@@ -485,3 +485,57 @@ richacl_inherit(const struct richacl *dir_acl, int isdir)
return acl;
}
+
+/**
+ * richacl_equiv_mode - check if @acl is equivalent to file permission bits
+ * @mode_p: the file mode (including the file type)
+ *
+ * If @acl can be fully represented by file permission bits, this function
+ * returns 0, and the file permission bits in @mode_p are set to the equivalent
+ * of @acl.
+ *
+ * This function is used to avoid storing richacls on disk if the acl can be
+ * computed from the file permission bits. It allows user-space to make sure
+ * that a file has no explicit richacl set.
+ */
+int
+richacl_equiv_mode(const struct richacl *acl, mode_t *mode_p)
+{
+ const struct richace *ace = acl->a_entries;
+ unsigned int x;
+ mode_t mode;
+
+ if (acl->a_count != 1 ||
+ acl->a_flags != RICHACL_MASKED ||
+ !richace_is_everyone(ace) ||
+ !richace_is_allow(ace) ||
+ ace->e_flags & ~RICHACE_SPECIAL_WHO)
+ return -1;
+
+ /*
+ * Figure out the permissions we care about: RICHACE_DELETE_CHILD is
+ * meaningless for non-directories, so we ignore it.
+ */
+ x = ~RICHACE_POSIX_ALWAYS_ALLOWED;
+ if (!S_ISDIR(*mode_p))
+ x &= ~RICHACE_DELETE_CHILD;
+
+ mode = richacl_masks_to_mode(acl);
+ if ((acl->a_group_mask & x) != (richacl_mode_to_mask(mode >> 3) & x) ||
+ (acl->a_other_mask & x) != (richacl_mode_to_mask(mode) & x))
+ return -1;
+
+ /*
+ * Ignore permissions which the owner is always allowed.
+ */
+ x &= ~RICHACE_POSIX_OWNER_ALLOWED;
+ if ((acl->a_owner_mask & x) != (richacl_mode_to_mask(mode >> 6) & x))
+ return -1;
+
+ if ((ace->e_mask & x) != (RICHACE_POSIX_MODE_ALL & x))
+ return -1;
+
+ *mode_p = (*mode_p & ~S_IRWXUGO) | mode;
+ return 0;
+}
+EXPORT_SYMBOL_GPL(richacl_equiv_mode);
@@ -296,6 +296,7 @@ extern unsigned int richacl_want_to_mask(unsigned int);
extern void richacl_compute_max_masks(struct richacl *);
extern struct richacl *richacl_chmod(struct richacl *, mode_t);
extern struct richacl *richacl_inherit(const struct richacl *, int);
+extern int richacl_equiv_mode(const struct richacl *, mode_t *);
/* richacl_inode.c */
extern int richacl_permission(struct inode *, const struct richacl *, int);
This function is used to avoid storing richacls if the acl can be computed from the file permission bits. Signed-off-by: Andreas Gruenbacher <agruenba@redhat.com> --- fs/richacl_base.c | 54 +++++++++++++++++++++++++++++++++++++++++++++++++ include/linux/richacl.h | 1 + 2 files changed, 55 insertions(+)