From d639c3d61bfdbd42eb809c21a15275cc75524b7e Mon Sep 17 00:00:00 2001
From: Michael Pratt <mpratt@google.com>
Date: Mon, 17 Sep 2018 12:15:35 -0700
Subject: [PATCH] Allow NULL data in mount(2)

PiperOrigin-RevId: 213315267
Change-Id: I7562bcd81fb22e90aa9c7dd9eeb94803fcb8c5af
---
 pkg/sentry/syscalls/linux/sys_mount.go | 17 ++++++++++-------
 1 file changed, 10 insertions(+), 7 deletions(-)

diff --git a/pkg/sentry/syscalls/linux/sys_mount.go b/pkg/sentry/syscalls/linux/sys_mount.go
index d70b79e4f..57cedccc1 100644
--- a/pkg/sentry/syscalls/linux/sys_mount.go
+++ b/pkg/sentry/syscalls/linux/sys_mount.go
@@ -46,13 +46,16 @@ func Mount(t *kernel.Task, args arch.SyscallArguments) (uintptr, *kernel.Syscall
 		return 0, nil, err
 	}
 
-	// In Linux, a full page is always copied in regardless of null
-	// character placement, and the address is passed to each file system.
-	// Most file systems always treat this data as a string, though, and so
-	// do all of the ones we implement.
-	data, err := t.CopyInString(dataAddr, usermem.PageSize)
-	if err != nil {
-		return 0, nil, err
+	data := ""
+	if dataAddr != 0 {
+		// In Linux, a full page is always copied in regardless of null
+		// character placement, and the address is passed to each file system.
+		// Most file systems always treat this data as a string, though, and so
+		// do all of the ones we implement.
+		data, err = t.CopyInString(dataAddr, usermem.PageSize)
+		if err != nil {
+			return 0, nil, err
+		}
 	}
 
 	// Ignore magic value that was required before Linux 2.4.