a/include/linux/richacl.h b/include/linux/richacl.h
    > index 832b06c..a945f3c 100644
    > --- a/include/linux/richacl.h
    > +++ b/include/linux/richacl.h
    > @@ -332,4 +332,7 @@ extern struct richacl *richacl_inherit(const struct richacl *, int);
    > extern int richacl_permission(struct inode *, const struct richacl *, int);
    > extern struct richacl *richacl_create(struct inode *, struct inode *);
    >
    > +/* richacl_compat.c */
    > +extern int richacl_apply_masks(struct richacl **, kuid_t);
    > +
    > #endif /* __RICHACL_H */
    > --
    > 2.4.3
    >
    > --
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