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Diffstat (limited to 'pkg/sentry/vfs/mount.go')
-rw-r--r--pkg/sentry/vfs/mount.go319
1 files changed, 231 insertions, 88 deletions
diff --git a/pkg/sentry/vfs/mount.go b/pkg/sentry/vfs/mount.go
index 11702f720..198fb8067 100644
--- a/pkg/sentry/vfs/mount.go
+++ b/pkg/sentry/vfs/mount.go
@@ -38,16 +38,12 @@ import (
// Mount is analogous to Linux's struct mount. (gVisor does not distinguish
// between struct mount and struct vfsmount.)
type Mount struct {
- // The lower 63 bits of refs are a reference count. The MSB of refs is set
- // if the Mount has been eagerly unmounted, as by umount(2) without the
- // MNT_DETACH flag. refs is accessed using atomic memory operations.
- refs int64
-
- // The lower 63 bits of writers is the number of calls to
- // Mount.CheckBeginWrite() that have not yet been paired with a call to
- // Mount.EndWrite(). The MSB of writers is set if MS_RDONLY is in effect.
- // writers is accessed using atomic memory operations.
- writers int64
+ // vfs, fs, and root are immutable. References are held on fs and root.
+ //
+ // Invariant: root belongs to fs.
+ vfs *VirtualFilesystem
+ fs *Filesystem
+ root *Dentry
// key is protected by VirtualFilesystem.mountMu and
// VirtualFilesystem.mounts.seq, and may be nil. References are held on
@@ -57,13 +53,29 @@ type Mount struct {
// key.parent.fs.
key mountKey
- // fs, root, and ns are immutable. References are held on fs and root (but
- // not ns).
- //
- // Invariant: root belongs to fs.
- fs *Filesystem
- root *Dentry
- ns *MountNamespace
+ // ns is the namespace in which this Mount was mounted. ns is protected by
+ // VirtualFilesystem.mountMu.
+ ns *MountNamespace
+
+ // The lower 63 bits of refs are a reference count. The MSB of refs is set
+ // if the Mount has been eagerly umounted, as by umount(2) without the
+ // MNT_DETACH flag. refs is accessed using atomic memory operations.
+ refs int64
+
+ // children is the set of all Mounts for which Mount.key.parent is this
+ // Mount. children is protected by VirtualFilesystem.mountMu.
+ children map[*Mount]struct{}
+
+ // umounted is true if VFS.umountRecursiveLocked() has been called on this
+ // Mount. VirtualFilesystem does not hold a reference on Mounts for which
+ // umounted is true. umounted is protected by VirtualFilesystem.mountMu.
+ umounted bool
+
+ // The lower 63 bits of writers is the number of calls to
+ // Mount.CheckBeginWrite() that have not yet been paired with a call to
+ // Mount.EndWrite(). The MSB of writers is set if MS_RDONLY is in effect.
+ // writers is accessed using atomic memory operations.
+ writers int64
}
// A MountNamespace is a collection of Mounts.
@@ -73,13 +85,16 @@ type Mount struct {
//
// MountNamespace is analogous to Linux's struct mnt_namespace.
type MountNamespace struct {
- refs int64 // accessed using atomic memory operations
-
// root is the MountNamespace's root mount. root is immutable.
root *Mount
- // mountpoints contains all Dentries which are mount points in this
- // namespace. mountpoints is protected by VirtualFilesystem.mountMu.
+ // refs is the reference count. refs is accessed using atomic memory
+ // operations.
+ refs int64
+
+ // mountpoints maps all Dentries which are mount points in this namespace
+ // to the number of Mounts for which they are mount points. mountpoints is
+ // protected by VirtualFilesystem.mountMu.
//
// mountpoints is used to determine if a Dentry can be moved or removed
// (which requires that the Dentry is not a mount point in the calling
@@ -89,7 +104,7 @@ type MountNamespace struct {
// MountNamespace; this is required to ensure that
// VFS.PrepareDeleteDentry() and VFS.PrepareRemoveDentry() operate
// correctly on unreferenced MountNamespaces.
