Support setgid directories in tmpfs and kernfs

PiperOrigin-RevId: 356868412

8 files changed, 83 insertions, 38 deletions

diff --git a/pkg/sentry/fsimpl/tmpfs/device_file.go b/pkg/sentry/fsimpl/tmpfs/device_file.go
index 9129d35b7..616ae6730 100644
--- a/pkg/sentry/fsimpl/tmpfs/device_file.go
+++ b/pkg/sentry/fsimpl/tmpfs/device_file.go
@@ -30,7 +30,7 @@ type deviceFile struct {
 	minor uint32
 }
 
-func (fs *filesystem) newDeviceFile(kuid auth.KUID, kgid auth.KGID, mode linux.FileMode, kind vfs.DeviceKind, major, minor uint32) *inode {
+func (fs *filesystem) newDeviceFile(kuid auth.KUID, kgid auth.KGID, mode linux.FileMode, kind vfs.DeviceKind, major, minor uint32, parentDir *directory) *inode {
 	file := &deviceFile{
 		kind:  kind,
 		major: major,
@@ -44,7 +44,7 @@ func (fs *filesystem) newDeviceFile(kuid auth.KUID, kgid auth.KGID, mode linux.F
 	default:
 		panic(fmt.Sprintf("invalid DeviceKind: %v", kind))
 	}
-	file.inode.init(file, fs, kuid, kgid, mode)
+	file.inode.init(file, fs, kuid, kgid, mode, parentDir)
 	file.inode.nlink = 1 // from parent directory
 	return &file.inode
 }
diff --git a/pkg/sentry/fsimpl/tmpfs/directory.go b/pkg/sentry/fsimpl/tmpfs/directory.go
index 417ac2eff..e8d256495 100644
--- a/pkg/sentry/fsimpl/tmpfs/directory.go
+++ b/pkg/sentry/fsimpl/tmpfs/directory.go
@@ -49,9 +49,9 @@ type directory struct {
 	childList dentryList
 }
 
