device: fix device major/minor

Current gvisor doesn't give devices a right major and minor number.

When testing golang supporting of gvisor, I run the test case below:

```
$ docker run -ti --runtime runsc golang:1.12.1 bash -c "cd /usr/local/go/src && ./run.bash "
```

And it reports some errors, one of them is:

"--- FAIL: TestDevices (0.00s)
    --- FAIL: TestDevices//dev/null_1:3 (0.00s)
        dev_linux_test.go:45: for /dev/null Major(0x0) == 0, want 1
        dev_linux_test.go:48: for /dev/null Minor(0x0) == 0, want 3
        dev_linux_test.go:51: for /dev/null Mkdev(1, 3) == 0x103, want 0x0
    --- FAIL: TestDevices//dev/zero_1:5 (0.00s)
        dev_linux_test.go:45: for /dev/zero Major(0x0) == 0, want 1
        dev_linux_test.go:48: for /dev/zero Minor(0x0) == 0, want 5
        dev_linux_test.go:51: for /dev/zero Mkdev(1, 5) == 0x105, want 0x0
    --- FAIL: TestDevices//dev/random_1:8 (0.00s)
        dev_linux_test.go:45: for /dev/random Major(0x0) == 0, want 1
        dev_linux_test.go:48: for /dev/random Minor(0x0) == 0, want 8
        dev_linux_test.go:51: for /dev/random Mkdev(1, 8) == 0x108, want 0x0
    --- FAIL: TestDevices//dev/full_1:7 (0.00s)
        dev_linux_test.go:45: for /dev/full Major(0x0) == 0, want 1
        dev_linux_test.go:48: for /dev/full Minor(0x0) == 0, want 7
        dev_linux_test.go:51: for /dev/full Mkdev(1, 7) == 0x107, want 0x0
    --- FAIL: TestDevices//dev/urandom_1:9 (0.00s)
        dev_linux_test.go:45: for /dev/urandom Major(0x0) == 0, want 1
        dev_linux_test.go:48: for /dev/urandom Minor(0x0) == 0, want 9
        dev_linux_test.go:51: for /dev/urandom Mkdev(1, 9) == 0x109, want 0x0
"

So I think we'd better assign to them correct major/minor numbers following linux spec.

Signed-off-by: Wei Zhang <zhangwei198900@gmail.com>
Change-Id: I4521ee7884b4e214fd3a261929e3b6dac537ada9
PiperOrigin-RevId: 241609021

1 files changed, 29 insertions, 5 deletions

diff --git a/pkg/sentry/fs/dev/dev.go b/pkg/sentry/fs/dev/dev.go
index e1eaa08cb..fbc750a71 100644
--- a/pkg/sentry/fs/dev/dev.go
+++ b/pkg/sentry/fs/dev/dev.go
@@ -27,6 +27,19 @@ import (
 	"gvisor.googlesource.com/gvisor/pkg/sentry/usermem"
 )
 
+// Memory device numbers are from Linux's drivers/char/mem.c
+const (
+	// Mem device major.
+	memDevMajor uint16 = 1
+
+	// Mem device minors.
+	nullDevMinor    uint32 = 3
+	zeroDevMinor    uint32 = 5
+	fullDevMinor    uint32 = 7
+	randomDevMinor  uint32 = 8
+	urandomDevMinor uint32 = 9
+)
+
 func newCharacterDevice(iops fs.InodeOperations, msrc *fs.MountSource) *fs.Inode {
 	return fs.NewInode(iops, msrc, fs.StableAttr{
 		DeviceID:  devDevice.DeviceID(),
@@ -36,6 +49,17 @@ func newCharacterDevice(iops fs.InodeOperations, msrc *fs.MountSource) *fs.Inode
 	})
 }
 
+func newMemDevice(iops fs.InodeOperations, msrc *fs.MountSource, minor uint32) *fs.Inode {
+	return fs.NewInode(iops, msrc, fs.StableAttr{
+		DeviceID:        devDevice.DeviceID(),
+		InodeID:         devDevice.NextIno(),
+		BlockSize:       usermem.PageSize,
+		Type:            fs.CharacterDevice,
+		DeviceFileMajor: memDevMajor,
+		DeviceFileMinor: minor,
+	})
+}
+
 func newDirectory(ctx context.Context, msrc *fs.MountSource) *fs.Inode {
 	iops := ramfs.NewDir(ctx, nil, fs.RootOwner, fs.FilePermsFromMode(0555))
 	return fs.NewInode(iops, msrc, fs.StableAttr{
@@ -64,17 +88,17 @@ func New(ctx context.Context, msrc *fs.MountSource, binderEnabled bool, ashmemEn
 		"stdout": newSymlink(ctx, "/proc/self/fd/1", msrc),
 		"stderr": newSymlink(ctx, "/proc/self/fd/2", msrc),
 
-		"null": newCharacterDevice(newNullDevice(ctx, fs.RootOwner, 0666), msrc),
-		"zero": newCharacterDevice(newZeroDevice(ctx, fs.RootOwner, 0666), msrc),
-		"full": newCharacterDevice(newFullDevice(ctx, fs.RootOwner, 0666), msrc),
+		"null": newMemDevice(newNullDevice(ctx, fs.RootOwner, 0666), msrc, nullDevMinor),
+		"zero": newMemDevice(newZeroDevice(ctx, fs.RootOwner, 0666), msrc, zeroDevMinor),
+		"full": newMemDevice(newFullDevice(ctx, fs.RootOwner, 0666), msrc, fullDevMinor),
 
 		// This is not as good as /dev/random in linux because go
 		// runtime uses sys_random and /dev/urandom internally.
 		// According to 'man 4 random', this will be sufficient unless
 		// application uses this to generate long-lived GPG/SSL/SSH
 		// keys.
-		"random":  newCharacterDevice(newRandomDevice(ctx, fs.RootOwner, 0444), msrc),
-		"urandom": newCharacterDevice(newRandomDevice(ctx, fs.RootOwner, 0444), msrc),
+		"random":  newMemDevice(newRandomDevice(ctx, fs.RootOwner, 0444), msrc, randomDevMinor),
+		"urandom": newMemDevice(newRandomDevice(ctx, fs.RootOwner, 0444), msrc, urandomDevMinor),
 
 		"shm": tmpfs.NewDir(ctx, nil, fs.RootOwner, fs.FilePermsFromMode(0777), msrc),