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-rw-r--r--pkg/sentry/vfs/mount.go354
1 files changed, 317 insertions, 37 deletions
diff --git a/pkg/sentry/vfs/mount.go b/pkg/sentry/vfs/mount.go
index 1fbb420f9..32f901bd8 100644
--- a/pkg/sentry/vfs/mount.go
+++ b/pkg/sentry/vfs/mount.go
@@ -15,7 +15,11 @@
package vfs
import (
+ "bytes"
+ "fmt"
"math"
+ "sort"
+ "strings"
"sync/atomic"
"gvisor.dev/gvisor/pkg/abi/linux"
@@ -38,14 +42,23 @@ import (
//
// Mount is analogous to Linux's struct mount. (gVisor does not distinguish
// between struct mount and struct vfsmount.)
+//
+// +stateify savable
type Mount struct {
- // vfs, fs, and root are immutable. References are held on fs and root.
+ // vfs, fs, root are immutable. References are held on fs and root.
//
// Invariant: root belongs to fs.
vfs *VirtualFilesystem
fs *Filesystem
root *Dentry
+ // ID is the immutable mount ID.
+ ID uint64
+
+ // Flags contains settings as specified for mount(2), e.g. MS_NOEXEC, except
+ // for MS_RDONLY which is tracked in "writers". Immutable.
+ Flags MountFlags
+
// key is protected by VirtualFilesystem.mountMu and
// VirtualFilesystem.mounts.seq, and may be nil. References are held on
// key.parent and key.point if they are not nil.
@@ -79,13 +92,43 @@ type Mount struct {
writers int64
}
-// A MountNamespace is a collection of Mounts.
-//
+func newMount(vfs *VirtualFilesystem, fs *Filesystem, root *Dentry, mntns *MountNamespace, opts *MountOptions) *Mount {
+ mnt := &Mount{
+ ID: atomic.AddUint64(&vfs.lastMountID, 1),
+ Flags: opts.Flags,
+ vfs: vfs,
+ fs: fs,
+ root: root,
+ ns: mntns,
+ refs: 1,
+ }
+ if opts.ReadOnly {
+ mnt.setReadOnlyLocked(true)
+ }
+ return mnt
+}
+
+// Options returns a copy of the MountOptions currently applicable to mnt.
+func (mnt *Mount) Options() MountOptions {
+ mnt.vfs.mountMu.Lock()
+ defer mnt.vfs.mountMu.Unlock()
+ return MountOptions{
+ Flags: mnt.Flags,
+ ReadOnly: mnt.readOnly(),
+ }
+}
+
+// A MountNamespace is a collection of Mounts.//
// MountNamespaces are reference-counted. Unless otherwise specified, all
// MountNamespace methods require that a reference is held.
//
// MountNamespace is analogous to Linux's struct mnt_namespace.
+//
+// +stateify savable
type MountNamespace struct {
+ // Owner is the usernamespace that owns this mount namespace.
+ Owner *auth.UserNamespace
+
// root is the MountNamespace's root mount. root is immutable.
root *Mount
@@ -114,6 +157,7 @@ type MountNamespace struct {
func (vfs *VirtualFilesystem) NewMountNamespace(ctx context.Context, creds *auth.Credentials, source, fsTypeName string, opts *GetFilesystemOptions) (*MountNamespace, error) {
rft := vfs.getFilesystemType(fsTypeName)
if rft == nil {
+ ctx.Warningf("Unknown filesystem type: %s", fsTypeName)
return nil, syserror.ENODEV
}
fs, root, err := rft.fsType.GetFilesystem(ctx, vfs, creds, source, *opts)
@@ -121,49 +165,63 @@ func (vfs *VirtualFilesystem) NewMountNamespace(ctx context.Context, creds *auth
return nil, err
}
mntns := &MountNamespace{
+ Owner: creds.UserNamespace,
refs: 1,
mountpoints: make(map[*Dentry]uint32),
}
- mntns.root = &Mount{
- vfs: vfs,
- fs: fs,
- root: root,
- ns: mntns,
- refs: 1,
- }
+ mntns.root = newMount(vfs, fs, root, mntns, &MountOptions{})
return mntns, nil
}
-// MountAt creates and mounts a Filesystem configured by the given arguments.
