Implement /proc/[pid]/mem

This PR implements /proc/[pid]/mem for `pkg/sentry/fs` (refer to #2716) and `pkg/sentry/fsimpl`.

@majek

COPYBARA_INTEGRATE_REVIEW=https://github.com/google/gvisor/pull/4060 from lnsp:proc-pid-mem 2caf9021254646f441be618a9bb5528610e44d43
PiperOrigin-RevId: 339369629

4 files changed, 242 insertions, 0 deletions

diff --git a/pkg/sentry/fs/proc/task.go b/pkg/sentry/fs/proc/task.go
index 22d658acf..450044c9c 100644
--- a/pkg/sentry/fs/proc/task.go
+++ b/pkg/sentry/fs/proc/task.go
@@ -92,6 +92,7 @@ func (p *proc) newTaskDir(t *kernel.Task, msrc *fs.MountSource, isThreadGroup bo
 		"gid_map":       newGIDMap(t, msrc),
 		"io":            newIO(t, msrc, isThreadGroup),
 		"maps":          newMaps(t, msrc),
+		"mem":           newMem(t, msrc),
 		"mountinfo":     seqfile.NewSeqFileInode(t, &mountInfoFile{t: t}, msrc),
 		"mounts":        seqfile.NewSeqFileInode(t, &mountsFile{t: t}, msrc),
 		"net":           newNetDir(t, msrc),
@@ -399,6 +400,88 @@ func newNamespaceDir(t *kernel.Task, msrc *fs.MountSource) *fs.Inode {
 	return newProcInode(t, d, msrc, fs.SpecialDirectory, t)
 }
 
+// memData implements fs.Inode for /proc/[pid]/mem.
+//
+// +stateify savable
+type memData struct {
+	fsutil.SimpleFileInode
+
+	t *kernel.Task
+}
+
+// memDataFile implements fs.FileOperations for /proc/[pid]/mem.
+//
+// +stateify savable
+type memDataFile struct {
+	fsutil.FileGenericSeek          `state:"nosave"`
+	fsutil.FileNoIoctl              `state:"nosave"`
+	fsutil.FileNoMMap               `state:"nosave"`
+	fsutil.FileNoWrite              `state:"nosave"`
+	fsutil.FileNoSplice             `state:"nosave"`
+	fsutil.FileNoopFlush            `state:"nosave"`
+	fsutil.FileNoopFsync            `state:"nosave"`
+	fsutil.FileNoopRelease          `state:"nosave"`
+	fsutil.FileNotDirReaddir        `state:"nosave"`
+	fsutil.FileUseInodeUnstableAttr `state:"nosave"`
+	waiter.AlwaysReady              `state:"nosave"`
+
+	t *kernel.Task
+}
+
+func newMem(t *kernel.Task, msrc *fs.MountSource) *fs.Inode {
+	inode := &memData{
+		SimpleFileInode: *fsutil.NewSimpleFileInode(t, fs.RootOwner, fs.FilePermsFromMode(0400), linux.PROC_SUPER_MAGIC),
+		t:               t,
+	}
+	return newProcInode(t, inode, msrc, fs.SpecialFile, t)
+}
+
+// Truncate implements fs.InodeOperations.Truncate.
+func (m *memData) Truncate(context.Context, *fs.Inode, int64) error {
+	return nil
+}
+
+// GetFile implements fs.InodeOperations.GetFile.
+func (m *memData) GetFile(ctx context.Context, dirent *fs.Dirent, flags fs.FileFlags) (*fs.File, error) {
+	// TODO(gvisor.dev/issue/260): Add check for PTRACE_MODE_ATTACH_FSCREDS
+	// Permission to read this file is governed by PTRACE_MODE_ATTACH_FSCREDS
+	// Since we dont implement setfsuid/setfsgid we can just use PTRACE_MODE_ATTACH
+	if !kernel.ContextCanTrace(ctx, m.t, true) {
+		return nil, syserror.EACCES
+	}
+	if err := checkTaskState(m.t); err != nil {
+		return nil, err
+	}
+	// Enable random access reads
+	flags.Pread = true
+	return fs.NewFile(ctx, dirent, flags, &memDataFile{t: m.t}), nil
+}
+
+// Read implements fs.FileOperations.Read.
+func (m *memDataFile) Read(ctx context.Context, _ *fs.File, dst usermem.IOSequence, offset int64) (int64, error) {
+	if dst.NumBytes() == 0 {
+		return 0, nil
+	}
+	mm, err := getTaskMM(m.t)
+	if err != nil {
+		return 0, nil
+	}
+	defer mm.DecUsers(ctx)
+	// Buffer the read data because of MM locks
+	buf := make([]byte, dst.NumBytes())
+	n, readErr := mm.CopyIn(ctx, usermem.Addr(offset), buf, usermem.IOOpts{IgnorePermissions: true})
+	if n > 0 {
+		if _, err := dst.CopyOut(ctx, buf[:n]); err != nil {
+			return 0, syserror.EFAULT
+		}
+		return int64(n), nil
+	}
+	if readErr != nil {
+		return 0, syserror.EIO
+	}
+	return 0, nil
+}
+
 // mapsData implements seqfile.SeqSource for /proc/[pid]/maps.
 //
 // +stateify savable
diff --git a/pkg/sentry/fsimpl/proc/task.go b/pkg/sentry/fsimpl/proc/task.go
index 57cf8ce26..19011b010 100644
--- a/pkg/sentry/fsimpl/proc/task.go
+++ b/pkg/sentry/fsimpl/proc/task.go
@@ -64,6 +64,7 @@ func (fs *filesystem) newTaskInode(task *kernel.Task, pidns *kernel.PIDNamespace
 		"gid_map":   fs.newTaskOwnedInode(task, fs.NextIno(), 0644, &idMapData{task: task, gids: true}),
 		"io":        fs.newTaskOwnedInode(task, fs.NextIno(), 0400, newIO(task, isThreadGroup)),
 		"maps":      fs.newTaskOwnedInode(task, fs.NextIno(), 0444, &mapsData{task: task}),
+		"mem":       fs.newMemInode(task, fs.NextIno(), 0400),
 		"mountinfo": fs.newTaskOwnedInode(task, fs.NextIno(), 0444, &mountInfoData{task: task}),
 		"mounts":    fs.newTaskOwnedInode(task, fs.NextIno(), 0444, &mountsData{task: task}),
 		"net":       fs.newTaskNetDir(task),
diff --git a/pkg/sentry/fsimpl/proc/task_files.go b/pkg/sentry/fsimpl/proc/task_files.go
index d3f4e259b..ba71d0fde 100644
--- a/pkg/sentry/fsimpl/proc/task_files.go
+++ b/pkg/sentry/fsimpl/proc/task_files.go
@@ -31,6 +31,7 @@ import (
 	"gvisor.dev/gvisor/pkg/sentry/mm"
 	"gvisor.dev/gvisor/pkg/sentry/usage"
 	"gvisor.dev/gvisor/pkg/sentry/vfs"
+	"gvisor.dev/gvisor/pkg/sync"
 	"gvisor.dev/gvisor/pkg/syserror"
 	"gvisor.dev/gvisor/pkg/usermem"
 )
@@ -366,6 +367,162 @@ func (d *idMapData) Write(ctx context.Context, src usermem.IOSequence, offset in
 	return int64(srclen), nil
 }
 
