[RFC v4 21/31] richacl: Move everyone@ aces down the acl

[Andreas Gruenbacher <andreas.gruenbacher-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>]

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-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>
---
 fs/richacl_compat.c | 65 +++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 65 insertions(+)

diff --git a/fs/richacl_compat.c b/fs/richacl_compat.c
index 1c62c3c..d813789 100644
--- a/fs/richacl_compat.c
+++ b/fs/richacl_compat.c
@@ -159,3 +159,68 @@ 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;
+}
-- 
2.4.2

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