all: fix race when allocating buffer for some windows syscalls

Fixes #9753

Change-Id: I6c641ed7ef4f687a108e7d937ab4b9c24d5baf5d
Reviewed-on: https://go-review.googlesource.com/4940
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

1 files changed, 12 insertions, 15 deletions

diff --git a/src/path/filepath/symlink_windows.go b/src/path/filepath/symlink_windows.go
index 327c2c89a3..4b38f6fac3 100644
--- a/src/path/filepath/symlink_windows.go
+++ b/src/path/filepath/symlink_windows.go
@@ -14,18 +14,17 @@ func toShort(path string) (string, error) {
 		return "", err
 	}
 	b := p // GetShortPathName says we can reuse buffer
-	n, err := syscall.GetShortPathName(&p[0], &b[0], uint32(len(b)))
-	if err != nil {
-		return "", err
-	}
-	if n > uint32(len(b)) {
-		b = make([]uint16, n)
+	n := uint32(len(b))
+	for {
 		n, err = syscall.GetShortPathName(&p[0], &b[0], uint32(len(b)))
 		if err != nil {
 			return "", err
 		}
+		if n <= uint32(len(b)) {
+			return syscall.UTF16ToString(b[:n]), nil
+		}
+		b = make([]uint16, n)
 	}
-	return syscall.UTF16ToString(b), nil
 }
 
 func toLong(path string) (string, error) {
@@ -34,19 +33,17 @@ func toLong(path string) (string, error) {
 		return "", err
 	}
 	b := p // GetLongPathName says we can reuse buffer
-	n, err := syscall.GetLongPathName(&p[0], &b[0], uint32(len(b)))
-	if err != nil {
-		return "", err
-	}
-	if n > uint32(len(b)) {
-		b = make([]uint16, n)
+	n := uint32(len(b))
+	for {
 		n, err = syscall.GetLongPathName(&p[0], &b[0], uint32(len(b)))
 		if err != nil {
 			return "", err
 		}
+		if n <= uint32(len(b)) {
+			return syscall.UTF16ToString(b[:n]), nil
+		}
+		b = make([]uint16, n)
 	}
-	b = b[:n]
-	return syscall.UTF16ToString(b), nil
 }
 
 func evalSymlinks(path string) (string, error) {