Implement fsverity functionality

Implement calls to the fsverity kernel module, allowing containerd to
enable fsverity on blob data in the content store. This causes fsverity
to veirfy the integrity of blob data when the blob is read.

Signed-off-by: James Jenkins <James.Jenkins@ibm.com>

pkg/fsverity/fsverity_linux.go

@@ -0,0 +1,148 @@
+/*
+   Copyright The containerd 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 fsverity
+
+import (
+	"fmt"
+	"os"
+	"path/filepath"
+	"sync"
+	"syscall"
+	"unsafe"
+
+	"github.com/containerd/containerd/v2/pkg/kernelversion"
+	"golang.org/x/sys/unix"
+)
+
+type fsverityEnableArg struct {
+	version       uint32
+	hashAlgorithm uint32
+	blockSize     uint32
+	saltSize      uint32
+	saltPtr       uint64
+	sigSize       uint32
+	reserved1     uint32
+	sigPtr        uint64
+	reserved2     [11]uint64
+}
+
+const (
+	defaultBlockSize int    = 4096
+	maxDigestSize    uint16 = 64
+)
+
+var (
+	once         sync.Once
+	supported    bool
+	supportedErr error
+)
+
+func IsSupported(rootPath string) (bool, error) {
+	once.Do(func() {
+		minKernelVersion := kernelversion.KernelVersion{Kernel: 5, Major: 4}
+		s, err := kernelversion.GreaterEqualThan(minKernelVersion)
+		if err != nil {
+			supported = s
+			supportedErr = err
+			return
+		}
+
+		integrityDir := filepath.Join(rootPath, "integrity")
+		if err = os.MkdirAll(integrityDir, 0755); err != nil {
+			supported = false
+			supportedErr = err
+			return
+		}
+
+		digestPath := filepath.Join(integrityDir, "supported")
+		digestFile, err := os.Create(digestPath)
+		if err != nil {
+			supported = false
+			supportedErr = err
+			return
+		}
+
+		digestFile.Close()
+		defer os.RemoveAll(integrityDir)
+
+		eerr := Enable(digestPath)
+		if eerr != nil {
+			supported = false
+			supportedErr = eerr
+			return
+		}
+
+		supported = true
+		supportedErr = nil
+	})
+	return supported, supportedErr
+}
+
+func IsEnabled(path string) (bool, error) {
+	f, err := os.Open(path)
+	if err != nil {
+		return false, err
+	}
+
+	var attr int
+
+	_, _, flagErr := unix.Syscall(syscall.SYS_IOCTL, f.Fd(), uintptr(unix.FS_IOC_GETFLAGS), uintptr(unsafe.Pointer(&attr)))
+	if flagErr != 0 {
+		return false, fmt.Errorf("error getting inode flags: %w", flagErr)
+	}
+
+	if attr&unix.FS_VERITY_FL == unix.FS_VERITY_FL {
+		return true, nil
+	}
+
+	return false, nil
+}
+
+func Enable(path string) error {
+	f, err := os.Open(path)
+	if err != nil {
+		return err
+	}
+
+	var args = &fsverityEnableArg{}
+	args.version = 1
+	args.hashAlgorithm = 1
+
+	// fsverity block size should be the minimum between the page size
+	// and the file system block size
+	// If neither value is retrieved successfully, set fsverity block size to the default value
+	blockSize := unix.Getpagesize()
+
+	s := unix.Stat_t{}
+	serr := unix.Stat(path, &s)
+	if serr == nil && int(s.Blksize) < blockSize {
+		blockSize = int(s.Blksize)
+	}
+
+	if blockSize <= 0 {
+		blockSize = defaultBlockSize
+	}
+
+	args.blockSize = uint32(blockSize)
+
+	_, _, errno := unix.Syscall(syscall.SYS_IOCTL, f.Fd(), uintptr(unix.FS_IOC_ENABLE_VERITY), uintptr(unsafe.Pointer(args)))
+	if errno != 0 {
+		return fmt.Errorf("enable fsverity failed: %w", errno)
+	}
+
+	return nil
+}

pkg/fsverity/fsverity_other.go

@@ -0,0 +1,29 @@
+//go:build !linux
+
+/*
+   Copyright The containerd 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 fsverity
+
+import "fmt"
+
+func IsSupported(rootPath string) (bool, error) {
+	return false, fmt.Errorf("fsverity is only supported on Linux systems")
+}
+
+func Enable(_ string) error {
+	return fmt.Errorf("fsverity is only supported on Linux systems")
+}

plugins/content/local/writer.go

@@ -27,6 +27,7 @@ import (
 	"time"
 
 	"github.com/containerd/containerd/v2/core/content"
+	"github.com/containerd/containerd/v2/pkg/fsverity"
 	"github.com/containerd/errdefs"
 	"github.com/containerd/log"
 	"github.com/opencontainers/go-digest"
@@ -137,6 +138,20 @@ func (w *writer) Commit(ctx context.Context, size int64, expected digest.Digest,
 		return err
 	}
 
+	// Enable content blob integrity verification if supported
+
+	var (
+		integritySupported bool
+		supportErr         error
+	)
+	if integritySupported, supportErr = fsverity.IsSupported(w.s.root); integritySupported {
+		if err := fsverity.Enable(target); err != nil {
+			log.G(ctx).Warnf("failed to enable integrity of blob %v: %s", target, err.Error())
+		}
+	} else {
+		log.G(ctx).WithError(supportErr).Debug("fsverity integrity verification is not supported")
+	}
+
 	// Ingest has now been made available in the content store, attempt to complete
 	// setting metadata but errors should only be logged and not returned since
 	// the content store cannot be cleanly rolled back.