fusefrontend: allow_other: close race between mkdir and chown

Fixes the same problem as described in 72b975867a3b9bdf53fc2da62e2ba4a328d7e4ab,
except for directories instead of device nodes.

2 files changed, 22 insertions, 0 deletions

diff --git a/internal/syscallcompat/sys_darwin.go b/internal/syscallcompat/sys_darwin.go
index 367f67d..39a225f 100644
--- a/internal/syscallcompat/sys_darwin.go
+++ b/internal/syscallcompat/sys_darwin.go
@@ -187,3 +187,20 @@ func Symlinkat(oldpath string, newdirfd int, newpath string) (err error) {
 	defer syscall.Fchdir(cwd)
 	return syscall.Symlink(oldpath, newpath)
 }
+
+// Poor man's Mkdirat.
+func Mkdirat(dirfd int, path string, mode uint32) (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(dirfd)
+	if err != nil {
+		return err
+	}
+	defer syscall.Fchdir(cwd)
+	return syscall.Mkdir(path, mode)
+}
diff --git a/internal/syscallcompat/sys_linux.go b/internal/syscallcompat/sys_linux.go
index 4fe44fd..1ea56b5 100644
--- a/internal/syscallcompat/sys_linux.go
+++ b/internal/syscallcompat/sys_linux.go
@@ -109,3 +109,8 @@ func Symlinkat(oldpath string, newdirfd int, newpath string) (err error) {
 	}
 	return
 }
+
+// Mkdirat syscall.
+func Mkdirat(dirfd int, path string, mode uint32) (err error) {
+	return syscall.Mkdirat(dirfd, path, mode)
+}