-func (fs *filesystem) newDirectory(kuid auth.KUID, kgid auth.KGID, mode linux.FileMode) *directory {
+func (fs *filesystem) newDirectory(kuid auth.KUID, kgid auth.KGID, mode linux.FileMode, parentDir *directory) *directory {
 	dir := &directory{}
-	dir.inode.init(dir, fs, kuid, kgid, linux.S_IFDIR|mode)
+	dir.inode.init(dir, fs, kuid, kgid, linux.S_IFDIR|mode, parentDir)
 	dir.inode.nlink = 2 // from "." and parent directory or ".." for root
 	dir.dentry.inode = &dir.inode
 	dir.dentry.vfsd.Init(&dir.dentry)
diff --git a/pkg/sentry/fsimpl/tmpfs/filesystem.go b/pkg/sentry/fsimpl/tmpfs/filesystem.go
index 453e41d11..4f675c21e 100644
--- a/pkg/sentry/fsimpl/tmpfs/filesystem.go
+++ b/pkg/sentry/fsimpl/tmpfs/filesystem.go
@@ -277,7 +277,7 @@ func (fs *filesystem) MkdirAt(ctx context.Context, rp *vfs.ResolvingPath, opts v
 			return syserror.EMLINK
 		}
 		parentDir.inode.incLinksLocked() // from child's ".."
-		childDir := fs.newDirectory(creds.EffectiveKUID, creds.EffectiveKGID, opts.Mode)
+		childDir := fs.newDirectory(creds.EffectiveKUID, creds.EffectiveKGID, opts.Mode, parentDir)
 		parentDir.insertChildLocked(&childDir.dentry, name)
 		return nil
 	})
@@ -290,15 +290,15 @@ func (fs *filesystem) MknodAt(ctx context.Context, rp *vfs.ResolvingPath, opts v
 		var childInode *inode
 		switch opts.Mode.FileType() {
 		case linux.S_IFREG:
-			childInode = fs.newRegularFile(creds.EffectiveKUID, creds.EffectiveKGID, opts.Mode)
+			childInode = fs.newRegularFile(creds.EffectiveKUID, creds.EffectiveKGID, opts.Mode, parentDir)
 		case linux.S_IFIFO:
-			childInode = fs.newNamedPipe(creds.EffectiveKUID, creds.EffectiveKGID, opts.Mode)
+			childInode = fs.newNamedPipe(creds.EffectiveKUID, creds.EffectiveKGID, opts.Mode, parentDir)
 		case linux.S_IFBLK:
-			childInode = fs.newDeviceFile(creds.EffectiveKUID, creds.EffectiveKGID, opts.Mode, vfs.BlockDevice, opts.DevMajor, opts.DevMinor)
+			childInode = fs.newDeviceFile(creds.EffectiveKUID, creds.EffectiveKGID, opts.Mode, vfs.BlockDevice, opts.DevMajor, opts.DevMinor, parentDir)
 		case linux.S_IFCHR:
-			childInode = fs.newDeviceFile(creds.EffectiveKUID, creds.EffectiveKGID, opts.Mode, vfs.CharDevice, opts.DevMajor, opts.DevMinor)
+			childInode = fs.newDeviceFile(creds.EffectiveKUID, creds.EffectiveKGID, opts.Mode, vfs.CharDevice, opts.DevMajor, opts.DevMinor, parentDir)
 		case linux.S_IFSOCK:
-			childInode = fs.newSocketFile(creds.EffectiveKUID, creds.EffectiveKGID, opts.Mode, opts.Endpoint)
+			childInode = fs.newSocketFile(creds.EffectiveKUID, creds.EffectiveKGID, opts.Mode, opts.Endpoint, parentDir)
 		default:
 			return syserror.EINVAL
 		}
@@ -387,7 +387,7 @@ afterTrailingSymlink:
 		defer rp.Mount().EndWrite()
 		// Create and open the child.
 		creds := rp.Credentials()
-		child := fs.newDentry(fs.newRegularFile(creds.EffectiveKUID, creds.EffectiveKGID, opts.Mode))
+		child := fs.newDentry(fs.newRegularFile(creds.EffectiveKUID, creds.EffectiveKGID, opts.Mode, parentDir))
 		parentDir.insertChildLocked(child, name)
 		child.IncRef()
 		defer child.DecRef(ctx)
@@ -727,7 +727,7 @@ func (fs *filesystem) StatFSAt(ctx context.Context, rp *vfs.ResolvingPath) (linu
 func (fs *filesystem) SymlinkAt(ctx context.Context, rp *vfs.ResolvingPath, target string) error {
 	return fs.doCreateAt(ctx, rp, false /* dir */, func(parentDir *directory, name string) error {
 		creds := rp.Credentials()
-		child := fs.newDentry(fs.newSymlink(creds.EffectiveKUID, creds.EffectiveKGID, 0777, target))
+		child := fs.newDentry(fs.newSymlink(creds.EffectiveKUID, creds.EffectiveKGID, 0777, target, parentDir))
 		parentDir.insertChildLocked(child, name)
 		return nil
 	})
diff --git a/pkg/sentry/fsimpl/tmpfs/named_pipe.go b/pkg/sentry/fsimpl/tmpfs/named_pipe.go
index 57e7b57b0..65c2cbf86 100644
--- a/pkg/sentry/fsimpl/tmpfs/named_pipe.go
+++ b/pkg/sentry/fsimpl/tmpfs/named_pipe.go
@@ -30,9 +30,9 @@ type namedPipe struct {
 // Preconditions:
 // * fs.mu must be locked.
 // * rp.Mount().CheckBeginWrite() has been called successfully.
-func (fs *filesystem) newNamedPipe(kuid auth.KUID, kgid auth.KGID, mode linux.FileMode) *inode {
+func (fs *filesystem) newNamedPipe(kuid auth.KUID, kgid auth.KGID, mode linux.FileMode, parentDir *directory) *inode {
 	file := &namedPipe{pipe: pipe.NewVFSPipe(true /* isNamed */, pipe.DefaultPipeSize)}
-	file.inode.init(file, fs, kuid, kgid, linux.S_IFIFO|mode)
+	file.inode.init(file, fs, kuid, kgid, linux.S_IFIFO|mode, parentDir)
 	file.inode.nlink = 1 // Only the parent has a link.
 	return &file.inode
 }
diff --git a/pkg/sentry/fsimpl/tmpfs/regular_file.go b/pkg/sentry/fsimpl/tmpfs/regular_file.go
index 82a743ff3..a6d161882 100644
--- a/pkg/sentry/fsimpl/tmpfs/regular_file.go
+++ b/pkg/sentry/fsimpl/tmpfs/regular_file.go
@@ -91,13 +91,13 @@ type regularFile struct {
 	size uint64
 }
 
-func (fs *filesystem) newRegularFile(kuid auth.KUID, kgid auth.KGID, mode linux.FileMode) *inode {
+func (fs *filesystem) newRegularFile(kuid auth.KUID, kgid auth.KGID, mode linux.FileMode, parentDir *directory) *inode {
 	file := &regularFile{
 		memFile:         fs.mfp.MemoryFile(),
 		memoryUsageKind: usage.Tmpfs,
 		seals:           linux.F_SEAL_SEAL,
 	}
-	file.inode.init(file, fs, kuid, kgid, linux.S_IFREG|mode)
+	file.inode.init(file, fs, kuid, kgid, linux.S_IFREG|mode, parentDir)
 	file.inode.nlink = 1 // from parent directory
 	return &file.inode
 }
@@ -116,7 +116,7 @@ func newUnlinkedRegularFileDescription(ctx context.Context, creds *auth.Credenti
 		panic("tmpfs.newUnlinkedRegularFileDescription() called with non-tmpfs mount")
 	}
 