-func (vfs *VirtualFilesystem) MountAt(ctx context.Context, creds *auth.Credentials, source string, target *PathOperation, fsTypeName string, opts *MountOptions) error {
+// NewDisconnectedMount returns a Mount representing fs with the given root
+// (which may be nil). The new Mount is not associated with any MountNamespace
+// and is not connected to any other Mounts. References are taken on fs and
+// root.
+func (vfs *VirtualFilesystem) NewDisconnectedMount(fs *Filesystem, root *Dentry, opts *MountOptions) (*Mount, error) {
+ fs.IncRef()
+ if root != nil {
+ root.IncRef()
+ }
+ return newMount(vfs, fs, root, nil /* mntns */, opts), nil
+}
+
+// MountDisconnected creates a Filesystem configured by the given arguments,
+// then returns a Mount representing it. The new Mount is not associated with
+// any MountNamespace and is not connected to any other Mounts.
+func (vfs *VirtualFilesystem) MountDisconnected(ctx context.Context, creds *auth.Credentials, source string, fsTypeName string, opts *MountOptions) (*Mount, error) {
rft := vfs.getFilesystemType(fsTypeName)
if rft == nil {
- return syserror.ENODEV
+ return nil, syserror.ENODEV
}
if !opts.InternalMount && !rft.opts.AllowUserMount {
- return syserror.ENODEV
+ return nil, syserror.ENODEV
}
fs, root, err := rft.fsType.GetFilesystem(ctx, vfs, creds, source, opts.GetFilesystemOptions)
if err != nil {
- return err
+ return nil, err
}
+ defer root.DecRef()
+ defer fs.DecRef()
+ return vfs.NewDisconnectedMount(fs, root, opts)
+}
+
+// ConnectMountAt connects mnt at the path represented by target.
+//
+// Preconditions: mnt must be disconnected.
+func (vfs *VirtualFilesystem) ConnectMountAt(ctx context.Context, creds *auth.Credentials, mnt *Mount, target *PathOperation) error {
// We can't hold vfs.mountMu while calling FilesystemImpl methods due to
// lock ordering.
vd, err := vfs.GetDentryAt(ctx, creds, target, &GetDentryOptions{})
if err != nil {
- root.DecRef()
- fs.DecRef()
return err
}
vfs.mountMu.Lock()
vd.dentry.mu.Lock()
for {
- if vd.dentry.IsDisowned() {
+ if vd.dentry.dead {
vd.dentry.mu.Unlock()
vfs.mountMu.Unlock()
vd.DecRef()
- root.DecRef()
- fs.DecRef()
return syserror.ENOENT
}
// vd might have been mounted over between vfs.GetDentryAt() and
@@ -192,17 +250,10 @@ func (vfs *VirtualFilesystem) MountAt(ctx context.Context, creds *auth.Credentia
}
vd.dentry.mu.Lock()
}
- // TODO: Linux requires that either both the mount point and the mount root
- // are directories, or neither are, and returns ENOTDIR if this is not the
- // case.
+ // TODO(gvisor.dev/issue/1035): Linux requires that either both the mount
+ // point and the mount root are directories, or neither are, and returns
+ // ENOTDIR if this is not the case.
mntns := vd.mount.ns
- mnt := &Mount{
- vfs: vfs,
- fs: fs,
- root: root,
- ns: mntns,
- refs: 1,
- }
vfs.mounts.seq.BeginWrite()
vfs.connectLocked(mnt, vd, mntns)
vfs.mounts.seq.EndWrite()
@@ -211,6 +262,19 @@ func (vfs *VirtualFilesystem) MountAt(ctx context.Context, creds *auth.Credentia
return nil
}
+// MountAt creates and mounts a Filesystem configured by the given arguments.
