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// Copyright 2020 The gVisor 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.
// Package memxattr provides a default, in-memory extended attribute
// implementation.
package memxattr
import (
"strings"
"gvisor.dev/gvisor/pkg/abi/linux"
"gvisor.dev/gvisor/pkg/sentry/kernel/auth"
"gvisor.dev/gvisor/pkg/sentry/vfs"
"gvisor.dev/gvisor/pkg/sync"
"gvisor.dev/gvisor/pkg/syserror"
)
// SimpleExtendedAttributes implements extended attributes using a map of
// names to values.
//
// SimpleExtendedAttributes calls vfs.CheckXattrPermissions, so callers are not
// required to do so.
//
// +stateify savable
type SimpleExtendedAttributes struct {
// mu protects the below fields.
mu sync.RWMutex `state:"nosave"`
xattrs map[string]string
}
// GetXattr returns the value at 'name'.
func (x *SimpleExtendedAttributes) GetXattr(creds *auth.Credentials, mode linux.FileMode, kuid auth.KUID, opts *vfs.GetXattrOptions) (string, error) {
if err := vfs.CheckXattrPermissions(creds, vfs.MayRead, mode, kuid, opts.Name); err != nil {
return "", err
}
x.mu.RLock()
value, ok := x.xattrs[opts.Name]
x.mu.RUnlock()
if !ok {
return "", syserror.ENODATA
}
// Check that the size of the buffer provided in getxattr(2) is large enough
// to contain the value.
if opts.Size != 0 && uint64(len(value)) > opts.Size {
return "", syserror.ERANGE
}
return value, nil
}
// SetXattr sets 'value' at 'name'.
func (x *SimpleExtendedAttributes) SetXattr(creds *auth.Credentials, mode linux.FileMode, kuid auth.KUID, opts *vfs.SetXattrOptions) error {
if err := vfs.CheckXattrPermissions(creds, vfs.MayWrite, mode, kuid, opts.Name); err != nil {
return err
}
x.mu.Lock()
defer x.mu.Unlock()
if x.xattrs == nil {
if opts.Flags&linux.XATTR_REPLACE != 0 {
return syserror.ENODATA
}
x.xattrs = make(map[string]string)
}
_, ok := x.xattrs[opts.Name]
if ok && opts.Flags&linux.XATTR_CREATE != 0 {
return syserror.EEXIST
}
if !ok && opts.Flags&linux.XATTR_REPLACE != 0 {
return syserror.ENODATA
}
x.xattrs[opts.Name] = opts.Value
return nil
}
// ListXattr returns all names in xattrs.
func (x *SimpleExtendedAttributes) ListXattr(creds *auth.Credentials, size uint64) ([]string, error) {
// Keep track of the size of the buffer needed in listxattr(2) for the list.
listSize := 0
x.mu.RLock()
names := make([]string, 0, len(x.xattrs))
haveCap := creds.HasCapability(linux.CAP_SYS_ADMIN)
for n := range x.xattrs {
// Hide extended attributes in the "trusted" namespace from
// non-privileged users. This is consistent with Linux's
// fs/xattr.c:simple_xattr_list().
if !haveCap && strings.HasPrefix(n, linux.XATTR_TRUSTED_PREFIX) {
continue
}
names = append(names, n)
// Add one byte per null terminator.
listSize += len(n) + 1
}
x.mu.RUnlock()
if size != 0 && uint64(listSize) > size {
return nil, syserror.ERANGE
}
return names, nil
}
// RemoveXattr removes the xattr at 'name'.
func (x *SimpleExtendedAttributes) RemoveXattr(creds *auth.Credentials, mode linux.FileMode, kuid auth.KUID, name string) error {
if err := vfs.CheckXattrPermissions(creds, vfs.MayWrite, mode, kuid, name); err != nil {
return err
}
x.mu.Lock()
defer x.mu.Unlock()
if _, ok := x.xattrs[name]; !ok {
return syserror.ENODATA
}
delete(x.xattrs, name)
return nil
}
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