2 files changed, 28 insertions, 0 deletions
diff --git a/internal/syscallcompat/sys_darwin.go b/internal/syscallcompat/sys_darwin.go
index 993c229..7defc5f 100644
--- a/internal/syscallcompat/sys_darwin.go
+++ b/internal/syscallcompat/sys_darwin.go
@@ -46,6 +46,11 @@ func Openat(dirfd int, path string, flags int, mode uint32) (fd int, err error)
 	return emulateOpenat(dirfd, path, flags, mode)
 }
 
+func OpenatUser(dirfd int, path string, flags int, mode uint32, context *fuse.Context) (fd int, err error) {
+	// FIXME: take into account context.Owner
+	return Openat(dirfd, path, flags, mode)
+}
+
 func Renameat(olddirfd int, oldpath string, newdirfd int, newpath string) (err error) {
 	return emulateRenameat(olddirfd, oldpath, newdirfd, newpath)
 }
diff --git a/internal/syscallcompat/sys_linux.go b/internal/syscallcompat/sys_linux.go
index 5c180ec..595aa1d 100644
--- a/internal/syscallcompat/sys_linux.go
+++ b/internal/syscallcompat/sys_linux.go
@@ -3,6 +3,7 @@ package syscallcompat
 
 import (
 	"fmt"
+	"runtime"
 	"sync"
 	"syscall"
 
@@ -75,6 +76,28 @@ func Openat(dirfd int, path string, flags int, mode uint32) (fd int, err error)
 	return syscall.Openat(dirfd, path, flags, mode)
 }
 
+// OpenatUser runs the Openat syscall in the context of a different user.
+func OpenatUser(dirfd int, path string, flags int, mode uint32, context *fuse.Context) (fd int, err error) {
+	if context != nil {
+		runtime.LockOSThread()
+		defer runtime.UnlockOSThread()
+
+		err = syscall.Setregid(-1, int(context.Owner.Gid))
+		if err != nil {
+			return -1, err
+		}
+		defer syscall.Setregid(-1, 0)
+
+		err = syscall.Setreuid(-1, int(context.Owner.Uid))
+		if err != nil {
+			return -1, err
+		}
+		defer syscall.Setreuid(-1, 0)
+	}
+
+	return Openat(dirfd, path, flags, mode)
+}
+
 // Renameat wraps the Renameat syscall.
 func Renameat(olddirfd int, oldpath string, newdirfd int, newpath string) (err error) {
 	return syscall.Renameat(olddirfd, oldpath, newdirfd, newpath)