Allocate device numbers for VFS2 filesystems.

Updates #1197, #1198, #1672

PiperOrigin-RevId: 310432006

3 files changed, 24 insertions, 2 deletions

diff --git a/pkg/sentry/fsimpl/ext/ext.go b/pkg/sentry/fsimpl/ext/ext.go
index 7176af6d1..dac6effbf 100644
--- a/pkg/sentry/fsimpl/ext/ext.go
+++ b/pkg/sentry/fsimpl/ext/ext.go
@@ -105,36 +105,50 @@ func (fsType FilesystemType) GetFilesystem(ctx context.Context, vfsObj *vfs.Virt
 	// EACCESS should be returned according to mount(2). Filesystem independent
 	// flags (like readonly) are currently not available in pkg/sentry/vfs.
 
+	devMinor, err := vfsObj.GetAnonBlockDevMinor()
+	if err != nil {
+		return nil, nil, err
+	}
+
 	dev, err := getDeviceFd(source, opts)
 	if err != nil {
 		return nil, nil, err
 	}
 
-	fs := filesystem{dev: dev, inodeCache: make(map[uint32]*inode)}
+	fs := filesystem{
+		dev:        dev,
+		inodeCache: make(map[uint32]*inode),
+		devMinor:   devMinor,
+	}
 	fs.vfsfs.Init(vfsObj, &fsType, &fs)
 	fs.sb, err = readSuperBlock(dev)
 	if err != nil {
+		fs.vfsfs.DecRef()
 		return nil, nil, err
 	}
 
 	if fs.sb.Magic() != linux.EXT_SUPER_MAGIC {
 		// mount(2) specifies that EINVAL should be returned if the superblock is
 		// invalid.
+		fs.vfsfs.DecRef()
 		return nil, nil, syserror.EINVAL
 	}
 
 	// Refuse to mount if the filesystem is incompatible.
 	if !isCompatible(fs.sb) {
+		fs.vfsfs.DecRef()
 		return nil, nil, syserror.EINVAL
 	}
 
 	fs.bgs, err = readBlockGroups(dev, fs.sb)
 	if err != nil {
+		fs.vfsfs.DecRef()
 		return nil, nil, err
 	}
 
 	rootInode, err := fs.getOrCreateInodeLocked(disklayout.RootDirInode)
 	if err != nil {
+		fs.vfsfs.DecRef()
 		return nil, nil, err
 	}
 	rootInode.incRef()
diff --git a/pkg/sentry/fsimpl/ext/filesystem.go b/pkg/sentry/fsimpl/ext/filesystem.go
index 77b644275..557963e03 100644
--- a/pkg/sentry/fsimpl/ext/filesystem.go
+++ b/pkg/sentry/fsimpl/ext/filesystem.go
@@ -64,6 +64,10 @@ type filesystem struct {
 	// bgs represents all the block group descriptors for the filesystem.
 	// Immutable after initialization.
 	bgs []disklayout.BlockGroup
+
+	// devMinor is this filesystem's device minor number. Immutable after
+	// initialization.
+	devMinor uint32
 }
 
 // Compiles only if filesystem implements vfs.FilesystemImpl.
@@ -366,7 +370,9 @@ func (fs *filesystem) StatFSAt(ctx context.Context, rp *vfs.ResolvingPath) (linu
 }
 
 // Release implements vfs.FilesystemImpl.Release.
-func (fs *filesystem) Release() {}
+func (fs *filesystem) Release() {
+	fs.vfsfs.VirtualFilesystem().PutAnonBlockDevMinor(fs.devMinor)
+}
 
 // Sync implements vfs.FilesystemImpl.Sync.
 func (fs *filesystem) Sync(ctx context.Context) error {
diff --git a/pkg/sentry/fsimpl/ext/inode.go b/pkg/sentry/fsimpl/ext/inode.go
index a98512350..485f86f4b 100644
--- a/pkg/sentry/fsimpl/ext/inode.go
+++ b/pkg/sentry/fsimpl/ext/inode.go
@@ -204,6 +204,8 @@ func (in *inode) statTo(stat *linux.Statx) {
 	stat.Atime = in.diskInode.AccessTime().StatxTimestamp()
 	stat.Ctime = in.diskInode.ChangeTime().StatxTimestamp()
 	stat.Mtime = in.diskInode.ModificationTime().StatxTimestamp()
+	stat.DevMajor = linux.UNNAMED_MAJOR
+	stat.DevMinor = in.fs.devMinor
 	// TODO(b/134676337): Set stat.Blocks which is the number of 512 byte blocks
 	// (including metadata blocks) required to represent this file.
 }