From 248e46f320525704da917e148a8f69d9b74671a0 Mon Sep 17 00:00:00 2001
From: Dean Deng <deandeng@google.com>
Date: Thu, 19 Mar 2020 23:29:15 -0700
Subject: [PATCH] Whitelist utimensat(2).

utimensat is used by hostfs for setting timestamps on imported fds. Previously,
this would crash the sandbox since utimensat was not allowed.

Correct the VFS2 version of hostfs to match the call in VFS1.

PiperOrigin-RevId: 301970121
---
 pkg/sentry/fsimpl/host/BUILD          |  1 +
 pkg/sentry/fsimpl/host/host.go        |  4 ++--
 pkg/sentry/fsimpl/host/util.go        |  8 +++----
 pkg/sentry/fsimpl/host/util_unsafe.go | 34 +++++++++++++++++++++++++++
 runsc/boot/filter/config.go           |  8 +++++++
 5 files changed, 49 insertions(+), 6 deletions(-)
 create mode 100644 pkg/sentry/fsimpl/host/util_unsafe.go

diff --git a/pkg/sentry/fsimpl/host/BUILD b/pkg/sentry/fsimpl/host/BUILD
index 0bb4a5c3e..82e1fb74b 100644
--- a/pkg/sentry/fsimpl/host/BUILD
+++ b/pkg/sentry/fsimpl/host/BUILD
@@ -9,6 +9,7 @@ go_library(
         "ioctl_unsafe.go",
         "tty.go",
         "util.go",
+        "util_unsafe.go",
     ],
     visibility = ["//pkg/sentry:internal"],
     deps = [
diff --git a/pkg/sentry/fsimpl/host/host.go b/pkg/sentry/fsimpl/host/host.go
index 3afb41395..1f735628f 100644
--- a/pkg/sentry/fsimpl/host/host.go
+++ b/pkg/sentry/fsimpl/host/host.go
@@ -322,11 +322,11 @@ func (i *inode) SetStat(ctx context.Context, fs *vfs.Filesystem, creds *auth.Cre
 		}
 	}
 	if m&(linux.STATX_ATIME|linux.STATX_MTIME) != 0 {
-		timestamps := []unix.Timespec{
+		ts := [2]syscall.Timespec{
 			toTimespec(s.Atime, m&linux.STATX_ATIME == 0),
 			toTimespec(s.Mtime, m&linux.STATX_MTIME == 0),
 		}
-		if err := unix.UtimesNanoAt(i.hostFD, "", timestamps, unix.AT_EMPTY_PATH); err != nil {
+		if err := setTimestamps(i.hostFD, &ts); err != nil {
 			return err
 		}
 	}
diff --git a/pkg/sentry/fsimpl/host/util.go b/pkg/sentry/fsimpl/host/util.go
index d519feef5..2bc757b1a 100644
--- a/pkg/sentry/fsimpl/host/util.go
+++ b/pkg/sentry/fsimpl/host/util.go
@@ -22,15 +22,15 @@ import (
 	"gvisor.dev/gvisor/pkg/syserror"
 )
 
-func toTimespec(ts linux.StatxTimestamp, omit bool) unix.Timespec {
+func toTimespec(ts linux.StatxTimestamp, omit bool) syscall.Timespec {
 	if omit {
-		return unix.Timespec{
+		return syscall.Timespec{
 			Sec:  0,
 			Nsec: unix.UTIME_OMIT,
 		}
 	}
-	return unix.Timespec{
-		Sec:  int64(ts.Sec),
+	return syscall.Timespec{
+		Sec:  ts.Sec,
 		Nsec: int64(ts.Nsec),
 	}
 }
diff --git a/pkg/sentry/fsimpl/host/util_unsafe.go b/pkg/sentry/fsimpl/host/util_unsafe.go
new file mode 100644
index 000000000..5136ac844
--- /dev/null
+++ b/pkg/sentry/fsimpl/host/util_unsafe.go
@@ -0,0 +1,34 @@
+// Copyright 2020 The gVisor Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package host
+
+import (
+	"syscall"
+	"unsafe"
+)
+
+func setTimestamps(fd int, ts *[2]syscall.Timespec) error {
+	_, _, errno := syscall.Syscall6(
+		syscall.SYS_UTIMENSAT,
+		uintptr(fd),
+		0, /* path */
+		uintptr(unsafe.Pointer(ts)),
+		0, /* flags */
+		0, 0)
+	if errno != 0 {
+		return errno
+	}
+	return nil
+}
diff --git a/runsc/boot/filter/config.go b/runsc/boot/filter/config.go
index f459d1973..06b9f888a 100644
--- a/runsc/boot/filter/config.go
+++ b/runsc/boot/filter/config.go
@@ -291,6 +291,14 @@ var allowedSyscalls = seccomp.SyscallRules{
 			seccomp.AllowValue(uint64(os.Getpid())),
 		},
 	},
+	syscall.SYS_UTIMENSAT: []seccomp.Rule{
+		{
+			seccomp.AllowAny{},
+			seccomp.AllowValue(0), /* null pathname */
+			seccomp.AllowAny{},
+			seccomp.AllowValue(0), /* flags */
+		},
+	},
 	syscall.SYS_WRITE: {},
 	// The only user in rawfile.NonBlockingWrite3 always passes iovcnt with
 	// values 2 or 3. Three iovec-s are passed, when the PACKET_VNET_HDR