+func (vfs *VirtualFilesystem) MountAt(ctx context.Context, creds *auth.Credentials, source string, target *PathOperation, fsTypeName string, opts *MountOptions) error {
+ mnt, err := vfs.MountDisconnected(ctx, creds, source, fsTypeName, opts)
+ if err != nil {
+ return err
+ }
+ defer mnt.DecRef()
+ if err := vfs.ConnectMountAt(ctx, creds, mnt, target); err != nil {
+ return err
+ }
+ return nil
+}
+
// UmountAt removes the Mount at the given path.
func (vfs *VirtualFilesystem) UmountAt(ctx context.Context, creds *auth.Credentials, pop *PathOperation, opts *UmountOptions) error {
if opts.Flags&^(linux.MNT_FORCE|linux.MNT_DETACH) != 0 {
@@ -218,6 +282,9 @@ func (vfs *VirtualFilesystem) UmountAt(ctx context.Context, creds *auth.Credenti
}
// MNT_FORCE is currently unimplemented except for the permission check.
+ // Force unmounting specifically requires CAP_SYS_ADMIN in the root user
+ // namespace, and not in the owner user namespace for the target mount. See
+ // fs/namespace.c:SYSCALL_DEFINE2(umount, ...)
if opts.Flags&linux.MNT_FORCE != 0 && creds.HasCapabilityIn(linux.CAP_SYS_ADMIN, creds.UserNamespace.Root()) {
return syserror.EPERM
}
@@ -231,14 +298,17 @@ func (vfs *VirtualFilesystem) UmountAt(ctx context.Context, creds *auth.Credenti
return syserror.EINVAL
}
vfs.mountMu.Lock()
- if mntns := MountNamespaceFromContext(ctx); mntns != nil && mntns != vd.mount.ns {
- vfs.mountMu.Unlock()
- return syserror.EINVAL
+ if mntns := MountNamespaceFromContext(ctx); mntns != nil {
+ defer mntns.DecRef()
+ if mntns != vd.mount.ns {
+ vfs.mountMu.Unlock()
+ return syserror.EINVAL
+ }
}
- // TODO(jamieliu): Linux special-cases umount of the caller's root, which
- // we don't implement yet (we'll just fail it since the caller holds a
- // reference on it).
+ // TODO(gvisor.dev/issue/1035): Linux special-cases umount of the caller's
+ // root, which we don't implement yet (we'll just fail it since the caller
+ // holds a reference on it).
vfs.mounts.seq.BeginWrite()
if opts.Flags&linux.MNT_DETACH == 0 {
@@ -330,14 +400,22 @@ func (vfs *VirtualFilesystem) umountRecursiveLocked(mnt *Mount, opts *umountRecu
// references held by vd.
//
// Preconditions: vfs.mountMu must be locked. vfs.mounts.seq must be in a
-// writer critical section. d.mu must be locked. mnt.parent() == nil.
+// writer critical section. d.mu must be locked. mnt.parent() == nil, i.e. mnt
+// must not already be connected.
func (vfs *VirtualFilesystem) connectLocked(mnt *Mount, vd VirtualDentry, mntns *MountNamespace) {
+ if checkInvariants {
+ if mnt.parent() != nil {
+ panic("VFS.connectLocked called on connected mount")
+ }
+ }
+ mnt.IncRef() // dropped by callers of umountRecursiveLocked
mnt.storeKey(vd)
if vd.mount.children == nil {
vd.mount.children = make(map[*Mount]struct{})
}
vd.mount.children[mnt] = struct{}{}
atomic.AddUint32(&vd.dentry.mounts, 1)
+ mnt.ns = mntns
mntns.mountpoints[vd.dentry]++
vfs.mounts.insertSeqed(mnt)
vfsmpmounts, ok := vfs.mountpoints[vd.dentry]
@@ -355,6 +433,11 @@ func (vfs *VirtualFilesystem) connectLocked(mnt *Mount, vd VirtualDentry, mntns
// writer critical section. mnt.parent() != nil.
func (vfs *VirtualFilesystem) disconnectLocked(mnt *Mount) VirtualDentry {
vd := mnt.loadKey()
+ if checkInvariants {
+ if vd.mount != nil {
+ panic("VFS.disconnectLocked called on disconnected mount")
+ }
+ }
mnt.storeKey(VirtualDentry{})
delete(vd.mount.children, mnt)
atomic.AddUint32(&vd.dentry.mounts, math.MaxUint32) // -1
@@ -605,12 +688,34 @@ func (mnt *Mount) setReadOnlyLocked(ro bool) error {
return nil
}
+func (mnt *Mount) readOnly() bool {
+ return atomic.LoadInt64(&mnt.writers) < 0
+}
+
// Filesystem returns the mounted Filesystem. It does not take a reference on
// the returned Filesystem.
func (mnt *Mount) Filesystem() *Filesystem {
return mnt.fs
}
+// submountsLocked returns this Mount and all Mounts that are descendents of
+// it.
