Gate FUSE behind a runsc flag

This change gates all FUSE commands (by gating /dev/fuse) behind a runsc
flag. In order to use FUSE commands, use the --fuse flag with the --vfs2
flag. Check if FUSE is enabled by running dmesg in the sandbox.

4 files changed, 19 insertions, 0 deletions

diff --git a/pkg/sentry/fsimpl/fuse/BUILD b/pkg/sentry/fsimpl/fuse/BUILD
index 41567967d..3e00c2abb 100644
--- a/pkg/sentry/fsimpl/fuse/BUILD
+++ b/pkg/sentry/fsimpl/fuse/BUILD
@@ -12,6 +12,7 @@ go_library(
         "//pkg/abi/linux",
         "//pkg/context",
         "//pkg/sentry/fsimpl/devtmpfs",
+        "//pkg/sentry/kernel",
         "//pkg/sentry/vfs",
         "//pkg/syserror",
         "//pkg/usermem",
diff --git a/pkg/sentry/fsimpl/fuse/dev.go b/pkg/sentry/fsimpl/fuse/dev.go
index f6a67d005..dc33268af 100644
--- a/pkg/sentry/fsimpl/fuse/dev.go
+++ b/pkg/sentry/fsimpl/fuse/dev.go
@@ -18,6 +18,7 @@ import (
 	"gvisor.dev/gvisor/pkg/abi/linux"
 	"gvisor.dev/gvisor/pkg/context"
 	"gvisor.dev/gvisor/pkg/sentry/fsimpl/devtmpfs"
+	"gvisor.dev/gvisor/pkg/sentry/kernel"
 	"gvisor.dev/gvisor/pkg/sentry/vfs"
 	"gvisor.dev/gvisor/pkg/syserror"
 	"gvisor.dev/gvisor/pkg/usermem"
@@ -30,6 +31,10 @@ type fuseDevice struct{}
 
 // Open implements vfs.Device.Open.
 func (fuseDevice) Open(ctx context.Context, mnt *vfs.Mount, vfsd *vfs.Dentry, opts vfs.OpenOptions) (*vfs.FileDescription, error) {
+	if !kernel.FUSEEnabled {
+		return nil, syserror.ENOENT
+	}
+
 	var fd DeviceFD
 	if err := fd.vfsfd.Init(&fd, opts.Flags, mnt, vfsd, &vfs.FileDescriptionOptions{
 		UseDentryMetadata: true,
diff --git a/pkg/sentry/kernel/kernel.go b/pkg/sentry/kernel/kernel.go
index 2177b785a..240cd6fe0 100644
--- a/pkg/sentry/kernel/kernel.go
+++ b/pkg/sentry/kernel/kernel.go
@@ -81,6 +81,10 @@ import (
 // easy access everywhere. To be removed once VFS2 becomes the default.
 var VFS2Enabled = false
 
+// FUSEEnabled is set to true when FUSE is enabled. Added as a global for allow
+// easy access everywhere. To be removed once FUSE is completed.
+var FUSEEnabled = false
+
 // Kernel represents an emulated Linux kernel. It must be initialized by calling
 // Init() or LoadFrom().
 //
diff --git a/pkg/sentry/kernel/syslog.go b/pkg/sentry/kernel/syslog.go
index 4607cde2f..a83ce219c 100644
--- a/pkg/sentry/kernel/syslog.go
+++ b/pkg/sentry/kernel/syslog.go
@@ -98,6 +98,15 @@ func (s *syslog) Log() []byte {
 		s.msg = append(s.msg, []byte(fmt.Sprintf(format, time, selectMessage()))...)
 	}
 
+	if VFS2Enabled {
+		time += rand.Float64() / 2
+		s.msg = append(s.msg, []byte(fmt.Sprintf(format, time, "Setting up VFS2..."))...)
+		if FUSEEnabled {
+			time += rand.Float64() / 2
+			s.msg = append(s.msg, []byte(fmt.Sprintf(format, time, "Setting up FUSE..."))...)
+		}
+	}
+
 	time += rand.Float64() / 2
 	s.msg = append(s.msg, []byte(fmt.Sprintf(format, time, "Ready!"))...)