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overlayfs: implement POSIX ACLs #13946

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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
58 changes: 56 additions & 2 deletions 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 +181,18 @@ func (d *dentry) copyUpMaybeSyntheticMountpointLocked(ctx context.Context, forSy
cleanupUndoCopyUp()
return err
}
acl := d.accessACL.Load()
newACL, newMode, err := newFD.SetPosixACL(ctx, vfs.AccessACL, acl, false /* clearSGID */)
if err == nil {
d.accessACL.Store(newACL)
d.mode.Store(uint32(newMode))
} else if acl == nil && linuxerr.Equals(linuxerr.EOPNOTSUPP, err) {
// Tolerate EOPNOTSUPP for nil ACLs since if the upper filesystem
// doesn't support ACLs, all files have an implicit nil ACL
} else {
cleanupUndoCopyUp()
return err
}
d.upperVD = newFD.VirtualDentry()
d.upperVD.IncRef()

Expand All @@ -207,6 +219,29 @@ func (d *dentry) copyUpMaybeSyntheticMountpointLocked(ctx context.Context, forSy
cleanupUndoCopyUp()
return err
}
acl := d.accessACL.Load()
newACL, newMode, err := vfsObj.SetPosixACLAt(ctx, d.fs.creds, &newpop, vfs.AccessACL, acl, false /* clearSGID */)
if err == nil {
d.accessACL.Store(newACL)
d.mode.Store(uint32(newMode))
} else if acl == nil && linuxerr.Equals(linuxerr.EOPNOTSUPP, err) {
// Tolerate EOPNOTSUPP for nil ACLs since if the upper filesystem
// doesn't support ACLs, all files have an implicit nil ACL
} else {
cleanupUndoCopyUp()
return err
}
defaultACL := d.defaultACL.Load()
newDefaultACL, _, err := vfsObj.SetPosixACLAt(ctx, d.fs.creds, &newpop, vfs.DefaultACL, defaultACL, false /* clearSGID */)
if err == nil {
d.defaultACL.Store(newDefaultACL)
} else if defaultACL == nil && linuxerr.Equals(linuxerr.EOPNOTSUPP, err) {
// Tolerate EOPNOTSUPP for nil ACLs since if the upper filesystem
// doesn't support ACLs, all files have an implicit nil ACL
} else {
cleanupUndoCopyUp()
return err
}
upperVD, err := vfsObj.GetDentryAt(ctx, d.fs.creds, &newpop, &vfs.GetDentryOptions{})
if err != nil {
cleanupUndoCopyUp()
Expand Down Expand Up @@ -236,6 +271,7 @@ func (d *dentry) copyUpMaybeSyntheticMountpointLocked(ctx context.Context, forSy
cleanupUndoCopyUp()
return err
}
// Skip POSIX ACLs since symlinks cannot have them.
upperVD, err := vfsObj.GetDentryAt(ctx, d.fs.creds, &newpop, &vfs.GetDentryOptions{})
if err != nil {
cleanupUndoCopyUp()
Expand All @@ -254,8 +290,9 @@ func (d *dentry) copyUpMaybeSyntheticMountpointLocked(ctx context.Context, forSy
}
if err := vfsObj.SetStatAt(ctx, d.fs.creds, &newpop, &vfs.SetStatOptions{
Stat: linux.Statx{
Mask: linux.STATX_UID | linux.STATX_GID | oldStat.Mask&timestampsMask,
Mask: linux.STATX_MODE | linux.STATX_UID | linux.STATX_GID | oldStat.Mask&timestampsMask,
// d.uid and d.gid can be read because d.copyMu is locked.
Mode: uint16(d.mode.RacyLoad()),
UID: d.uid.RacyLoad(),
GID: d.gid.RacyLoad(),
Atime: oldStat.Atime,
Expand All @@ -265,6 +302,18 @@ func (d *dentry) copyUpMaybeSyntheticMountpointLocked(ctx context.Context, forSy
cleanupUndoCopyUp()
return err
}
acl := d.accessACL.Load()
newACL, newMode, err := vfsObj.SetPosixACLAt(ctx, d.fs.creds, &newpop, vfs.AccessACL, acl, false /* clearSGID */)
if err == nil {
d.accessACL.Store(newACL)
d.mode.Store(uint32(newMode))
} else if acl == nil && linuxerr.Equals(linuxerr.EOPNOTSUPP, err) {
// Tolerate EOPNOTSUPP for nil ACLs since if the upper filesystem
// doesn't support ACLs, all files have an implicit nil ACL
} else {
cleanupUndoCopyUp()
return err
}
upperVD, err := vfsObj.GetDentryAt(ctx, d.fs.creds, &newpop, &vfs.GetDentryOptions{})
if err != nil {
cleanupUndoCopyUp()
Expand Down Expand Up @@ -375,7 +424,7 @@ 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 +456,11 @@ 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
132 changes: 121 additions & 11 deletions pkg/sentry/fsimpl/overlay/filesystem.go
View file
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Original file line number Diff line number Diff line change
Expand Up @@ -226,10 +226,11 @@ 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 {
Expand Down Expand Up @@ -273,7 +274,22 @@ func (fs *filesystem) lookupLocked(ctx context.Context, parent *dentry, name str
} else {
topLookupLayer = lookupLayerLower
}

// Fetch POSIX ACLs.
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
}

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 @@ -1506,7 +1522,7 @@ 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 @@ -1764,6 +1780,13 @@ 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 @@ -1800,8 +1823,20 @@ 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 @@ -1844,8 +1879,19 @@ 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 @@ -1873,22 +1919,86 @@ 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
}
return fs.getPosixACLLocked(ctx, d, t)
}

func (fs *filesystem) getPosixACLLocked(ctx context.Context, d *dentry, t vfs.ACLType) (*vfs.PosixACL, error) {
switch t {
case vfs.AccessACL:
return d.accessACL.Load(), nil
case vfs.DefaultACL:
return d.defaultACL.Load(), nil
default:
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) {
// Skip ACL update when clearing an already-missing ACL (to prevent unnecessary copy-up)
oldACL, err := fs.getPosixACLLocked(ctx, d, t)
if err != nil {
return nil, 0, err
}
// Take copyMu to check d.upperVD. Technically d could be copied up between here and the later
// call to d.copyUpLocked(), but this would have no effect.
d.copyMu.RLock()
copiedUp := d.upperVD.Ok()
d.copyMu.RUnlock()
if acl == nil && oldACL == nil && !copiedUp {
mode := linux.FileMode(d.mode.Load())
if t == vfs.DefaultACL && !mode.IsDir() {
return nil, 0, nil
}
// ENODATA to match Linux.
return nil, 0, linuxerr.ENODATA
}

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
d.copyMu.Lock()
defer d.copyMu.Unlock()
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
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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