+//
+// Precondition: mnt.vfs.mountMu must be held.
+func (mnt *Mount) submountsLocked() []*Mount {
+ mounts := []*Mount{mnt}
+ for m := range mnt.children {
+ mounts = append(mounts, m.submountsLocked()...)
+ }
+ return mounts
+}
+
+// Root returns the mount's root. It does not take a reference on the returned
+// Dentry.
+func (mnt *Mount) Root() *Dentry {
+ return mnt.root
+}
+
// Root returns mntns' root. A reference is taken on the returned
// VirtualDentry.
func (mntns *MountNamespace) Root() VirtualDentry {
@@ -621,3 +726,178 @@ func (mntns *MountNamespace) Root() VirtualDentry {
vd.IncRef()
return vd
}
+
+// GenerateProcMounts emits the contents of /proc/[pid]/mounts for vfs to buf.
+//
+// Preconditions: taskRootDir.Ok().
+func (vfs *VirtualFilesystem) GenerateProcMounts(ctx context.Context, taskRootDir VirtualDentry, buf *bytes.Buffer) {
+ vfs.mountMu.Lock()
+ defer vfs.mountMu.Unlock()
+ rootMnt := taskRootDir.mount
+ mounts := rootMnt.submountsLocked()
+ sort.Slice(mounts, func(i, j int) bool { return mounts[i].ID < mounts[j].ID })
+ for _, mnt := range mounts {
+ // Get the path to this mount relative to task root.
+ mntRootVD := VirtualDentry{
+ mount: mnt,
+ dentry: mnt.root,
+ }
+ path, err := vfs.PathnameReachable(ctx, taskRootDir, mntRootVD)
+ if err != nil {
+ // For some reason we didn't get a path. Log a warning
+ // and run with empty path.
+ ctx.Warningf("Error getting pathname for mount root %+v: %v", mnt.root, err)
+ path = ""
+ }
+ if path == "" {
+ // Either an error occurred, or path is not reachable
+ // from root.
+ break
+ }
+
+ opts := "rw"
+ if mnt.readOnly() {
+ opts = "ro"
+ }
+ if mnt.Flags.NoATime {
+ opts = ",noatime"
+ }
+ if mnt.Flags.NoExec {
+ opts += ",noexec"
+ }
+
+ // Format:
+ // <special device or remote filesystem> <mount point> <filesystem type> <mount options> <needs dump> <fsck order>
+ //
+ // The "needs dump" and "fsck order" flags are always 0, which
+ // is allowed.
+ fmt.Fprintf(buf, "%s %s %s %s %d %d\n", "none", path, mnt.fs.FilesystemType().Name(), opts, 0, 0)
+ }
+}
+
+// GenerateProcMountInfo emits the contents of /proc/[pid]/mountinfo for vfs to
+// buf.
+//
+// Preconditions: taskRootDir.Ok().
+func (vfs *VirtualFilesystem) GenerateProcMountInfo(ctx context.Context, taskRootDir VirtualDentry, buf *bytes.Buffer) {
+ vfs.mountMu.Lock()
+ defer vfs.mountMu.Unlock()
+ rootMnt := taskRootDir.mount
+ mounts := rootMnt.submountsLocked()
+ sort.Slice(mounts, func(i, j int) bool { return mounts[i].ID < mounts[j].ID })
+ for _, mnt := range mounts {
+ // Get the path to this mount relative to task root.
+ mntRootVD := VirtualDentry{
+ mount: mnt,
+ dentry: mnt.root,
+ }
+ path, err := vfs.PathnameReachable(ctx, taskRootDir, mntRootVD)
+ if err != nil {
+ // For some reason we didn't get a path. Log a warning
+ // and run with empty path.
