diff --git a/CHANGELOG.md b/CHANGELOG.md index 064a0c7bb..a73af8bcb 100644 --- a/CHANGELOG.md +++ b/CHANGELOG.md @@ -23,6 +23,12 @@ and this project adheres to [Semantic Versioning](http://semver.org/). not currently have support for generating them. While this is technically a spec requirement, through testing we've never encountered an actual user of these whiteouts. openSUSE/umoci#224 openSUSE/umoci#229 +- `umoci unpack` will now use some rootless tricks inside user namespaces for + operations that are known to fail (such as `mknod(2)`) while other operations + will be carried out as normal (such as `lchown(2)`). It should be noted that + the `/proc/self/uid_map` checking we do can be tricked into not detecting + user namespaces, but you would need to be trying to break it on purpose. + openSUSE/umoci#171 openSUSE/umoci#230 ### Fixed - Fix a bug in our "parent directory restore" code, which is responsible for diff --git a/oci/layer/tar_extract.go b/oci/layer/tar_extract.go index c7f85306d..528958a2e 100644 --- a/oci/layer/tar_extract.go +++ b/oci/layer/tar_extract.go @@ -30,15 +30,27 @@ import ( "github.com/cyphar/filepath-securejoin" "github.com/openSUSE/umoci/pkg/fseval" "github.com/openSUSE/umoci/pkg/system" + "github.com/openSUSE/umoci/third_party/shared" "github.com/pkg/errors" "golang.org/x/sys/unix" ) +// inUserNamespace is a cached return value of shared.RunningInUserNS(). We +// compute this once globally rather than for each unpack. It won't change (we +// would hope) after we check it the first time. +var inUserNamespace = shared.RunningInUserNS() + type tarExtractor struct { // mapOptions is the set of mapping options to use when extracting // filesystem layers. mapOptions MapOptions + // partialRootless indicates whether "partial rootless" tricks should be + // applied in our extraction. Rootless and userns execution have some + // similar tricks necessary, but not all rootless tricks should be applied + // when running in a userns -- hence the term "partial rootless" tricks. + partialRootless bool + // fsEval is an fseval.FsEval used for extraction. fsEval fseval.FsEval @@ -60,9 +72,10 @@ func newTarExtractor(opt MapOptions) *tarExtractor { } return &tarExtractor{ - mapOptions: opt, - fsEval: fsEval, - upperPaths: make(map[string]struct{}), + mapOptions: opt, + partialRootless: opt.Rootless || inUserNamespace, + fsEval: fsEval, + upperPaths: make(map[string]struct{}), } } @@ -124,7 +137,7 @@ func (te *tarExtractor) restoreMetadata(path string, hdr *tar.Header) error { // In rootless mode, some xattrs will fail (security.capability). // This is _fine_ as long as we're not running as root (in which // case we shouldn't be ignoring xattrs that we were told to set). - if te.mapOptions.Rootless && os.IsPermission(errors.Cause(err)) { + if te.partialRootless && os.IsPermission(errors.Cause(err)) { log.Warnf("rootless{%s} ignoring (usually) harmless EPERM on setxattr %q", hdr.Name, name) continue } @@ -425,8 +438,15 @@ func (te *tarExtractor) unpackEntry(root string, hdr *tar.Header, r io.Reader) ( // character device node, block device node case tar.TypeChar, tar.TypeBlock: - // In rootless mode we have to fake this. - if te.mapOptions.Rootless { + // In rootless mode we have no choice but to fake this, since mknod(2) + // doesn't work as an unprivileged user here. + // + // TODO: We need to add the concept of a fake block device in + // "user.rootlesscontainers", because this workaround suffers + // from the obvious issue that if the file is touched (even the + // metadata) then it will be incorrectly copied into the layer. + // This would break distribution images fairly badly. + if te.partialRootless { log.Warnf("rootless{%s} creating empty file in place of device %d:%d", hdr.Name, hdr.Devmajor, hdr.Devminor) fh, err := te.fsEval.Create(path) if err != nil { diff --git a/third_party/shared/COPYING b/third_party/shared/COPYING new file mode 100644 index 000000000..d64569567 --- /dev/null +++ b/third_party/shared/COPYING @@ -0,0 +1,202 @@ + + Apache License + Version 2.0, January 2004 + http://www.apache.org/licenses/ + + TERMS AND CONDITIONS FOR USE, REPRODUCTION, AND DISTRIBUTION + + 1. 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We also recommend that a + file or class name and description of purpose be included on the + same "printed page" as the copyright notice for easier + identification within third-party archives. + + Copyright [yyyy] [name of copyright owner] + + Licensed under the Apache License, Version 2.0 (the "License"); + you may not use this file except in compliance with the License. + You may obtain a copy of the License at + + http://www.apache.org/licenses/LICENSE-2.0 + + Unless required by applicable law or agreed to in writing, software + distributed under the License is distributed on an "AS IS" BASIS, + WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. + See the License for the specific language governing permissions and + limitations under the License. diff --git a/third_party/shared/util.go b/third_party/shared/util.go new file mode 100644 index 000000000..88cfe1430 --- /dev/null +++ b/third_party/shared/util.go @@ -0,0 +1,54 @@ +/* + * lxd: daemon based on liblxd with a REST API + * Copyright (C) 2015-2017 LXD Authors + * + * Licensed under the Apache License, Version 2.0 (the "License"); + * you may not use this file except in compliance with the License. + * You may obtain a copy of the License at + * + * http://www.apache.org/licenses/LICENSE-2.0 + * + * Unless required by applicable law or agreed to in writing, software + * distributed under the License is distributed on an "AS IS" BASIS, + * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. + * See the License for the specific language governing permissions and + * limitations under the License. + */ + +// This code was copied from https://github.com/lxc/lxd, which is available +// under the the Apache 2.0 license (as noted above). The version of this code +// comes from the tag lxd-2.21 at /shared/util.go. + +package shared + +import ( + "bufio" + "fmt" + "os" +) + +// RunningInUserNS returns whether the current process is (likely) inside a +// user namespace. This has a possible false-negative (where it will return +// false while inside a user namespace if it was intentionally configured to be +// confusing to programs like this). +func RunningInUserNS() bool { + file, err := os.Open("/proc/self/uid_map") + if err != nil { + return false + } + defer file.Close() + + buf := bufio.NewReader(file) + l, _, err := buf.ReadLine() + if err != nil { + return false + } + + line := string(l) + var a, b, c int64 + fmt.Sscanf(line, "%d %d %d", &a, &b, &c) + if a == 0 && b == 0 && c == 4294967295 { + return false + } + return true +}