[PATCH v13 29/51] richacl: Move everyone@ aces down the acl

Andreas Gruenbacher
2015-11-03T15:20:59Z

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 <agruenba@redhat.com>
Reviewed-by: J. Bruce Fields <bfields@redhat.com>
---
fs/richacl_compat.c | 65 +++++++++++++++++++++++++++++++++++++++++++++++++++++
1 file changed, 65 insertions(+)

diff --git a/fs/richacl_compat.c b/fs/richacl_compat.c
index 5c59999..962d314 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;
+ 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;
+}