-	inode := fs.newRegularFile(creds.EffectiveKUID, creds.EffectiveKGID, 0777)
+	inode := fs.newRegularFile(creds.EffectiveKUID, creds.EffectiveKGID, 0777, nil /* parentDir */)
 	d := fs.newDentry(inode)
 	defer d.DecRef(ctx)
 	d.name = name
@@ -443,6 +443,13 @@ func (fd *regularFileFD) pwrite(ctx context.Context, src usermem.IOSequence, off
 	rw := getRegularFileReadWriter(f, offset)
 	n, err := src.CopyInTo(ctx, rw)
 	f.inode.touchCMtimeLocked()
+	for {
+		old := atomic.LoadUint32(&f.inode.mode)
+		new := vfs.ClearSUIDAndSGID(old)
+		if swapped := atomic.CompareAndSwapUint32(&f.inode.mode, old, new); swapped {
+			break
+		}
+	}
 	putRegularFileReadWriter(rw)
 	return n, n + offset, err
 }
diff --git a/pkg/sentry/fsimpl/tmpfs/socket_file.go b/pkg/sentry/fsimpl/tmpfs/socket_file.go
index 5699d5975..6112279b0 100644
--- a/pkg/sentry/fsimpl/tmpfs/socket_file.go
+++ b/pkg/sentry/fsimpl/tmpfs/socket_file.go
@@ -28,9 +28,9 @@ type socketFile struct {
 	ep    transport.BoundEndpoint
 }
 
-func (fs *filesystem) newSocketFile(kuid auth.KUID, kgid auth.KGID, mode linux.FileMode, ep transport.BoundEndpoint) *inode {
+func (fs *filesystem) newSocketFile(kuid auth.KUID, kgid auth.KGID, mode linux.FileMode, ep transport.BoundEndpoint, parentDir *directory) *inode {
 	file := &socketFile{ep: ep}
-	file.inode.init(file, fs, kuid, kgid, mode)
+	file.inode.init(file, fs, kuid, kgid, mode, parentDir)
 	file.inode.nlink = 1 // from parent directory
 	return &file.inode
 }
diff --git a/pkg/sentry/fsimpl/tmpfs/symlink.go b/pkg/sentry/fsimpl/tmpfs/symlink.go
index a102a2ee2..6a83296bc 100644
--- a/pkg/sentry/fsimpl/tmpfs/symlink.go
+++ b/pkg/sentry/fsimpl/tmpfs/symlink.go
@@ -25,11 +25,11 @@ type symlink struct {
 	target string // immutable
 }
 
-func (fs *filesystem) newSymlink(kuid auth.KUID, kgid auth.KGID, mode linux.FileMode, target string) *inode {
+func (fs *filesystem) newSymlink(kuid auth.KUID, kgid auth.KGID, mode linux.FileMode, target string, parentDir *directory) *inode {
 	link := &symlink{
 		target: target,
 	}
-	link.inode.init(link, fs, kuid, kgid, linux.S_IFLNK|mode)
+	link.inode.init(link, fs, kuid, kgid, linux.S_IFLNK|mode, parentDir)
 	link.inode.nlink = 1 // from parent directory
 	return &link.inode
 }
diff --git a/pkg/sentry/fsimpl/tmpfs/tmpfs.go b/pkg/sentry/fsimpl/tmpfs/tmpfs.go
index b32c54e20..a01e413e0 100644
--- a/pkg/sentry/fsimpl/tmpfs/tmpfs.go
+++ b/pkg/sentry/fsimpl/tmpfs/tmpfs.go
@@ -190,11 +190,11 @@ func (fstype FilesystemType) GetFilesystem(ctx context.Context, vfsObj *vfs.Virt
 	var root *dentry
 	switch rootFileType {
 	case linux.S_IFREG:
-		root = fs.newDentry(fs.newRegularFile(rootKUID, rootKGID, rootMode))
+		root = fs.newDentry(fs.newRegularFile(rootKUID, rootKGID, rootMode, nil /* parentDir */))
 	case linux.S_IFLNK:
-		root = fs.newDentry(fs.newSymlink(rootKUID, rootKGID, rootMode, tmpfsOpts.RootSymlinkTarget))
+		root = fs.newDentry(fs.newSymlink(rootKUID, rootKGID, rootMode, tmpfsOpts.RootSymlinkTarget, nil /* parentDir */))
 	case linux.S_IFDIR:
-		root = &fs.newDirectory(rootKUID, rootKGID, rootMode).dentry
+		root = &fs.newDirectory(rootKUID, rootKGID, rootMode, nil /* parentDir */).dentry
 	default:
 		fs.vfsfs.DecRef(ctx)
 		return nil, nil, fmt.Errorf("invalid tmpfs root file type: %#o", rootFileType)
@@ -385,10 +385,19 @@ type inode struct {
 