- mountpoints map[*Dentry]struct{}
+ mountpoints map[*Dentry]uint32
}
// NewMountNamespace returns a new mount namespace with a root filesystem
@@ -106,9 +121,10 @@ func (vfs *VirtualFilesystem) NewMountNamespace(ctx context.Context, creds *auth
}
mntns := &MountNamespace{
refs: 1,
- mountpoints: make(map[*Dentry]struct{}),
+ mountpoints: make(map[*Dentry]uint32),
}
mntns.root = &Mount{
+ vfs: vfs,
fs: fs,
root: root,
ns: mntns,
@@ -136,8 +152,10 @@ func (vfs *VirtualFilesystem) NewMount(ctx context.Context, creds *auth.Credenti
return err
}
vfs.mountMu.Lock()
+ vd.dentry.mu.Lock()
for {
if vd.dentry.IsDisowned() {
+ vd.dentry.mu.Unlock()
vfs.mountMu.Unlock()
vd.DecRef()
root.decRef(fs)
@@ -153,36 +171,208 @@ func (vfs *VirtualFilesystem) NewMount(ctx context.Context, creds *auth.Credenti
if nextmnt == nil {
break
}
- nextmnt.incRef()
+ // It's possible that nextmnt has been umounted but not disconnected,
+ // in which case vfs no longer holds a reference on it, and the last
+ // reference may be concurrently dropped even though we're holding
+ // vfs.mountMu.
+ if !nextmnt.tryIncMountedRef() {
+ break
+ }
+ // This can't fail since we're holding vfs.mountMu.
nextmnt.root.incRef(nextmnt.fs)
+ vd.dentry.mu.Unlock()
vd.DecRef()
vd = VirtualDentry{
mount: nextmnt,
dentry: nextmnt.root,
}
+ 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.
mntns := vd.mount.ns
mnt := &Mount{
+ vfs: vfs,
fs: fs,
root: root,
ns: mntns,
refs: 1,
}
- mnt.storeKey(vd.mount, vd.dentry)
+ vfs.mounts.seq.BeginWrite()
+ vfs.connectLocked(mnt, vd, mntns)
+ vfs.mounts.seq.EndWrite()
+ vd.dentry.mu.Unlock()
+ vfs.mountMu.Unlock()
+ return nil
+}
+
+type umountRecursiveOptions struct {
+ // If eager is true, ensure that future calls to Mount.tryIncMountedRef()
+ // on umounted mounts fail.
+ //
+ // eager is analogous to Linux's UMOUNT_SYNC.
+ eager bool
+
+ // If disconnectHierarchy is true, Mounts that are umounted hierarchically
+ // should be disconnected from their parents. (Mounts whose parents are not
+ // umounted, which in most cases means the Mount passed to the initial call
+ // to umountRecursiveLocked, are unconditionally disconnected for
+ // consistency with Linux.)
+ //
+ // disconnectHierarchy is analogous to Linux's !UMOUNT_CONNECTED.
+ disconnectHierarchy bool
+}
+
+// umountRecursiveLocked marks mnt and its descendants as umounted. It does not
+// release mount or dentry references; instead, it appends VirtualDentries and
+// Mounts on which references must be dropped to vdsToDecRef and mountsToDecRef
+// respectively, and returns updated slices. (This is necessary because
+// filesystem locks possibly taken by DentryImpl.DecRef() may precede
+// vfs.mountMu in the lock order, and Mount.decRef() may lock vfs.mountMu.)
+//
+// umountRecursiveLocked is analogous to Linux's fs/namespace.c:umount_tree().
+//
+// Preconditions: vfs.mountMu must be locked. vfs.mounts.seq must be in a
+// writer critical section.
+func (vfs *VirtualFilesystem) umountRecursiveLocked(mnt *Mount, opts *umountRecursiveOptions, vdsToDecRef []VirtualDentry, mountsToDecRef []*Mount) ([]VirtualDentry, []*Mount) {
+ if !mnt.umounted {
+ mnt.umounted = true
+ mountsToDecRef = append(mountsToDecRef, mnt)
+ if parent := mnt.parent(); parent != nil && (opts.disconnectHierarchy || !parent.umounted) {
+ vdsToDecRef = append(vdsToDecRef, vfs.disconnectLocked(mnt))
+ }
+ }
+ if opts.eager {
+ for {
+ refs := atomic.LoadInt64(&mnt.refs)
+ if refs < 0 {
+ break
+ }
+ if atomic.CompareAndSwapInt64(&mnt.refs, refs, refs|math.MinInt64) {
+ break
+ }
+ }
+ }
+ for child := range mnt.children {
+ vdsToDecRef, mountsToDecRef = vfs.umountRecursiveLocked(child, opts, vdsToDecRef, mountsToDecRef)
+ }
+ return vdsToDecRef, mountsToDecRef
+}
+
+// connectLocked makes vd the mount parent/point for mnt. It consumes
+// 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.