+var _ kernfs.Inode = (*memInode)(nil)
+
+// memInode implements kernfs.Inode for /proc/[pid]/mem.
+//
+// +stateify savable
+type memInode struct {
+	kernfs.InodeAttrs
+	kernfs.InodeNoStatFS
+	kernfs.InodeNoopRefCount
+	kernfs.InodeNotDirectory
+	kernfs.InodeNotSymlink
+
+	task  *kernel.Task
+	locks vfs.FileLocks
+}
+
+func (fs *filesystem) newMemInode(task *kernel.Task, ino uint64, perm linux.FileMode) kernfs.Inode {
+	// Note: credentials are overridden by taskOwnedInode.
+	inode := &memInode{task: task}
+	inode.init(task, task.Credentials(), linux.UNNAMED_MAJOR, fs.devMinor, ino, perm)
+	return &taskOwnedInode{Inode: inode, owner: task}
+}
+
+func (f *memInode) init(ctx context.Context, creds *auth.Credentials, devMajor, devMinor uint32, ino uint64, perm linux.FileMode) {
+	if perm&^linux.PermissionsMask != 0 {
+		panic(fmt.Sprintf("Only permission mask must be set: %x", perm&linux.PermissionsMask))
+	}
+	f.InodeAttrs.Init(ctx, creds, devMajor, devMinor, ino, linux.ModeRegular|perm)
+}
+
+// Open implements kernfs.Inode.Open.
+func (f *memInode) Open(ctx context.Context, rp *vfs.ResolvingPath, d *kernfs.Dentry, opts vfs.OpenOptions) (*vfs.FileDescription, error) {
+	// TODO(gvisor.dev/issue/260): Add check for PTRACE_MODE_ATTACH_FSCREDS
+	// Permission to read this file is governed by PTRACE_MODE_ATTACH_FSCREDS
+	// Since we dont implement setfsuid/setfsgid we can just use PTRACE_MODE_ATTACH
+	if !kernel.ContextCanTrace(ctx, f.task, true) {
+		return nil, syserror.EACCES
+	}
+	if err := checkTaskState(f.task); err != nil {
+		return nil, err
+	}
+	fd := &memFD{}
+	if err := fd.Init(rp.Mount(), d, f, opts.Flags); err != nil {
+		return nil, err
+	}
+	return &fd.vfsfd, nil
+}
+
+// SetStat implements kernfs.Inode.SetStat.
+func (*memInode) SetStat(context.Context, *vfs.Filesystem, *auth.Credentials, vfs.SetStatOptions) error {
+	return syserror.EPERM
+}
+
+var _ vfs.FileDescriptionImpl = (*memFD)(nil)
+
+// memFD implements vfs.FileDescriptionImpl for /proc/[pid]/mem.
+//
+// +stateify savable
+type memFD struct {
+	vfsfd vfs.FileDescription
+	vfs.FileDescriptionDefaultImpl
+	vfs.LockFD
+
+	inode *memInode
+
+	// mu guards the fields below.
+	mu     sync.Mutex `state:"nosave"`
+	offset int64
+}
+
+// Init initializes memFD.
+func (fd *memFD) Init(m *vfs.Mount, d *kernfs.Dentry, inode *memInode, flags uint32) error {
+	fd.LockFD.Init(&inode.locks)
+	if err := fd.vfsfd.Init(fd, flags, m, d.VFSDentry(), &vfs.FileDescriptionOptions{}); err != nil {
+		return err
+	}
+	fd.inode = inode
+	return nil
+}
+
+// Seek implements vfs.FileDescriptionImpl.Seek.
+func (fd *memFD) Seek(ctx context.Context, offset int64, whence int32) (int64, error) {
+	fd.mu.Lock()
+	defer fd.mu.Unlock()
+	switch whence {
+	case linux.SEEK_SET:
+	case linux.SEEK_CUR:
