security: Fix hook iteration and default value for inode_copy_up_xattr

inode_copy_up_xattr returns 0 to indicate the acceptance of the xattr
and 1 to reject it. If the LSM does not know about the xattr, it's
expected to return -EOPNOTSUPP, which is the correct default value for
this hook. BPF LSM, currently, uses 0 as the default value and thereby
falsely allows all overlay fs xattributes to be copied up.

The iteration logic is also updated from the "bail-on-fail"
call_int_hook to continue on the non-decisive -EOPNOTSUPP and bail out
on other values.

Fixes: 98e828a0650f ("security: Refactor declaration of LSM hooks")
Signed-off-by: KP Singh <kpsingh@google.com>
Signed-off-by: James Morris <jmorris@namei.org>

1 files changed, 16 insertions, 1 deletions

diff --git a/security/security.c b/security/security.c
index 0ce3e73edd42..70a7ad357bc6 100644
--- a/security/security.c
+++ b/security/security.c
@@ -1414,7 +1414,22 @@ EXPORT_SYMBOL(security_inode_copy_up);
 
 int security_inode_copy_up_xattr(const char *name)
 {
-	return call_int_hook(inode_copy_up_xattr, -EOPNOTSUPP, name);
+	struct security_hook_list *hp;
+	int rc;
+
+	/*
+	 * The implementation can return 0 (accept the xattr), 1 (discard the
+	 * xattr), -EOPNOTSUPP if it does not know anything about the xattr or
+	 * any other error code incase of an error.
+	 */
+	hlist_for_each_entry(hp,
+		&security_hook_heads.inode_copy_up_xattr, list) {
+		rc = hp->hook.inode_copy_up_xattr(name);
+		if (rc != LSM_RET_DEFAULT(inode_copy_up_xattr))
+			return rc;
+	}
+
+	return LSM_RET_DEFAULT(inode_copy_up_xattr);
 }
 EXPORT_SYMBOL(security_inode_copy_up_xattr);