+func (vfs *VirtualFilesystem) connectLocked(mnt *Mount, vd VirtualDentry, mntns *MountNamespace) {
+ 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)
- mntns.mountpoints[vd.dentry] = struct{}{}
+ mntns.mountpoints[vd.dentry]++
+ vfs.mounts.insertSeqed(mnt)
vfsmpmounts, ok := vfs.mountpoints[vd.dentry]
if !ok {
vfsmpmounts = make(map[*Mount]struct{})
vfs.mountpoints[vd.dentry] = vfsmpmounts
}
vfsmpmounts[mnt] = struct{}{}
- vfs.mounts.Insert(mnt)
- vfs.mountMu.Unlock()
- return nil
+}
+
+// disconnectLocked makes vd have no mount parent/point and returns its old
+// mount parent/point with a reference held.
+//
+// Preconditions: vfs.mountMu must be locked. vfs.mounts.seq must be in a
+// writer critical section. mnt.parent() != nil.
+func (vfs *VirtualFilesystem) disconnectLocked(mnt *Mount) VirtualDentry {
+ vd := mnt.loadKey()
+ mnt.storeKey(VirtualDentry{})
+ delete(vd.mount.children, mnt)
+ atomic.AddUint32(&vd.dentry.mounts, math.MaxUint32) // -1
+ mnt.ns.mountpoints[vd.dentry]--
+ if mnt.ns.mountpoints[vd.dentry] == 0 {
+ delete(mnt.ns.mountpoints, vd.dentry)
+ }
+ vfs.mounts.removeSeqed(mnt)
+ vfsmpmounts := vfs.mountpoints[vd.dentry]
+ delete(vfsmpmounts, mnt)
+ if len(vfsmpmounts) == 0 {
+ delete(vfs.mountpoints, vd.dentry)
+ }
+ return vd
+}
+
+// tryIncMountedRef increments mnt's reference count and returns true. If mnt's
+// reference count is already zero, or has been eagerly umounted,
+// tryIncMountedRef does nothing and returns false.
+//
+// tryIncMountedRef does not require that a reference is held on mnt.
+func (mnt *Mount) tryIncMountedRef() bool {
+ for {
+ refs := atomic.LoadInt64(&mnt.refs)
+ if refs <= 0 { // refs < 0 => MSB set => eagerly unmounted
+ return false
+ }
+ if atomic.CompareAndSwapInt64(&mnt.refs, refs, refs+1) {
+ return true
+ }
+ }
+}
+
+func (mnt *Mount) incRef() {
+ // In general, negative values for mnt.refs are valid because the MSB is
+ // the eager-unmount bit.
+ atomic.AddInt64(&mnt.refs, 1)
+}
+
+func (mnt *Mount) decRef() {
+ refs := atomic.AddInt64(&mnt.refs, -1)
+ if refs&^math.MinInt64 == 0 { // mask out MSB
+ var vd VirtualDentry
+ if mnt.parent() != nil {
+ mnt.vfs.mountMu.Lock()
+ mnt.vfs.mounts.seq.BeginWrite()
+ vd = mnt.vfs.disconnectLocked(mnt)
+ mnt.vfs.mounts.seq.EndWrite()
+ mnt.vfs.mountMu.Unlock()
+ }
+ mnt.root.decRef(mnt.fs)
+ mnt.fs.decRef()
+ if vd.Ok() {
+ vd.DecRef()
+ }
+ }
+}
+
+// IncRef increments mntns' reference count.
+func (mntns *MountNamespace) IncRef() {
+ if atomic.AddInt64(&mntns.refs, 1) <= 1 {
+ panic("MountNamespace.IncRef() called without holding a reference")
+ }
+}
+
+// DecRef decrements mntns' reference count.
+func (mntns *MountNamespace) DecRef(vfs *VirtualFilesystem) {
+ if refs := atomic.AddInt64(&mntns.refs, -1); refs == 0 {
+ vfs.mountMu.Lock()
+ vfs.mounts.seq.BeginWrite()
+ vdsToDecRef, mountsToDecRef := vfs.umountRecursiveLocked(mntns.root, &umountRecursiveOptions{
+ disconnectHierarchy: true,
+ }, nil, nil)
+ vfs.mounts.seq.EndWrite()
+ vfs.mountMu.Unlock()
+ for _, vd := range vdsToDecRef {
+ vd.DecRef()
+ }
+ for _, mnt := range mountsToDecRef {
+ mnt.decRef()
+ }
+ } else if refs < 0 {
+ panic("MountNamespace.DecRef() called without holding a reference")
+ }
}
// getMountAt returns the last Mount in the stack mounted at (mnt, d). It takes
@@ -231,12 +421,12 @@ retryFirst:
}
// getMountpointAt returns the mount point for the stack of Mounts including
-// mnt. It takes a reference on the returned Mount and Dentry. If no such mount
+// mnt. It takes a reference on the returned VirtualDentry. If no such mount
// point exists (i.e. mnt is a root mount), getMountpointAt returns (nil, nil).
