From 5a56810603ff9608c98d71cbfb8a6454da4c2261 Mon Sep 17 00:00:00 2001
From: Sebastian Lackner <sebastian@fds-team.de>
Date: Tue, 28 Nov 2017 00:54:38 +0100
Subject: [PATCH] fusefrontend: Use the Symlinkat syscall for longname handling

---
 internal/fusefrontend/fs.go          |  3 +--
 internal/syscallcompat/sys_darwin.go | 17 +++++++++++++++++
 internal/syscallcompat/sys_linux.go  | 21 +++++++++++++++++++++
 3 files changed, 39 insertions(+), 2 deletions(-)

diff --git a/internal/fusefrontend/fs.go b/internal/fusefrontend/fs.go
index bb2f192..60d43f0 100644
--- a/internal/fusefrontend/fs.go
+++ b/internal/fusefrontend/fs.go
@@ -448,8 +448,7 @@ func (fs *FS) Symlink(target string, linkName string, context *fuse.Context) (co
 			return fuse.ToStatus(err)
 		}
 		// Create "gocryptfs.longfile." symlink
-		// TODO use syscall.Symlinkat once it is available in Go
-		err = syscall.Symlink(cTarget, cPath)
+		err = syscallcompat.Symlinkat(cTarget, int(dirfd.Fd()), cName)
 		if err != nil {
 			nametransform.DeleteLongName(dirfd, cName)
 		}
diff --git a/internal/syscallcompat/sys_darwin.go b/internal/syscallcompat/sys_darwin.go
index 5504860..4068e1a 100644
--- a/internal/syscallcompat/sys_darwin.go
+++ b/internal/syscallcompat/sys_darwin.go
@@ -148,3 +148,20 @@ func Fchownat(dirfd int, path string, uid int, gid int, flags int) (err error) {
 	defer syscall.Fchdir(cwd)
 	return syscall.Lchown(path, uid, gid)
 }
+
+// Poor man's Symlinkat.
+func Symlinkat(oldpath string, newdirfd int, newpath string) (err error) {
+	chdirMutex.Lock()
+	defer chdirMutex.Unlock()
+	cwd, err := syscall.Open(".", syscall.O_RDONLY, 0)
+	if err != nil {
+		return err
+	}
+	defer syscall.Close(cwd)
+	err = syscall.Fchdir(newdirfd)
+	if err != nil {
+		return err
+	}
+	defer syscall.Fchdir(cwd)
+	return syscall.Symlink(oldpath, newpath)
+}
diff --git a/internal/syscallcompat/sys_linux.go b/internal/syscallcompat/sys_linux.go
index 8a64a81..277015e 100644
--- a/internal/syscallcompat/sys_linux.go
+++ b/internal/syscallcompat/sys_linux.go
@@ -4,6 +4,7 @@ package syscallcompat
 import (
 	"sync"
 	"syscall"
+	"unsafe"
 
 	"github.com/rfjakob/gocryptfs/internal/tlog"
 )
@@ -73,3 +74,23 @@ func Dup3(oldfd int, newfd int, flags int) (err error) {
 func Fchownat(dirfd int, path string, uid int, gid int, flags int) (err error) {
 	return syscall.Fchownat(dirfd, path, uid, gid, flags)
 }
+
+// Symlinkat syscall. Unfortunately this function is not exported directly, so
+// manually call it by using the corresponding syscall number.
+func Symlinkat(oldpath string, newdirfd int, newpath string) (err error) {
+	var _p0 *byte
+	_p0, err = syscall.BytePtrFromString(oldpath)
+	if err != nil {
+		return
+	}
+	var _p1 *byte
+	_p1, err = syscall.BytePtrFromString(newpath)
+	if err != nil {
+		return
+	}
+	_, _, e1 := syscall.Syscall(syscall.SYS_SYMLINKAT, uintptr(unsafe.Pointer(_p0)), uintptr(newdirfd), uintptr(unsafe.Pointer(_p1)))
+	if e1 != 0 {
+		err = e1
+	}
+	return
+}