From 4e121b1efb52d0ccc0c89c55272b7c3da9a475f8 Mon Sep 17 00:00:00 2001 From: "Bryan C. Mills" Date: Mon, 6 Feb 2023 11:04:20 -0500 Subject: [PATCH] unix: add missing address operator in initxattrdest The purpose of the _zero variable is to provide a valid address for a pointer to an array of length zero. All other uses of the variable take its address, but one reference to it (added in CL 147850043) converts the variable (which has type uintptr) directly to an unsafe.Pointer, producing a nil pointer instead of a non-nil pointer to a zero-length array. This typo is caught by 'go vet', but was masked for a long time by the numerous false-positive warnings for the same check (#41205). For golang/go#41205. Change-Id: Ib3bebfadc6fc5574db19630169ff3f65da857bdd Reviewed-on: https://go-review.googlesource.com/c/sys/+/465597 Reviewed-by: David Chase Run-TryBot: Bryan Mills TryBot-Result: Gopher Robot Reviewed-by: Tobias Klauser Auto-Submit: Bryan Mills --- unix/xattr_bsd.go | 9 +++++++-- 1 file changed, 7 insertions(+), 2 deletions(-) diff --git a/unix/xattr_bsd.go b/unix/xattr_bsd.go index 663b3779d..f5f8e9f36 100644 --- a/unix/xattr_bsd.go +++ b/unix/xattr_bsd.go @@ -36,9 +36,14 @@ func xattrnamespace(fullattr string) (ns int, attr string, err error) { func initxattrdest(dest []byte, idx int) (d unsafe.Pointer) { if len(dest) > idx { return unsafe.Pointer(&dest[idx]) - } else { - return unsafe.Pointer(_zero) } + if dest != nil { + // extattr_get_file and extattr_list_file treat NULL differently from + // a non-NULL pointer of length zero. Preserve the property of nilness, + // even if we can't use dest directly. + return unsafe.Pointer(&_zero) + } + return nil } // FreeBSD and NetBSD implement their own syscalls to handle extended attributes