+ ctx.Warningf("Error getting pathname for mount root %+v: %v", mnt.root, err)
+ path = ""
+ }
+ if path == "" {
+ // Either an error occurred, or path is not reachable
+ // from root.
+ break
+ }
+ // Stat the mount root to get the major/minor device numbers.
+ pop := &PathOperation{
+ Root: mntRootVD,
+ Start: mntRootVD,
+ }
+ statx, err := vfs.StatAt(ctx, auth.NewAnonymousCredentials(), pop, &StatOptions{})
+ if err != nil {
+ // Well that's not good. Ignore this mount.
+ break
+ }
+
+ // Format:
+ // 36 35 98:0 /mnt1 /mnt2 rw,noatime master:1 - ext3 /dev/root rw,errors=continue
+ // (1)(2)(3) (4) (5) (6) (7) (8) (9) (10) (11)
+
+ // (1) Mount ID.
+ fmt.Fprintf(buf, "%d ", mnt.ID)
+
+ // (2) Parent ID (or this ID if there is no parent).
+ pID := mnt.ID
+ if p := mnt.parent(); p != nil {
+ pID = p.ID
+ }
+ fmt.Fprintf(buf, "%d ", pID)
+
+ // (3) Major:Minor device ID. We don't have a superblock, so we
+ // just use the root inode device number.
+ fmt.Fprintf(buf, "%d:%d ", statx.DevMajor, statx.DevMinor)
+
+ // (4) Root: the pathname of the directory in the filesystem
+ // which forms the root of this mount.
+ //
+ // NOTE(b/78135857): This will always be "/" until we implement
+ // bind mounts.
+ fmt.Fprintf(buf, "/ ")
+
+ // (5) Mount point (relative to process root).
+ fmt.Fprintf(buf, "%s ", manglePath(path))
+
+ // (6) Mount options.
+ opts := "rw"
+ if mnt.readOnly() {
+ opts = "ro"
+ }
+ if mnt.Flags.NoATime {
+ opts = ",noatime"
+ }
+ if mnt.Flags.NoExec {
+ opts += ",noexec"
+ }
+ fmt.Fprintf(buf, "%s ", opts)
+
+ // (7) Optional fields: zero or more fields of the form "tag[:value]".
+ // (8) Separator: the end of the optional fields is marked by a single hyphen.
+ fmt.Fprintf(buf, "- ")
+
+ // (9) Filesystem type.
+ fmt.Fprintf(buf, "%s ", mnt.fs.FilesystemType().Name())
+
+ // (10) Mount source: filesystem-specific information or "none".
+ fmt.Fprintf(buf, "none ")
+
+ // (11) Superblock options, and final newline.
+ fmt.Fprintf(buf, "%s\n", superBlockOpts(path, mnt))
+ }
+}
+
+// manglePath replaces ' ', '\t', '\n', and '\\' with their octal equivalents.
+// See Linux fs/seq_file.c:mangle_path.
+func manglePath(p string) string {
+ r := strings.NewReplacer(" ", "\\040", "\t", "\\011", "\n", "\\012", "\\", "\\134")
+ return r.Replace(p)
+}
+
+// superBlockOpts returns the super block options string for the the mount at
+// the given path.
+func superBlockOpts(mountPath string, mnt *Mount) string {
+ // gVisor doesn't (yet) have a concept of super block options, so we
+ // use the ro/rw bit from the mount flag.
+ opts := "rw"
+ if mnt.readOnly() {
+ opts = "ro"
+ }
+
+ // NOTE(b/147673608): If the mount is a cgroup, we also need to include
+ // the cgroup name in the options. For now we just read that from the
+ // path.
+ //
+ // TODO(gvisor.dev/issue/190): Once gVisor has full cgroup support, we
+ // should get this value from the cgroup itself, and not rely on the
+ // path.
+ if mnt.fs.FilesystemType().Name() == "cgroup" {
+ splitPath := strings.Split(mountPath, "/")
+ cgroupType := splitPath[len(splitPath)-1]
+ opts += "," + cgroupType
+ }
+ return opts
+}
generated by cgit v1.2.3 (git 2.39.1) at 2025-02-04 14:27:08 +0000