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overlayfs: implement POSIX ACLs #13909

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5 changes: 5 additions & 0 deletions pkg/sentry/fsimpl/overlay/BUILD
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Original file line number Diff line number Diff line change
Expand Up @@ -114,10 +114,15 @@ go_library(
"req_file_fd_mutex.go",
"save_restore.go",
],
imports = [
"gvisor.dev/gvisor/pkg/sentry/checkpoint",
"gvisor.dev/gvisor/pkg/sentry/vfs",
],
visibility = ["//pkg/sentry:internal"],
deps = [
"//pkg/abi/linux",
"//pkg/atomicbitops",
"//pkg/cleanup",
"//pkg/context",
"//pkg/errors/linuxerr",
"//pkg/fspath",
Expand Down
41 changes: 40 additions & 1 deletion pkg/sentry/fsimpl/overlay/copy_up.go
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Original file line number Diff line number Diff line change
Expand Up @@ -181,6 +181,13 @@ func (d *dentry) copyUpMaybeSyntheticMountpointLocked(ctx context.Context, forSy
cleanupUndoCopyUp()
return err
}
acl, newMode, err := newFD.SetPosixACL(ctx, vfs.AccessACL, d.accessACL.Load(), false /* clearSGID */)
if err != nil {
cleanupUndoCopyUp()
return err
}
d.accessACL.Store(acl)
d.mode.Store(uint32(newMode))
d.upperVD = newFD.VirtualDentry()
d.upperVD.IncRef()

Expand All @@ -207,6 +214,19 @@ func (d *dentry) copyUpMaybeSyntheticMountpointLocked(ctx context.Context, forSy
cleanupUndoCopyUp()
return err
}
acl, newMode, err := vfsObj.SetPosixACLAt(ctx, d.fs.creds, &newpop, vfs.AccessACL, d.accessACL.Load(), false /* clearSGID */)
if err != nil {
cleanupUndoCopyUp()
return err
}
d.accessACL.Store(acl)
d.mode.Store(uint32(newMode))
defaultACL, _, err := vfsObj.SetPosixACLAt(ctx, d.fs.creds, &newpop, vfs.DefaultACL, d.defaultACL.Load(), false /* clearSGID */)
if err != nil {
cleanupUndoCopyUp()
return err
}
d.defaultACL.Store(defaultACL)
upperVD, err := vfsObj.GetDentryAt(ctx, d.fs.creds, &newpop, &vfs.GetDentryOptions{})
if err != nil {
cleanupUndoCopyUp()
Expand Down Expand Up @@ -236,6 +256,13 @@ func (d *dentry) copyUpMaybeSyntheticMountpointLocked(ctx context.Context, forSy
cleanupUndoCopyUp()
return err
}
acl, newMode, err := vfsObj.SetPosixACLAt(ctx, d.fs.creds, &newpop, vfs.AccessACL, d.accessACL.Load(), false /* clearSGID */)
if err != nil {
cleanupUndoCopyUp()
return err
}
d.accessACL.Store(acl)
d.mode.Store(uint32(newMode))
upperVD, err := vfsObj.GetDentryAt(ctx, d.fs.creds, &newpop, &vfs.GetDentryOptions{})
if err != nil {
cleanupUndoCopyUp()
Expand Down Expand Up @@ -265,6 +292,13 @@ func (d *dentry) copyUpMaybeSyntheticMountpointLocked(ctx context.Context, forSy
cleanupUndoCopyUp()
return err
}
acl, newMode, err := vfsObj.SetPosixACLAt(ctx, d.fs.creds, &newpop, vfs.AccessACL, d.accessACL.Load(), false /* clearSGID */)
if err != nil {
cleanupUndoCopyUp()
return err
}
d.accessACL.Store(acl)
d.mode.Store(uint32(newMode))
upperVD, err := vfsObj.GetDentryAt(ctx, d.fs.creds, &newpop, &vfs.GetDentryOptions{})
if err != nil {
cleanupUndoCopyUp()
Expand Down Expand Up @@ -375,7 +409,7 @@ func (d *dentry) copyUpMaybeSyntheticMountpointLocked(ctx context.Context, forSy
// abort the copy-up. Loosely analogous to Linux's
// fs/overlayfs/util.c:ovl_must_copy_xattr(). Here are the differences:
// - Linux includes "system.posix_acl_access" and "system.posix_acl_default".
// As of writing, these are not supported in gVisor and so are excluded.
// In gVisor, we handle these separately.
// - Linux includes all "security.*" xattrs. gVisor only supports
// "security.capability" and so only that is included here.
func mustCopyXattr(name string) bool {
Expand Down Expand Up @@ -407,6 +441,11 @@ func (d *dentry) copyXattrsLocked(ctx context.Context) error {
continue
}

