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    Subject[PATCH -V3 06/17] richacl: Compute maximum file masks from an acl
    Date
    From: Andreas Gruenbacher <agruen@suse.de>

    Compute upper bound owner, group, and other file masks with as few
    permissions as possible without denying any permissions that the NFSv4
    acl in a richacl grants.

    This algorithm is used when a file inherits an acl at create time and
    when an acl is set via a mechanism that does not specify file modes
    (such as via nfsd). When user-space sets an acl, the file masks are
    passed in as part of the xattr.

    When setting a richacl, the file masks determine what the file
    permission bits will be set to; see richacl_masks_to_mode().

    Signed-off-by: Andreas Gruenbacher <agruen@suse.de>
    Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
    ---
    fs/richacl_base.c | 128 +++++++++++++++++++++++++++++++++++++++++++++++
    include/linux/richacl.h | 1 +
    2 files changed, 129 insertions(+), 0 deletions(-)

    diff --git a/fs/richacl_base.c b/fs/richacl_base.c
    index bfc0abf..7c77ff0 100644
    --- a/fs/richacl_base.c
    +++ b/fs/richacl_base.c
    @@ -205,3 +205,131 @@ richace_set_who(struct richace *ace, const char *who)
    return 0;
    }
    EXPORT_SYMBOL_GPL(richace_set_who);
    +
    +/**
    + * richacl_allowed_to_who - mask flags allowed to a specific who value
    + *
    + * Computes the mask values allowed to a specific who value, taking
    + * EVERYONE@ entries into account.
    + */
    +static unsigned int richacl_allowed_to_who(struct richacl *acl,
    + struct richace *who)
    +{
    + struct richace *ace;
    + unsigned int allowed = 0;
    +
    + richacl_for_each_entry_reverse(ace, acl) {
    + if (richace_is_inherit_only(ace))
    + continue;
    + if (richace_is_same_identifier(ace, who) ||
    + richace_is_everyone(ace)) {
    + if (richace_is_allow(ace))
    + allowed |= ace->e_mask;
    + else if (richace_is_deny(ace))
    + allowed &= ~ace->e_mask;
    + }
    + }
    + return allowed;
    +}
    +
    +/**
    + * richacl_group_class_allowed - maximum permissions the group class is allowed
    + *
    + * See richacl_compute_max_masks().
    + */
    +static unsigned int richacl_group_class_allowed(struct richacl *acl)
    +{
    + struct richace *ace;
    + unsigned int everyone_allowed = 0, group_class_allowed = 0;
    + int had_group_ace = 0;
    +
    + richacl_for_each_entry_reverse(ace, acl) {
    + if (richace_is_inherit_only(ace) ||
    + richace_is_owner(ace))
    + continue;
    +
    + if (richace_is_everyone(ace)) {
    + if (richace_is_allow(ace))
    + everyone_allowed |= ace->e_mask;
    + else if (richace_is_deny(ace))
    + everyone_allowed &= ~ace->e_mask;
    + } else {
    + group_class_allowed |=
    + richacl_allowed_to_who(acl, ace);
    +
    + if (richace_is_group(ace))
    + had_group_ace = 1;
    + }
    + }
    + if (!had_group_ace)
    + group_class_allowed |= everyone_allowed;
    + return group_class_allowed;
    +}
    +
    +/**
    + * richacl_compute_max_masks - compute upper bound masks
    + *
    + * Computes upper bound owner, group, and other masks so that none of
    + * the mask flags allowed by the acl are disabled (for any choice of the
    + * file owner or group membership).
    + */
    +void richacl_compute_max_masks(struct richacl *acl)
    +{
    + unsigned int gmask = ~0;
    + struct richace *ace;
    +
    + /*
    + * @gmask contains all permissions which the group class is ever
    + * allowed. We use it to avoid adding permissions to the group mask
    + * from everyone@ allow aces which the group class is always denied
    + * through other aces. For example, the following acl would otherwise
    + * result in a group mask or rw:
    + *
    + * group@:w::deny
    + * everyone@:rw::allow
    + *
    + * Avoid computing @gmask for acls which do not include any group class
    + * deny aces: in such acls, the group class is never denied any
    + * permissions from everyone@ allow aces.
    + */
    +
    +restart:
    + acl->a_owner_mask = 0;
    + acl->a_group_mask = 0;
    + acl->a_other_mask = 0;
    +
    + richacl_for_each_entry_reverse(ace, acl) {
    + if (richace_is_inherit_only(ace))
    + continue;
    +
    + if (richace_is_owner(ace)) {
    + if (richace_is_allow(ace))
    + acl->a_owner_mask |= ace->e_mask;
    + else if (richace_is_deny(ace))
    + acl->a_owner_mask &= ~ace->e_mask;
    + } else if (richace_is_everyone(ace)) {
    + if (richace_is_allow(ace)) {
    + acl->a_owner_mask |= ace->e_mask;
    + acl->a_group_mask |= ace->e_mask & gmask;
    + acl->a_other_mask |= ace->e_mask;
    + } else if (richace_is_deny(ace)) {
    + acl->a_owner_mask &= ~ace->e_mask;
    + acl->a_group_mask &= ~ace->e_mask;
    + acl->a_other_mask &= ~ace->e_mask;
    + }
    + } else {
    + if (richace_is_allow(ace)) {
    + acl->a_owner_mask |= ace->e_mask & gmask;
    + acl->a_group_mask |= ace->e_mask & gmask;
    + } else if (richace_is_deny(ace) && gmask == ~0) {
    + gmask = richacl_group_class_allowed(acl);
    + if (likely(gmask != ~0))
    + /* should always be true */
    + goto restart;
    + }
    + }
    + }
    +
    + acl->a_flags &= ~ACL4_MASKED;
    +}
    +EXPORT_SYMBOL_GPL(richacl_compute_max_masks);
    diff --git a/include/linux/richacl.h b/include/linux/richacl.h
    index 399dbc9..f491e59 100644
    --- a/include/linux/richacl.h
    +++ b/include/linux/richacl.h
    @@ -287,5 +287,6 @@ extern int richace_set_who(struct richace *, const char *);
    extern int richacl_masks_to_mode(const struct richacl *);
    extern unsigned int richacl_mode_to_mask(mode_t);
    extern unsigned int richacl_want_to_mask(int);
    +extern void richacl_compute_max_masks(struct richacl *);

    #endif /* __RICHACL_H */
    --
    1.7.0.4


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