os: avoid symlink races in RemoveAll on Windows

Make the openat-using version of RemoveAll use the appropriate
Windows equivalent, via new portable (but internal) functions
added for os.Root.

We could reimplement everything in terms of os.Root,
but this is a bit simpler and keeps the existing code structure.

Fixes #52745

Change-Id: I0eba0286398b351f2ee9abaa60e1675173988787
Reviewed-on: https://go-review.googlesource.com/c/go/+/661575
Reviewed-by: Alan Donovan <adonovan@google.com>
Auto-Submit: Damien Neil <dneil@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>

1 files changed, 12 insertions, 0 deletions

diff --git a/src/os/root_unix.go b/src/os/root_unix.go
index ed7a406cc7..19a84c4da0 100644
--- a/src/os/root_unix.go
+++ b/src/os/root_unix.go
@@ -219,6 +219,18 @@ func removeat(fd int, name string) error {
 	return e
 }
 
+func removefileat(fd int, name string) error {
+	return ignoringEINTR(func() error {
+		return unix.Unlinkat(fd, name, 0)
+	})
+}
+
+func removedirat(fd int, name string) error {
+	return ignoringEINTR(func() error {
+		return unix.Unlinkat(fd, name, unix.AT_REMOVEDIR)
+	})
+}
+
 func renameat(oldfd int, oldname string, newfd int, newname string) error {
 	return unix.Renameat(oldfd, oldname, newfd, newname)
 }