// Skip POSIX ACLs, which are handled separately.
if name == linux.XATTR_NAME_POSIX_ACL_ACCESS || name == linux.XATTR_NAME_POSIX_ACL_DEFAULT {
continue
}

value, err := vfsObj.GetXattrAt(ctx, d.fs.creds, lowerPop, &vfs.GetXattrOptions{Name: name, Size: 0})
if err != nil {
ctx.Infof("failed to copy up %q xattr because GetXattrAt failed: %v", name, err)
Expand Down
105 changes: 94 additions & 11 deletions pkg/sentry/fsimpl/overlay/filesystem.go
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Original file line number Diff line number Diff line change
Expand Up @@ -226,16 +226,27 @@ func (fs *filesystem) lookupLocked(ctx context.Context, parent *dentry, name str
// the topmost layer on which the file exists.
mask |= linux.STATX_MODE | linux.STATX_UID | linux.STATX_GID | linux.STATX_INO
}
stat, err := vfsObj.StatAt(ctx, fs.creds, &vfs.PathOperation{
childPop := &vfs.PathOperation{
Root: childVD,
Start: childVD,
}, &vfs.StatOptions{
}
stat, err := vfsObj.StatAt(ctx, fs.creds, childPop, &vfs.StatOptions{
Mask: mask,
})
if err != nil {
lookupErr = err
return false
}
acl, err := vfsObj.GetPosixACLAt(ctx, fs.creds, childPop, vfs.AccessACL)
if err != nil {
lookupErr = err
return false
}
defaultACL, err := vfsObj.GetPosixACLAt(ctx, fs.creds, childPop, vfs.DefaultACL)
if err != nil {
lookupErr = err
return false
}
if stat.Mask&mask != mask {
lookupErr = linuxerr.EREMOTE
return false
Expand Down Expand Up @@ -274,6 +285,8 @@ func (fs *filesystem) lookupLocked(ctx context.Context, parent *dentry, name str
topLookupLayer = lookupLayerLower
}
child.mode = atomicbitops.FromUint32(uint32(stat.Mode))
child.accessACL.Store(acl)
child.defaultACL.Store(defaultACL)
child.uid = atomicbitops.FromUint32(stat.UID)
child.gid = atomicbitops.FromUint32(stat.GID)
child.devMajor = atomicbitops.FromUint32(stat.DevMajor)
Expand Down Expand Up @@ -1500,7 +1513,7 @@ func (fs *filesystem) SetStatAt(ctx context.Context, rp *vfs.ResolvingPath, opts
// Precondition: d.fs.renameMu must be held for reading.
func (d *dentry) setStatLocked(ctx context.Context, rp *vfs.ResolvingPath, opts vfs.SetStatOptions) error {
mode := linux.FileMode(d.mode.Load())
if err := vfs.CheckSetStat(ctx, rp.Credentials(), &opts, mode, nil, auth.KUID(d.uid.Load()), auth.KGID(d.gid.Load())); err != nil {
if err := vfs.CheckSetStat(ctx, rp.Credentials(), &opts, mode, d.accessACL.Load(), auth.KUID(d.uid.Load()), auth.KGID(d.gid.Load())); err != nil {
return err
}
mnt := rp.Mount()
Expand Down Expand Up @@ -1758,6 +1771,13 @@ func (fs *filesystem) GetXattrAt(ctx context.Context, rp *vfs.ResolvingPath, opt
}

func (fs *filesystem) getXattr(ctx context.Context, d *dentry, creds *auth.Credentials, opts *vfs.GetXattrOptions) (string, error) {
// Handle POSIX access ACL xattr
if strings.HasPrefix(opts.Name, linux.XATTR_SYSTEM_PREFIX) {
// Handle POSIX ACL xattrs
xattr, err := vfs.ACLGetXattr(creds, opts, linux.FileMode(d.mode.Load()), d.accessACL.Load(), d.defaultACL.Load())
return xattr, err
}

if err := d.checkXattrPermissions(creds, opts.Name, vfs.MayRead); err != nil {
return "", err
}
Expand Down Expand Up @@ -1794,8 +1814,20 @@ func (fs *filesystem) SetXattrAt(ctx context.Context, rp *vfs.ResolvingPath, opt
return nil
}

// Precondition: fs.renameMu must be locked.
// Precondition: fs.renameMu must be locked, d.copyMu must be unlocked.
func (fs *filesystem) setXattrLocked(ctx context.Context, d *dentry, mnt *vfs.Mount, creds *auth.Credentials, opts *vfs.SetXattrOptions) error {
// Handle POSIX ACLs separately
if strings.HasPrefix(opts.Name, linux.XATTR_SYSTEM_PREFIX) {
acl, aclType, err := vfs.ACLSetXattr(creds, opts, linux.FileMode(d.mode.Load()), auth.KUID(d.uid.Load()))
if err != nil {
return err
}

