vfs: Verify acls are valid within superblock's s_user_ns.

Update posix_acl_valid to verify that an acl is within a user namespace.

Update the callers of posix_acl_valid to pass in an appropriate
user namespace.  For posix_acl_xattr_set and v9fs_xattr_set_acl pass in
inode->i_sb->s_user_ns to posix_acl_valid.  For md_unpack_acl pass in
&init_user_ns as no inode or superblock is in sight.

Acked-by: Seth Forshee <seth.forshee@canonical.com>
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>

drivers/staging/lustre/lustre/mdc/mdc_request.c

@@ -434,7 +434,7 @@ static int mdc_unpack_acl(struct ptlrpc_request *req, struct lustre_md *md)
 		return rc;
 	}
 
-	rc = posix_acl_valid(acl);
+	rc = posix_acl_valid(&init_user_ns, acl);
 	if (rc) {
 		CERROR("validate acl: %d\n", rc);
 		posix_acl_release(acl);

fs/9p/acl.c

@@ -266,7 +266,7 @@ static int v9fs_xattr_set_acl(const struct xattr_handler *handler,
 		if (IS_ERR(acl))
 			return PTR_ERR(acl);
 		else if (acl) {
-			retval = posix_acl_valid(acl);
+			retval = posix_acl_valid(inode->i_sb->s_user_ns, acl);
 			if (retval)
 				goto err_out;
 		}

fs/posix_acl.c

@@ -205,7 +205,7 @@ posix_acl_clone(const struct posix_acl *acl, gfp_t flags)
  * Check if an acl is valid. Returns 0 if it is, or -E... otherwise.
  */
 int
-posix_acl_valid(const struct posix_acl *acl)
+posix_acl_valid(struct user_namespace *user_ns, const struct posix_acl *acl)
 {
 	const struct posix_acl_entry *pa, *pe;
 	int state = ACL_USER_OBJ;
@@ -225,7 +225,7 @@ posix_acl_valid(const struct posix_acl *acl)
 			case ACL_USER:
 				if (state != ACL_USER)
 					return -EINVAL;
-				if (!uid_valid(pa->e_uid))
+				if (!kuid_has_mapping(user_ns, pa->e_uid))
 					return -EINVAL;
 				needs_mask = 1;
 				break;
@@ -240,7 +240,7 @@ posix_acl_valid(const struct posix_acl *acl)
 			case ACL_GROUP:
 				if (state != ACL_GROUP)
 					return -EINVAL;
-				if (!gid_valid(pa->e_gid))
+				if (!kgid_has_mapping(user_ns, pa->e_gid))
 					return -EINVAL;
 				needs_mask = 1;
 				break;
@@ -845,7 +845,7 @@ posix_acl_xattr_set(const struct xattr_handler *handler,
 			return PTR_ERR(acl);
 
 		if (acl) {
-			ret = posix_acl_valid(acl);
+			ret = posix_acl_valid(inode->i_sb->s_user_ns, acl);
 			if (ret)
 				goto out;
 		}

include/linux/posix_acl.h

@@ -81,7 +81,7 @@ posix_acl_release(struct posix_acl *acl)
 
 extern void posix_acl_init(struct posix_acl *, int);
 extern struct posix_acl *posix_acl_alloc(int, gfp_t);
-extern int posix_acl_valid(const struct posix_acl *);
+extern int posix_acl_valid(struct user_namespace *, const struct posix_acl *);
 extern int posix_acl_permission(struct inode *, const struct posix_acl *, int);
 extern struct posix_acl *posix_acl_from_mode(umode_t, gfp_t);
 extern int posix_acl_equiv_mode(const struct posix_acl *, umode_t *);