98 lines
3.0 KiB
Go
98 lines
3.0 KiB
Go
// Copyright 2018 Google LLC
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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 fs
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import (
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"gvisor.googlesource.com/gvisor/pkg/abi/linux"
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"gvisor.googlesource.com/gvisor/pkg/sentry/context"
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"gvisor.googlesource.com/gvisor/pkg/sentry/kernel/auth"
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)
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// contextID is the fs package's type for context.Context.Value keys.
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type contextID int
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const (
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// CtxRoot is a Context.Value key for a Dirent.
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CtxRoot contextID = iota
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)
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// ContextCanAccessFile determines whether `file` can be accessed in the requested way
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// (for reading, writing, or execution) using the caller's credentials and user
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// namespace, as does Linux's fs/namei.c:generic_permission.
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func ContextCanAccessFile(ctx context.Context, inode *Inode, reqPerms PermMask) bool {
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creds := auth.CredentialsFromContext(ctx)
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uattr, err := inode.UnstableAttr(ctx)
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if err != nil {
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return false
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}
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p := uattr.Perms.Other
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// Are we owner or in group?
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if uattr.Owner.UID == creds.EffectiveKUID {
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p = uattr.Perms.User
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} else if creds.InGroup(uattr.Owner.GID) {
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p = uattr.Perms.Group
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}
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// Are permissions satisfied without capability checks?
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if p.SupersetOf(reqPerms) {
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return true
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}
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if IsDir(inode.StableAttr) {
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// CAP_DAC_OVERRIDE can override any perms on directories.
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if inode.CheckCapability(ctx, linux.CAP_DAC_OVERRIDE) {
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return true
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}
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// CAP_DAC_READ_SEARCH can normally only override Read perms,
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// but for directories it can also override execution.
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if !reqPerms.Write && inode.CheckCapability(ctx, linux.CAP_DAC_READ_SEARCH) {
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return true
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}
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}
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// CAP_DAC_OVERRIDE can always override Read/Write.
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// Can override executable only when at least one execute bit is set.
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if !reqPerms.Execute || uattr.Perms.AnyExecute() {
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if inode.CheckCapability(ctx, linux.CAP_DAC_OVERRIDE) {
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return true
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}
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}
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// Read perms can be overridden by CAP_DAC_READ_SEARCH.
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if reqPerms.OnlyRead() && inode.CheckCapability(ctx, linux.CAP_DAC_READ_SEARCH) {
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return true
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}
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return false
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}
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// FileOwnerFromContext returns a FileOwner using the effective user and group
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// IDs used by ctx.
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func FileOwnerFromContext(ctx context.Context) FileOwner {
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creds := auth.CredentialsFromContext(ctx)
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return FileOwner{creds.EffectiveKUID, creds.EffectiveKGID}
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}
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// RootFromContext returns the root of the virtual filesystem observed by ctx,
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// or nil if ctx is not associated with a virtual filesystem. If
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// RootFromContext returns a non-nil fs.Dirent, a reference is taken on it.
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func RootFromContext(ctx context.Context) *Dirent {
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if v := ctx.Value(CtxRoot); v != nil {
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return v.(*Dirent)
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}
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return nil
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}
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