// Set the appropriate POSIX ACL
_, _, err = fs.setPosixACLLocked(ctx, d, creds, mnt, aclType, acl, true /* clearSGID */)
return err
}

if err := d.checkXattrPermissions(creds, opts.Name, vfs.MayWrite); err != nil {
return err
}
Expand Down Expand Up @@ -1838,8 +1870,19 @@ func (fs *filesystem) RemoveXattrAt(ctx context.Context, rp *vfs.ResolvingPath,
return nil
}

// Precondition: fs.renameMu must be locked.
// Precondition: fs.renameMu must be locked, d.copyMu must be unlocked.
func (fs *filesystem) removeXattrLocked(ctx context.Context, d *dentry, mnt *vfs.Mount, creds *auth.Credentials, name string) error {
if strings.HasPrefix(name, linux.XATTR_SYSTEM_PREFIX) {
aclType, err := vfs.ACLRemoveXattr(creds, name, linux.FileMode(d.mode.Load()), auth.KUID(d.uid.Load()))
if err != nil {
return err
}

// Clear the appropriate POSIX ACL
_, _, err = fs.setPosixACLLocked(ctx, d, creds, mnt, aclType, nil, true /* clearSGID */)
return err
}

if err := d.checkXattrPermissions(creds, name, vfs.MayWrite); err != nil {
return err
}
Expand Down Expand Up @@ -1867,22 +1910,62 @@ func (fs *filesystem) GetPosixACLAt(ctx context.Context, rp *vfs.ResolvingPath,
var ds *[]*dentry
fs.renameMu.RLock()
defer fs.renameMuRUnlockAndCheckDrop(ctx, &ds)
// overlayfs does not currently support POSIX ACLs.
_, err := fs.resolveLocked(ctx, rp, &ds)
return nil, err
d, err := fs.resolveLocked(ctx, rp, &ds)
if err != nil {
return nil, err
}
switch t {
case vfs.AccessACL:
return d.accessACL.Load(), nil
case vfs.DefaultACL:
return d.defaultACL.Load(), nil
}
return nil, linuxerr.EINVAL
}

// SetPosixACLAt implements vfs.FilesystemImpl.SetPosixACLAt.
func (fs *filesystem) SetPosixACLAt(ctx context.Context, rp *vfs.ResolvingPath, t vfs.ACLType, acl *vfs.PosixACL, clearSGID bool) (*vfs.PosixACL, linux.FileMode, error) {
var ds *[]*dentry
fs.renameMu.RLock()
defer fs.renameMuRUnlockAndCheckDrop(ctx, &ds)
_, err := fs.resolveLocked(ctx, rp, &ds)
d, err := fs.resolveLocked(ctx, rp, &ds)
if err != nil {
return nil, 0, err
}
newACL, mode, err := fs.setPosixACLLocked(ctx, d, rp.Credentials(), rp.Mount(), t, acl, clearSGID)
return newACL, mode, err
}

// Precondition: fs.renameMu must be locked, d.copyMu must be unlocked.
func (fs *filesystem) setPosixACLLocked(ctx context.Context, d *dentry, creds *auth.Credentials, mnt *vfs.Mount, t vfs.ACLType, acl *vfs.PosixACL, clearSGID bool) (*vfs.PosixACL, linux.FileMode, error) {
if err := mnt.CheckBeginWrite(); err != nil {
return nil, 0, err
}
defer mnt.EndWrite()
if err := d.copyUpLocked(ctx); err != nil {
return nil, 0, err
}
vfsObj := d.fs.vfsfs.VirtualFilesystem()
upperPop := &vfs.PathOperation{Root: d.upperVD, Start: d.upperVD}

// First, set the ACL on the underlying filesystem
newACL, mode, err := vfsObj.SetPosixACLAt(ctx, creds, upperPop, t, acl, clearSGID)
if err != nil {
return nil, 0, err
}
// overlayfs does not currently support POSIX ACLs.
return nil, 0, linuxerr.EOPNOTSUPP

// Next, update the ACL in our dentry
d.copyMu.Lock()
defer d.copyMu.Unlock()
switch t {
case vfs.AccessACL:
d.accessACL.Store(newACL)
d.mode.Store(uint32(mode))
case vfs.DefaultACL:
d.defaultACL.Store(newACL)
}

return newACL, mode, nil
}

// PrependPath implements vfs.FilesystemImpl.PrependPath.
Expand Down
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