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 <dwalsh@redhat.com>

1 files changed, 34 insertions, 33 deletions

diff --git a/pkg/domain/infra/runtime_libpod.go b/pkg/domain/infra/runtime_libpod.go
index dffd90dbe..5fdc252e2 100644
--- a/pkg/domain/infra/runtime_libpod.go
+++ b/pkg/domain/infra/runtime_libpod.go
@@ -276,46 +276,47 @@ func ParseIDMapping(mode namespaces.UsernsMode, uidMapSlice, gidMapSlice []strin
 		if len(subUIDMap) > 0 || len(subGIDMap) > 0 {
 			return nil, errors.New("cannot specify subuidmap or subgidmap with --userns=keep-id")
 		}
-		if rootless.IsRootless() {
-			min := func(a, b int) int {
-				if a < b {
-					return a
-				}
-				return b
+		if !rootless.IsRootless() {
+			return nil, errors.New("keep-id is only supported in rootless mode")
+		}
+		min := func(a, b int) int {
+			if a < b {
+				return a
 			}
+			return b
+		}
 
-			uid := rootless.GetRootlessUID()
-			gid := rootless.GetRootlessGID()
-
-			uids, gids, err := rootless.GetConfiguredMappings()
-			if err != nil {
-				return nil, errors.Wrapf(err, "cannot read mappings")
-			}
-			maxUID, maxGID := 0, 0
-			for _, u := range uids {
-				maxUID += u.Size
-			}
-			for _, g := range gids {
-				maxGID += g.Size
-			}
+		uid := rootless.GetRootlessUID()
+		gid := rootless.GetRootlessGID()
 
-			options.UIDMap, options.GIDMap = nil, nil
+		uids, gids, err := rootless.GetConfiguredMappings()
+		if err != nil {
+			return nil, 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 = 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})
 		}
+
+		options.HostUIDMapping = false
+		options.HostGIDMapping = false
 		// Simply ignore the setting and do not setup an inner namespace for root as it is a no-op
 		return &options, nil
 	}