From 80c0fceb24b70a85f3f2ca8be29f4a131c0881d4 Mon Sep 17 00:00:00 2001 From: Daniel J Walsh Date: Wed, 13 Apr 2022 14:06:05 -0400 Subject: Add support for --userns=nomap From a security point of view, it would be nice to be able to map a rootless usernamespace that does not use your own UID within the container. This would add protection against a hostile process escapping the container and reading content in your homedir. Signed-off-by: Daniel J Walsh --- pkg/util/utils.go | 105 ++++++++++++++++++++++++++++++++++-------------------- 1 file changed, 67 insertions(+), 38 deletions(-) (limited to 'pkg/util') diff --git a/pkg/util/utils.go b/pkg/util/utils.go index b89978601..aed9aebfc 100644 --- a/pkg/util/utils.go +++ b/pkg/util/utils.go @@ -347,55 +347,84 @@ func ParseSignal(rawSignal string) (syscall.Signal, error) { // GetKeepIDMapping returns the mappings and the user to use when keep-id is used func GetKeepIDMapping() (*stypes.IDMappingOptions, int, int, error) { + if !rootless.IsRootless() { + return nil, -1, -1, errors.New("keep-id is only supported in rootless mode") + } options := stypes.IDMappingOptions{ - HostUIDMapping: true, - HostGIDMapping: true, + HostUIDMapping: false, + HostGIDMapping: false, } - uid, gid := 0, 0 - if rootless.IsRootless() { - min := func(a, b int) int { - if a < b { - return a - } - return b + min := func(a, b int) int { + if a < b { + return a } + return b + } - uid = rootless.GetRootlessUID() - gid = rootless.GetRootlessGID() + uid := rootless.GetRootlessUID() + gid := rootless.GetRootlessGID() - uids, gids, err := rootless.GetConfiguredMappings() - if err != nil { - return nil, -1, -1, errors.Wrapf(err, "cannot read mappings") - } - maxUID, maxGID := 0, 0 - for _, u := range uids { - maxUID += u.Size - } - for _, g := range gids { - maxGID += g.Size - } - - options.UIDMap, options.GIDMap = nil, nil + uids, gids, err := rootless.GetConfiguredMappings() + if err != nil { + return nil, -1, -1, errors.Wrapf(err, "cannot read mappings") + } + if len(uids) == 0 || len(gids) == 0 { + return nil, -1, -1, errors.Wrapf(err, "keep-id requires additional UIDs or GIDs defined in /etc/subuid and /etc/subgid to function correctly") + } + maxUID, maxGID := 0, 0 + for _, u := range uids { + maxUID += u.Size + } + for _, g := range gids { + maxGID += g.Size + } - options.UIDMap = append(options.UIDMap, idtools.IDMap{ContainerID: 0, HostID: 1, Size: min(uid, maxUID)}) - options.UIDMap = append(options.UIDMap, idtools.IDMap{ContainerID: uid, HostID: 0, Size: 1}) - if maxUID > uid { - options.UIDMap = append(options.UIDMap, idtools.IDMap{ContainerID: uid + 1, HostID: uid + 1, Size: maxUID - uid}) - } + options.UIDMap, options.GIDMap = nil, nil - options.GIDMap = append(options.GIDMap, idtools.IDMap{ContainerID: 0, HostID: 1, Size: min(gid, maxGID)}) - options.GIDMap = append(options.GIDMap, idtools.IDMap{ContainerID: gid, HostID: 0, Size: 1}) - if maxGID > gid { - options.GIDMap = append(options.GIDMap, idtools.IDMap{ContainerID: gid + 1, HostID: gid + 1, Size: maxGID - gid}) - } + options.UIDMap = append(options.UIDMap, idtools.IDMap{ContainerID: 0, HostID: 1, Size: min(uid, maxUID)}) + options.UIDMap = append(options.UIDMap, idtools.IDMap{ContainerID: uid, HostID: 0, Size: 1}) + if maxUID > uid { + options.UIDMap = append(options.UIDMap, idtools.IDMap{ContainerID: uid + 1, HostID: uid + 1, Size: maxUID - uid}) + } - options.HostUIDMapping = false - options.HostGIDMapping = false + options.GIDMap = append(options.GIDMap, idtools.IDMap{ContainerID: 0, HostID: 1, Size: min(gid, maxGID)}) + options.GIDMap = append(options.GIDMap, idtools.IDMap{ContainerID: gid, HostID: 0, Size: 1}) + if maxGID > gid { + options.GIDMap = append(options.GIDMap, idtools.IDMap{ContainerID: gid + 1, HostID: gid + 1, Size: maxGID - gid}) } - // Simply ignore the setting and do not setup an inner namespace for root as it is a no-op + return &options, uid, gid, nil } +// GetNoMapMapping returns the mappings and the user to use when nomap is used +func GetNoMapMapping() (*stypes.IDMappingOptions, int, int, error) { + if !rootless.IsRootless() { + return nil, -1, -1, errors.New("nomap is only supported in rootless mode") + } + options := stypes.IDMappingOptions{ + HostUIDMapping: false, + HostGIDMapping: false, + } + uids, gids, err := rootless.GetConfiguredMappings() + if err != nil { + return nil, -1, -1, errors.Wrapf(err, "cannot read mappings") + } + if len(uids) == 0 || len(gids) == 0 { + return nil, -1, -1, errors.Wrapf(err, "nomap requires additional UIDs or GIDs defined in /etc/subuid and /etc/subgid to function correctly") + } + options.UIDMap, options.GIDMap = nil, nil + uid, gid := 0, 0 + for _, u := range uids { + options.UIDMap = append(options.UIDMap, idtools.IDMap{ContainerID: uid, HostID: uid + 1, Size: u.Size}) + uid += u.Size + } + for _, g := range gids { + options.GIDMap = append(options.GIDMap, idtools.IDMap{ContainerID: gid, HostID: gid + 1, Size: g.Size}) + gid += g.Size + } + return &options, 0, 0, nil +} + // ParseIDMapping takes idmappings and subuid and subgid maps and returns a storage mapping func ParseIDMapping(mode namespaces.UsernsMode, uidMapSlice, gidMapSlice []string, subUIDMap, subGIDMap string) (*stypes.IDMappingOptions, error) { options := stypes.IDMappingOptions{ @@ -415,7 +444,7 @@ func ParseIDMapping(mode namespaces.UsernsMode, uidMapSlice, gidMapSlice []strin options.AutoUserNsOpts = *opts return &options, nil } - if mode.IsKeepID() { + if mode.IsKeepID() || mode.IsNoMap() { options.HostUIDMapping = false options.HostGIDMapping = false return &options, nil -- cgit v1.2.3-54-g00ecf