 const maxLinks = math.MaxUint32
 
-func (i *inode) init(impl interface{}, fs *filesystem, kuid auth.KUID, kgid auth.KGID, mode linux.FileMode) {
+func (i *inode) init(impl interface{}, fs *filesystem, kuid auth.KUID, kgid auth.KGID, mode linux.FileMode, parentDir *directory) {
 	if mode.FileType() == 0 {
 		panic("file type is required in FileMode")
 	}
+
+	// Inherit the group and setgid bit as in fs/inode.c:inode_init_owner().
+	if parentDir != nil && parentDir.inode.mode&linux.S_ISGID == linux.S_ISGID {
+		kgid = auth.KGID(parentDir.inode.gid)
+		if mode&linux.S_IFDIR == linux.S_IFDIR {
+			mode |= linux.S_ISGID
+		}
+	}
+
 	i.fs = fs
 	i.mode = uint32(mode)
 	i.uid = uint32(kuid)
@@ -519,26 +528,15 @@ func (i *inode) setStat(ctx context.Context, creds *auth.Credentials, opts *vfs.
 	if err := vfs.CheckSetStat(ctx, creds, opts, mode, auth.KUID(atomic.LoadUint32(&i.uid)), auth.KGID(atomic.LoadUint32(&i.gid))); err != nil {
 		return err
 	}
+
 	i.mu.Lock()
 	defer i.mu.Unlock()
 	var (
 		needsMtimeBump bool
 		needsCtimeBump bool
 	)
+	clearSID := false
 	mask := stat.Mask
-	if mask&linux.STATX_MODE != 0 {
-		ft := atomic.LoadUint32(&i.mode) & linux.S_IFMT
-		atomic.StoreUint32(&i.mode, ft|uint32(stat.Mode&^linux.S_IFMT))
-		needsCtimeBump = true
-	}
-	if mask&linux.STATX_UID != 0 {
-		atomic.StoreUint32(&i.uid, stat.UID)
-		needsCtimeBump = true
-	}
-	if mask&linux.STATX_GID != 0 {
-		atomic.StoreUint32(&i.gid, stat.GID)
-		needsCtimeBump = true
-	}
 	if mask&linux.STATX_SIZE != 0 {
 		switch impl := i.impl.(type) {
 		case *regularFile:
@@ -547,6 +545,7 @@ func (i *inode) setStat(ctx context.Context, creds *auth.Credentials, opts *vfs.
 				return err
 			}
 			if updated {
+				clearSID = true
 				needsMtimeBump = true
 				needsCtimeBump = true
 			}
@@ -556,6 +555,31 @@ func (i *inode) setStat(ctx context.Context, creds *auth.Credentials, opts *vfs.
 			return syserror.EINVAL
 		}
 	}
+	if mask&linux.STATX_UID != 0 {
+		atomic.StoreUint32(&i.uid, stat.UID)
+		needsCtimeBump = true
+		clearSID = true
+	}
+	if mask&linux.STATX_GID != 0 {
+		atomic.StoreUint32(&i.gid, stat.GID)
+		needsCtimeBump = true
+		clearSID = true
+	}
+	if mask&linux.STATX_MODE != 0 {
+		for {
+			old := atomic.LoadUint32(&i.mode)
+			ft := old & linux.S_IFMT
+			newMode := ft | uint32(stat.Mode & ^uint16(linux.S_IFMT))
+			if clearSID {
+				newMode = vfs.ClearSUIDAndSGID(newMode)
+			}
+			if swapped := atomic.CompareAndSwapUint32(&i.mode, old, newMode); swapped {
+				clearSID = false
+				break
+			}
+		}
+		needsCtimeBump = true
+	}
 	now := i.fs.clock.Now().Nanoseconds()
 	if mask&linux.STATX_ATIME != 0 {
 		if stat.Atime.Nsec == linux.UTIME_NOW {
@@ -584,6 +608,20 @@ func (i *inode) setStat(ctx context.Context, creds *auth.Credentials, opts *vfs.
 		// Ignore the ctime bump, since we just set it ourselves.
 		needsCtimeBump = false
 	}
+
+	// We may have to clear the SUID/SGID bits, but didn't do so as part of
+	// STATX_MODE.
+	if clearSID {
+		for {
+			old := atomic.LoadUint32(&i.mode)
+			newMode := vfs.ClearSUIDAndSGID(old)
+			if swapped := atomic.CompareAndSwapUint32(&i.mode, old, newMode); swapped {
+				break
+			}
+		}
+		needsCtimeBump = true
+	}
+
 	if needsMtimeBump {
 		atomic.StoreInt64(&i.mtime, now)
 	}