1 files changed, 49 insertions, 0 deletions
diff --git a/internal/syscallcompat/asuser_linux.go b/internal/syscallcompat/asuser_linux.go
new file mode 100644
index 0000000..dac94f4
--- /dev/null
+++ b/internal/syscallcompat/asuser_linux.go
@@ -0,0 +1,49 @@
+package syscallcompat
+
+import (
+	"runtime"
+
+	"golang.org/x/sys/unix"
+
+	"github.com/hanwen/go-fuse/v2/fuse"
+)
+
+// asUser runs `f()` under the effective uid, gid, groups specified
+// in `context`.
+//
+// If `context` is nil, `f()` is executed directly without switching user id.
+func asUser(f func() (int, error), context *fuse.Context) (int, error) {
+	if context == nil {
+		return f()
+	}
+
+	runtime.LockOSThread()
+	defer runtime.UnlockOSThread()
+
+	// Since go1.16beta1 (commit d1b1145cace8b968307f9311ff611e4bb810710c ,
+	// https://go-review.googlesource.com/c/go/+/210639 )
+	// syscall.{Setgroups,Setregid,Setreuid} affects all threads, which
+	// is exactly what we not want.
+	//
+	// We now use unix.{Setgroups,Setregid,Setreuid} instead.
+
+	err := unix.Setgroups(getSupplementaryGroups(context.Pid))
+	if err != nil {
+		return -1, err
+	}
+	defer unix.Setgroups(nil)
+
+	err = unix.Setregid(-1, int(context.Owner.Gid))
+	if err != nil {
+		return -1, err
+	}
+	defer unix.Setregid(-1, 0)
+
+	err = unix.Setreuid(-1, int(context.Owner.Uid))
+	if err != nil {
+		return -1, err
+	}
+	defer unix.Setreuid(-1, 0)
+
+	return f()
+}