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Improve uid shifting via chown. #44

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Nov 29, 2021
Merged

Improve uid shifting via chown. #44

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47 changes: 12 additions & 35 deletions idShiftUtils/idShiftUtils.go
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Original file line number Diff line number Diff line change
Expand Up @@ -33,13 +33,6 @@ import (
mapset "github.com/deckarep/golang-set"
)

type OffsetType int

const (
OffsetAdd OffsetType = iota
OffsetSub
)

type aclType int

const (
Expand All @@ -48,7 +41,7 @@ const (
)

// Shifts the ACL type user and group IDs by the given offset
func shiftAclType(aclT aclType, path string, uidOffset, gidOffset uint32, offsetDir OffsetType) error {
func shiftAclType(aclT aclType, path string, uidOffset, gidOffset int32) error {
var facl aclLib.ACL
var err error

Expand Down Expand Up @@ -77,13 +70,8 @@ func shiftAclType(aclT aclType, path string, uidOffset, gidOffset uint32, offset
continue
}

if offsetDir == OffsetAdd {
uid = uid + uint64(uidOffset)
} else {
uid = uid - uint64(uidOffset)
}

e.Qualifier = strconv.FormatUint(uid, 10)
targetUid := uint64(int32(uid) + uidOffset)
e.Qualifier = strconv.FormatUint(targetUid, 10)
aclShifted = true
}

Expand All @@ -95,13 +83,8 @@ func shiftAclType(aclT aclType, path string, uidOffset, gidOffset uint32, offset
continue
}

if offsetDir == OffsetAdd {
gid = gid + uint64(gidOffset)
} else {
gid = gid - uint64(gidOffset)
}

e.Qualifier = strconv.FormatUint(gid, 10)
targetGid := uint64(int32(gid) + gidOffset)
e.Qualifier = strconv.FormatUint(targetGid, 10)
aclShifted = true
}

Expand Down Expand Up @@ -129,17 +112,17 @@ func shiftAclType(aclT aclType, path string, uidOffset, gidOffset uint32, offset
}

// Shifts the ACL user and group IDs by the given offset, both for access and default ACLs
func shiftAclIds(path string, isDir bool, uidOffset, gidOffset uint32, offsetDir OffsetType) error {
func shiftAclIds(path string, isDir bool, uidOffset, gidOffset int32) error {

// Access list
err := shiftAclType(aclTypeAccess, path, uidOffset, gidOffset, offsetDir)
err := shiftAclType(aclTypeAccess, path, uidOffset, gidOffset)
if err != nil {
return err
}

// Default list (for directories only)
if isDir {
err = shiftAclType(aclTypeDefault, path, uidOffset, gidOffset, offsetDir)
err = shiftAclType(aclTypeDefault, path, uidOffset, gidOffset)
if err != nil {
return err
}
Expand All @@ -150,13 +133,12 @@ func shiftAclIds(path string, isDir bool, uidOffset, gidOffset uint32, offsetDir

// "Shifts" ownership of user and group IDs on the given directory and files and directories
// below it by the given offset, using chown.
func ShiftIdsWithChown(baseDir string, uidOffset, gidOffset uint32, offsetDir OffsetType) error {
func ShiftIdsWithChown(baseDir string, uidOffset, gidOffset int32) error {

hardLinks := []uint64{}

err := godirwalk.Walk(baseDir, &godirwalk.Options{
Callback: func(path string, de *godirwalk.Dirent) error {
var targetUid, targetGid uint32

// When doing the chown, we don't follow symlinks as we want to change
// the ownership of the symlinks themselves. We will chown the
Expand Down Expand Up @@ -184,13 +166,8 @@ func ShiftIdsWithChown(baseDir string, uidOffset, gidOffset uint32, offsetDir Of
hardLinks = append(hardLinks, st.Ino)
}

if offsetDir == OffsetAdd {
targetUid = st.Uid + uidOffset
targetGid = st.Gid + gidOffset
} else {
targetUid = st.Uid - uidOffset
targetGid = st.Gid - gidOffset
}
targetUid := int32(st.Uid) + uidOffset
targetGid := int32(st.Gid) + gidOffset

logrus.Debugf("chown %s from %d:%d to %d:%d", path, st.Uid, st.Gid, targetUid, targetGid)

Expand All @@ -203,7 +180,7 @@ func ShiftIdsWithChown(baseDir string, uidOffset, gidOffset uint32, offsetDir Of
// the Linux access control list (ACL) for the file

if fi.Mode()&os.ModeSymlink == 0 {
if err := shiftAclIds(path, fi.IsDir(), uidOffset, gidOffset, offsetDir); err != nil {
if err := shiftAclIds(path, fi.IsDir(), uidOffset, gidOffset); err != nil {
return fmt.Errorf("failed to shift ACL for %s: %s", path, err)
}
}
Expand Down
22 changes: 10 additions & 12 deletions mgr.go
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Original file line number Diff line number Diff line change
Expand Up @@ -476,15 +476,13 @@ func (mgr *SysboxMgr) unregister(id string) error {
// revert mount prep actions
for _, revInfo := range info.mntPrepRev {
if revInfo.uidShifted {
logrus.Infof("reverting uid-shift on %s for %s", revInfo.path, formatter.ContainerID{id})