+		offset += fd.offset
+	default:
+		return 0, syserror.EINVAL
+	}
+	if offset < 0 {
+		return 0, syserror.EINVAL
+	}
+	fd.offset = offset
+	return offset, nil
+}
+
+// PRead implements vfs.FileDescriptionImpl.PRead.
+func (fd *memFD) PRead(ctx context.Context, dst usermem.IOSequence, offset int64, opts vfs.ReadOptions) (int64, error) {
+	if dst.NumBytes() == 0 {
+		return 0, nil
+	}
+	m, err := getMMIncRef(fd.inode.task)
+	if err != nil {
+		return 0, nil
+	}
+	defer m.DecUsers(ctx)
+	// Buffer the read data because of MM locks
+	buf := make([]byte, dst.NumBytes())
+	n, readErr := m.CopyIn(ctx, usermem.Addr(offset), buf, usermem.IOOpts{IgnorePermissions: true})
+	if n > 0 {
+		if _, err := dst.CopyOut(ctx, buf[:n]); err != nil {
+			return 0, syserror.EFAULT
+		}
+		return int64(n), nil
+	}
+	if readErr != nil {
+		return 0, syserror.EIO
+	}
+	return 0, nil
+}
+
+// Read implements vfs.FileDescriptionImpl.Read.
+func (fd *memFD) Read(ctx context.Context, dst usermem.IOSequence, opts vfs.ReadOptions) (int64, error) {
+	fd.mu.Lock()
+	n, err := fd.PRead(ctx, dst, fd.offset, opts)
+	fd.offset += n
+	fd.mu.Unlock()
+	return n, err
+}
+
+// Stat implements vfs.FileDescriptionImpl.Stat.
+func (fd *memFD) Stat(ctx context.Context, opts vfs.StatOptions) (linux.Statx, error) {
+	fs := fd.vfsfd.VirtualDentry().Mount().Filesystem()
+	return fd.inode.Stat(ctx, fs, opts)
+}
+
+// SetStat implements vfs.FileDescriptionImpl.SetStat.
+func (fd *memFD) SetStat(context.Context, vfs.SetStatOptions) error {
+	return syserror.EPERM
+}
+
+// Release implements vfs.FileDescriptionImpl.Release.
+func (fd *memFD) Release(context.Context) {}
+
+// LockPOSIX implements vfs.FileDescriptionImpl.LockPOSIX.
+func (fd *memFD) LockPOSIX(ctx context.Context, uid fslock.UniqueID, t fslock.LockType, start, length uint64, whence int16, block fslock.Blocker) error {
+	return fd.Locks().LockPOSIX(ctx, &fd.vfsfd, uid, t, start, length, whence, block)
+}
+
+// UnlockPOSIX implements vfs.FileDescriptionImpl.UnlockPOSIX.
+func (fd *memFD) UnlockPOSIX(ctx context.Context, uid fslock.UniqueID, start, length uint64, whence int16) error {
+	return fd.Locks().UnlockPOSIX(ctx, &fd.vfsfd, uid, start, length, whence)
+}
+
 // mapsData implements vfs.DynamicBytesSource for /proc/[pid]/maps.
 //
 // +stateify savable
diff --git a/pkg/sentry/fsimpl/proc/tasks_test.go b/pkg/sentry/fsimpl/proc/tasks_test.go
index 2582ababd..7ee6227a9 100644
--- a/pkg/sentry/fsimpl/proc/tasks_test.go
+++ b/pkg/sentry/fsimpl/proc/tasks_test.go
@@ -77,6 +77,7 @@ var (
 		"gid_map":       linux.DT_REG,
 		"io":            linux.DT_REG,
 		"maps":          linux.DT_REG,
+		"mem":           linux.DT_REG,
 		"mountinfo":     linux.DT_REG,
 		"mounts":        linux.DT_REG,
 		"net":           linux.DT_DIR,