mirror of
https://github.com/hanzoai/visor.git
synced 2026-09-24 17:04:14 +00:00
Ryan El Kochta
435549c32d
Implements POSIX ACLs for gVisor's tmpfs. As a summary: - Adds `acl` and `defaultACL` fields to tmpfs's inode - Allows `system.posix_acl_access` and `system.posix_acl_default` xattrs to set and retrieve POSIX ACLs - Updates tmpfs's stat implementation to account for the ACL in setting/retrieving a file's mode - Updates `GenericCheckPermission` to take an optional ACL. All non-tmpfs filesystems pass the `nil` ACL. - Updates tmpfs's tar save-and-restore logic to store the base64-encoded POSIX ACL xattrs in the tar header - Adds unit tests for POSIX ACL parsing/serialization - Adds integration tests for POSIX ACLs - Adds a container test to verify the tmpfs tar save/restore logic with ACLs. This required a new subcommand for `test_app` to set and fetch xattrs in the container The motivation for POSIX ACLs is for journald (which uses POSIX ACLs to give non-root users access to their own `systemctl --user` services' logs). This commit is not actually sufficient to get this working -- we will need to plumb ACLs to overlayfs, too, which will be done in a follow-up commit. The implementation is very similar to the implementation in Linux, although it is filesystem-specific rather than at the VFS layer (much like we store `mode`, `uid`, `gid`, etc at the FS layer currently). An optional access and default ACL is stored in each inode. If present, it is used for permission checks and is kept in sync with the `mode`. The `mode` is computed from the ACL when permissions are updated. If the ACL is simple enough to be stored equivalently as a `mode`, an ACL is not stored. One limitation at the moment is that upon file creation, the process's umask is masked against the creation mode regardless of the presence of a default ACL, whereas Linux only masks against umask when *not* inheriting from a default ACL. Fixing this would require a fair bit of refactoring since umask isn't passed through to filesystems at all, and is instead masked with the creation mode at the syscall layer. This is not a security issue since the resulting permissions are always of equal-or-greater restrictiveness to those of Linux, but is tracked in \#13688.
154 lines
4.1 KiB
Go
154 lines
4.1 KiB
Go
// Copyright 2019 The gVisor Authors.
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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package linux
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import (
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"encoding/binary"
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"structs"
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)
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// Constants for extended attributes.
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const (
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XATTR_NAME_MAX = 255
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XATTR_SIZE_MAX = 65536
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XATTR_LIST_MAX = 65536
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XATTR_CREATE = 1
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XATTR_REPLACE = 2
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XATTR_SECURITY_PREFIX = "security."
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XATTR_SECURITY_PREFIX_LEN = len(XATTR_SECURITY_PREFIX)
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XATTR_SECURITY_CAPABILITY = XATTR_SECURITY_PREFIX + "capability"
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XATTR_SYSTEM_PREFIX = "system."
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XATTR_SYSTEM_PREFIX_LEN = len(XATTR_SYSTEM_PREFIX)
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XATTR_TRUSTED_PREFIX = "trusted."
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XATTR_TRUSTED_PREFIX_LEN = len(XATTR_TRUSTED_PREFIX)
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XATTR_USER_PREFIX = "user."
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XATTR_USER_PREFIX_LEN = len(XATTR_USER_PREFIX)
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)
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// Constants for POSIX ACL extended attributes.
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const (
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// Extended attribute names for POSIX ACLs.
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XATTR_NAME_POSIX_ACL_ACCESS = XATTR_SYSTEM_PREFIX + "posix_acl_access"
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XATTR_NAME_POSIX_ACL_DEFAULT = XATTR_SYSTEM_PREFIX + "posix_acl_default"
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POSIX_ACL_XATTR_VERSION = 2
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// ACL_UNDEFINED_ID is the ID for entries that do not contain a
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// named user or group.
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ACL_UNDEFINED_ID = 0xffffffff
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// ACL entry tags.
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ACL_USER_OBJ = 0x01
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ACL_USER = 0x02
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ACL_GROUP_OBJ = 0x04
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ACL_GROUP = 0x08
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ACL_MASK = 0x10
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ACL_OTHER = 0x20
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// ACL entry permission bits.
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ACL_READ = 0x04
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ACL_WRITE = 0x02
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ACL_EXECUTE = 0x01
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)
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// PosixACLXattrEntry is a single entry in the userspace representation
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// of a POSIX ACL. It corresponds to Linux's struct posix_acl_xattr_entry.
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//
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// All fields in PosixACLXattrEntry are stored as little-endian.
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//
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// +marshal dynamic
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type PosixACLXattrEntry struct {
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_ structs.HostLayout
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Tag uint16
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Perm uint16
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ID uint32
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}
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// SizeBytes implements marshal.Marshallable.SizeBytes.
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func (a *PosixACLXattrEntry) SizeBytes() int {
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return 8
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}
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// MarshalBytes implements marshal.Marshallable.MarshalBytes.
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func (a *PosixACLXattrEntry) MarshalBytes(dst []byte) []byte {
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binary.LittleEndian.PutUint16(dst[0:], a.Tag)
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binary.LittleEndian.PutUint16(dst[2:], a.Perm)
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binary.LittleEndian.PutUint32(dst[4:], a.ID)
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return dst[8:]
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}
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// UnmarshalBytes implements marshal.Marshallable.UnmarshalBytes.
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func (a *PosixACLXattrEntry) UnmarshalBytes(src []byte) []byte {
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a.Tag = binary.LittleEndian.Uint16(src[0:])
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a.Perm = binary.LittleEndian.Uint16(src[2:])
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a.ID = binary.LittleEndian.Uint32(src[4:])
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return src[8:]
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}
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// PosixACLXattr is the userspace representation of a POSIX ACL.
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//
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// +marshal dynamic
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type PosixACLXattr struct {
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_ structs.HostLayout
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// Version is the POSIX ACL version, stored as little-endian.
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Version uint32
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// Entries contains the ACL entries.
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Entries []PosixACLXattrEntry `hostlayout:"ignore"`
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}
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// posixACLXattrHeaderSize is the size in bytes of the header.
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const posixACLXattrHeaderSize = 4
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// SizeBytes implements marshal.Marshallable.SizeBytes.
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func (a *PosixACLXattr) SizeBytes() int {
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return posixACLXattrHeaderSize + len(a.Entries)*(*PosixACLXattrEntry)(nil).SizeBytes()
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}
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// MarshalBytes implements marshal.Marshallable.MarshalBytes.
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func (a *PosixACLXattr) MarshalBytes(dst []byte) []byte {
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binary.LittleEndian.PutUint32(dst, a.Version)
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dst = dst[posixACLXattrHeaderSize:]
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for _, entry := range a.Entries {
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dst = entry.MarshalBytes(dst)
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}
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return dst
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}
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// UnmarshalBytes implements marshal.Marshallable.UnmarshalBytes.
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func (a *PosixACLXattr) UnmarshalBytes(src []byte) []byte {
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a.Version = binary.LittleEndian.Uint32(src)
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src = src[posixACLXattrHeaderSize:]
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for len(src) >= (*PosixACLXattrEntry)(nil).SizeBytes() {
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var entry PosixACLXattrEntry
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src = entry.UnmarshalBytes(src)
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a.Entries = append(a.Entries, entry)
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}
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return src
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}
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