// revInfo.targetUid is guaranteed to be higher than revInfo.origUid
// (we checked in prepMounts())
uidOffset := int32(revInfo.origUid) - int32(revInfo.targetUid)
gidOffset := int32(revInfo.origGid) - int32(revInfo.targetGid)

uidOffset := revInfo.targetUid - revInfo.origUid
gidOffset := revInfo.targetGid - revInfo.origGid
logrus.Infof("reverting uid-shift on %s for %s (%d -> %d)", revInfo.path, formatter.ContainerID{id}, revInfo.targetUid, revInfo.origUid)

if err = idShiftUtils.ShiftIdsWithChown(revInfo.path, uidOffset, gidOffset, idShiftUtils.OffsetSub); err != nil {
if err = idShiftUtils.ShiftIdsWithChown(revInfo.path, uidOffset, gidOffset); err != nil {
logrus.Warnf("failed to revert uid-shift of mount source at %s: %s", revInfo.path, err)
}

Expand Down Expand Up @@ -837,15 +835,15 @@ func (mgr *SysboxMgr) prepMounts(id string, uid, gid uint32, prepList []ipcLib.M
}

if needUidShift {
logrus.Infof("shifting uids at %s for %s", src, formatter.ContainerID{id})

// uid is guaranteed to be higher than origUid (we checked in
// mntSrcUidShiftNeeded())
// Offset may be positive or negative
uidOffset := int32(uid) - int32(origUid)
gidOffset := int32(gid) - int32(origGid)

uidOffset := uid - origUid
gidOffset := gid - origGid
logrus.Infof("shifting uids at %s for %s (%d -> %d)", src, formatter.ContainerID{id}, origUid, uid)

if err = idShiftUtils.ShiftIdsWithChown(src, uidOffset, gidOffset, idShiftUtils.OffsetAdd); err != nil {
// TODO: for kernel >= 5.12, we need to do this using the new ID-mapped mount feature (faster, more reliable).
if err = idShiftUtils.ShiftIdsWithChown(src, uidOffset, gidOffset); err != nil {
return fmt.Errorf("failed to shift uids via chown for mount source at %s: %s", src, err)
}

Expand Down
36 changes: 8 additions & 28 deletions utils.go
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Original file line number Diff line number Diff line change
Expand Up @@ -723,28 +723,13 @@ func mntSrcUidShiftNeeded(mntSrc string, uid, gid uint32) (bool, uint32, uint32,
mntSrcUid = st.Uid
mntSrcGid = st.Gid

// If the host uid assigned to the container is higher than the uid
// of the dir being mounted into the container, then we perform uid
// If the host uid assigned to the container's root user differs from the
// uid of the dir being mounted into the container, then we perform uid
// shifting. Same for gid.
if uid > mntSrcUid && gid > mntSrcGid {
if uid != mntSrcUid && gid != mntSrcGid {
return true, mntSrcUid, mntSrcGid, nil
}

// If the host uid assigned to the container is lower than the uid of the dir
// being mounted, we skip the uid shift. This is in fact an anomalous case
// because in general the host dir being mounted into the container should
// have host range uids (e.g., 0->65535) and these are usually lower than the
// uids assigned to the container (which come from the subuid ranges in
// /etc/subuid).
if uid < mntSrcUid || gid < mntSrcGid {

logrus.Infof("skipping uid shift on %s because its uid:gid (%d:%d) is "+
"> the container's assigned uid:gid (%d:%d)",
mntSrc, mntSrcUid, mntSrcGid, uid, gid)

return false, mntSrcUid, mntSrcGid, nil
}

// If the mount dir has same ownership as the container, check the subdirs
// before we make a determination on whether ownership shifting will be
// required.
Expand All @@ -755,21 +740,16 @@ func mntSrcUidShiftNeeded(mntSrc string, uid, gid uint32) (bool, uint32, uint32,
return false, 0, 0, err
}

needChown := true
numNeedChown := 0
for _, fi := range dirFis {
st, _ := fi.Sys().(*syscall.Stat_t)

if uid <= st.Uid && gid <= st.Gid {

logrus.Infof("skipping uid shift on %s because subdir %s has uid:gid (%d:%d) which is "+
">= the container's assigned uid:gid (%d:%d)",
mntSrc, fi.Name(), st.Uid, st.Gid, uid, gid)

needChown = false
break
if uid != st.Uid || gid != st.Gid {
numNeedChown += 1
}
}

needChown := (numNeedChown == len(dirFis))

return needChown, mntSrcUid, mntSrcGid, nil
}

Expand Down