//
// Preconditions: References are held on mnt and root. vfsroot is not (mnt,
// mnt.root).
-func (vfs *VirtualFilesystem) getMountpointAt(mnt *Mount, vfsroot VirtualDentry) (*Mount, *Dentry) {
+func (vfs *VirtualFilesystem) getMountpointAt(mnt *Mount, vfsroot VirtualDentry) VirtualDentry {
// The first mount is special-cased:
//
// - The caller must have already checked mnt against vfsroot.
@@ -246,12 +436,12 @@ func (vfs *VirtualFilesystem) getMountpointAt(mnt *Mount, vfsroot VirtualDentry)
// - We don't drop the caller's reference on mnt.
retryFirst:
epoch := vfs.mounts.seq.BeginRead()
- parent, point := mnt.loadKey()
+ parent, point := mnt.parent(), mnt.point()
if !vfs.mounts.seq.ReadOk(epoch) {
goto retryFirst
}
if parent == nil {
- return nil, nil
+ return VirtualDentry{}
}
if !parent.tryIncMountedRef() {
// Raced with umount.
@@ -263,6 +453,11 @@ retryFirst:
parent.decRef()
goto retryFirst
}
+ if !vfs.mounts.seq.ReadOk(epoch) {
+ point.decRef(parent.fs)
+ parent.decRef()
+ goto retryFirst
+ }
mnt = parent
d := point
for {
@@ -274,7 +469,7 @@ retryFirst:
}
retryNotFirst:
epoch := vfs.mounts.seq.BeginRead()
- parent, point := mnt.loadKey()
+ parent, point := mnt.parent(), mnt.point()
if !vfs.mounts.seq.ReadOk(epoch) {
goto retryNotFirst
}
@@ -301,43 +496,7 @@ retryFirst:
mnt = parent
d = point
}
- return mnt, d
-}
-
-// tryIncMountedRef increments mnt's reference count and returns true. If mnt's
-// reference count is already zero, or has been eagerly unmounted,
-// tryIncMountedRef does nothing and returns false.
-//
-// tryIncMountedRef does not require that a reference is held on mnt.
-func (mnt *Mount) tryIncMountedRef() bool {
- for {
- refs := atomic.LoadInt64(&mnt.refs)
- if refs <= 0 { // refs < 0 => MSB set => eagerly unmounted
- return false
- }
- if atomic.CompareAndSwapInt64(&mnt.refs, refs, refs+1) {
- return true
- }
- }
-}
-
-func (mnt *Mount) incRef() {
- // In general, negative values for mnt.refs are valid because the MSB is
- // the eager-unmount bit.
- atomic.AddInt64(&mnt.refs, 1)
-}
-
-func (mnt *Mount) decRef() {
- refs := atomic.AddInt64(&mnt.refs, -1)
- if refs&^math.MinInt64 == 0 { // mask out MSB
- parent, point := mnt.loadKey()
- if point != nil {
- point.decRef(parent.fs)
- parent.decRef()
- }
- mnt.root.decRef(mnt.fs)
- mnt.fs.decRef()
- }
+ return VirtualDentry{mnt, d}
}
// CheckBeginWrite increments the counter of in-progress write operations on
@@ -360,7 +519,7 @@ func (mnt *Mount) EndWrite() {
atomic.AddInt64(&mnt.writers, -1)
}
-// Preconditions: VirtualFilesystem.mountMu must be locked for writing.
+// Preconditions: VirtualFilesystem.mountMu must be locked.
func (mnt *Mount) setReadOnlyLocked(ro bool) error {
if oldRO := atomic.LoadInt64(&mnt.writers) < 0; oldRO == ro {
return nil
@@ -383,22 +542,6 @@ func (mnt *Mount) Filesystem() *Filesystem {
return mnt.fs
}
-// IncRef increments mntns' reference count.
-func (mntns *MountNamespace) IncRef() {
- if atomic.AddInt64(&mntns.refs, 1) <= 1 {
- panic("MountNamespace.IncRef() called without holding a reference")
- }
-}
-
-// DecRef decrements mntns' reference count.
-func (mntns *MountNamespace) DecRef() {
- if refs := atomic.AddInt64(&mntns.refs, 0); refs == 0 {
- // TODO: unmount mntns.root
- } else if refs < 0 {
- panic("MountNamespace.DecRef() called without holding a reference")
- }
-}
-
// Root returns mntns' root. A reference is taken on the returned
// VirtualDentry.
func (mntns *MountNamespace) Root() VirtualDentry {
generated by cgit v1.2.3 (git 2.39.1) at 2024-12-23 17:37:59 +0000