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// Copyright 2019 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 linux
import (
"strings"
"gvisor.dev/gvisor/pkg/abi/linux"
"gvisor.dev/gvisor/pkg/sentry/arch"
"gvisor.dev/gvisor/pkg/sentry/fs"
"gvisor.dev/gvisor/pkg/sentry/kernel"
"gvisor.dev/gvisor/pkg/sentry/usermem"
"gvisor.dev/gvisor/pkg/syserror"
)
// GetXattr implements linux syscall getxattr(2).
func GetXattr(t *kernel.Task, args arch.SyscallArguments) (uintptr, *kernel.SyscallControl, error) {
pathAddr := args[0].Pointer()
nameAddr := args[1].Pointer()
valueAddr := args[2].Pointer()
size := uint64(args[3].SizeT())
path, dirPath, err := copyInPath(t, pathAddr, false /* allowEmpty */)
if err != nil {
return 0, nil, err
}
valueLen := 0
err = fileOpOn(t, linux.AT_FDCWD, path, true /* resolve */, func(root *fs.Dirent, d *fs.Dirent, _ uint) error {
// If getxattr(2) is called with size 0, the size of the value will be
// returned successfully even if it is nonzero. In that case, we need to
// retrieve the entire attribute value so we can return the correct size.
requestedSize := size
if size == 0 || size > linux.XATTR_SIZE_MAX {
requestedSize = linux.XATTR_SIZE_MAX
}
value, err := getXattr(t, d, dirPath, nameAddr, uint64(requestedSize))
if err != nil {
return err
}
valueLen = len(value)
if uint64(valueLen) > requestedSize {
return syserror.ERANGE
}
// Skip copying out the attribute value if size is 0.
if size == 0 {
return nil
}
_, err = t.CopyOutBytes(valueAddr, []byte(value))
return err
})
if err != nil {
return 0, nil, err
}
return uintptr(valueLen), nil, nil
}
// getXattr implements getxattr(2) from the given *fs.Dirent.
func getXattr(t *kernel.Task, d *fs.Dirent, dirPath bool, nameAddr usermem.Addr, size uint64) (string, error) {
if dirPath && !fs.IsDir(d.Inode.StableAttr) {
return "", syserror.ENOTDIR
}
if err := checkXattrPermissions(t, d.Inode, fs.PermMask{Read: true}); err != nil {
return "", err
}
name, err := copyInXattrName(t, nameAddr)
if err != nil {
return "", err
}
if !strings.HasPrefix(name, linux.XATTR_USER_PREFIX) {
return "", syserror.EOPNOTSUPP
}
return d.Inode.GetXattr(t, name, size)
}
// SetXattr implements linux syscall setxattr(2).
func SetXattr(t *kernel.Task, args arch.SyscallArguments) (uintptr, *kernel.SyscallControl, error) {
pathAddr := args[0].Pointer()
nameAddr := args[1].Pointer()
valueAddr := args[2].Pointer()
size := uint64(args[3].SizeT())
flags := args[4].Uint()
path, dirPath, err := copyInPath(t, pathAddr, false /* allowEmpty */)
if err != nil {
return 0, nil, err
}
if flags&^(linux.XATTR_CREATE|linux.XATTR_REPLACE) != 0 {
return 0, nil, syserror.EINVAL
}
return 0, nil, fileOpOn(t, linux.AT_FDCWD, path, true /* resolve */, func(root *fs.Dirent, d *fs.Dirent, _ uint) error {
return setXattr(t, d, dirPath, nameAddr, valueAddr, uint64(size), flags)
})
}
// setXattr implements setxattr(2) from the given *fs.Dirent.
func setXattr(t *kernel.Task, d *fs.Dirent, dirPath bool, nameAddr, valueAddr usermem.Addr, size uint64, flags uint32) error {
if dirPath && !fs.IsDir(d.Inode.StableAttr) {
return syserror.ENOTDIR
}
if err := checkXattrPermissions(t, d.Inode, fs.PermMask{Write: true}); err != nil {
return err
}
name, err := copyInXattrName(t, nameAddr)
if err != nil {
return err
}
if size > linux.XATTR_SIZE_MAX {
return syserror.E2BIG
}
buf := make([]byte, size)
if _, err = t.CopyInBytes(valueAddr, buf); err != nil {
return err
}
value := string(buf)
if !strings.HasPrefix(name, linux.XATTR_USER_PREFIX) {
return syserror.EOPNOTSUPP
}
return d.Inode.SetXattr(t, d, name, value, flags)
}
func copyInXattrName(t *kernel.Task, nameAddr usermem.Addr) (string, error) {
name, err := t.CopyInString(nameAddr, linux.XATTR_NAME_MAX+1)
if err != nil {
if err == syserror.ENAMETOOLONG {
return "", syserror.ERANGE
}
return "", err
}
if len(name) == 0 {
return "", syserror.ERANGE
}
return name, nil
}
func checkXattrPermissions(t *kernel.Task, i *fs.Inode, perms fs.PermMask) error {
// Restrict xattrs to regular files and directories.
//
// In Linux, this restriction technically only applies to xattrs in the
// "user.*" namespace, but we don't allow any other xattr prefixes anyway.
if !fs.IsRegular(i.StableAttr) && !fs.IsDir(i.StableAttr) {
if perms.Write {
return syserror.EPERM
}
return syserror.ENODATA
}
return i.CheckPermission(t, perms)
}
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