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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 linux
import (
"gvisor.dev/gvisor/pkg/abi/linux"
"gvisor.dev/gvisor/pkg/errors/linuxerr"
"gvisor.dev/gvisor/pkg/hostarch"
"gvisor.dev/gvisor/pkg/sentry/arch"
"gvisor.dev/gvisor/pkg/sentry/kernel"
"gvisor.dev/gvisor/pkg/sentry/vfs"
)
// Mount implements Linux syscall mount(2).
func Mount(t *kernel.Task, sysno uintptr, args arch.SyscallArguments) (uintptr, *kernel.SyscallControl, error) {
sourceAddr := args[0].Pointer()
targetAddr := args[1].Pointer()
typeAddr := args[2].Pointer()
flags := args[3].Uint64()
dataAddr := args[4].Pointer()
// Must have CAP_SYS_ADMIN in the current mount namespace's associated user
// namespace.
creds := t.Credentials()
if !creds.HasCapabilityIn(linux.CAP_SYS_ADMIN, t.MountNamespace().Owner) {
return 0, nil, linuxerr.EPERM
}
// Ignore magic value that was required before Linux 2.4.
if flags&linux.MS_MGC_MSK == linux.MS_MGC_VAL {
flags = flags &^ linux.MS_MGC_MSK
}
// Silently allow MS_NOSUID, since we don't implement set-id bits anyway.
const unsupported = linux.MS_UNBINDABLE | linux.MS_MOVE | linux.MS_NODIRATIME
// Linux just allows passing any flags to mount(2) - it won't fail when
// unknown or unsupported flags are passed. Since we don't implement
// everything, we fail explicitly on flags that are unimplemented.
if flags&(unsupported) != 0 {
return 0, nil, linuxerr.EINVAL
}
// For null-terminated strings related to mount(2), Linux copies in at most
// a page worth of data. See fs/namespace.c:copy_mount_string().
targetPath, err := copyInPath(t, targetAddr)
if err != nil {
return 0, nil, err
}
target, err := getTaskPathOperation(t, linux.AT_FDCWD, targetPath, disallowEmptyPath, followFinalSymlink)
if err != nil {
return 0, nil, err
}
defer target.Release(t)
var opts vfs.MountOptions
if flags&(linux.MS_NOATIME|linux.MS_STRICTATIME) == linux.MS_NOATIME {
opts.Flags.NoATime = true
}
if flags&linux.MS_NOEXEC == linux.MS_NOEXEC {
opts.Flags.NoExec = true
}
if flags&linux.MS_NODEV == linux.MS_NODEV {
opts.Flags.NoDev = true
}
if flags&linux.MS_NOSUID == linux.MS_NOSUID {
opts.Flags.NoSUID = true
}
if flags&linux.MS_RDONLY == linux.MS_RDONLY {
opts.ReadOnly = true
}
data := ""
if dataAddr != 0 {
// In Linux, a full page is always copied in regardless of null
// character placement, and the address is passed to each file system.
// Most file systems always treat this data as a string, though, and so
// do all of the ones we implement.
data, err = t.CopyInString(dataAddr, hostarch.PageSize)
if err != nil {
return 0, nil, err
}
}
opts.GetFilesystemOptions.Data = data
switch {
case flags&linux.MS_REMOUNT != 0:
// When MS_REMOUNT is specified, the flags and data should match the values used in the original mount() call,
// except for those parameters that are being changed.
//
// The src and filesystem type are ignored for MS_REMOUNT.
return 0, nil, t.Kernel().VFS().RemountAt(t, creds, &target.pop, &opts)
case flags&linux.MS_BIND != 0:
sourcePath, err := copyInPath(t, sourceAddr)
if err != nil {
return 0, nil, err
}
var sourceTpop taskPathOperation
sourceTpop, err = getTaskPathOperation(t, linux.AT_FDCWD, sourcePath, disallowEmptyPath, followFinalSymlink)
if err != nil {
return 0, nil, err
}
defer sourceTpop.Release(t)
return 0, nil, t.Kernel().VFS().BindAt(t, creds, &sourceTpop.pop, &target.pop, flags&linux.MS_REC != 0)
case flags&(linux.MS_SHARED|linux.MS_PRIVATE|linux.MS_SLAVE|linux.MS_UNBINDABLE) != 0:
return 0, nil, t.Kernel().VFS().SetMountPropagationAt(t, creds, &target.pop, uint32(flags))
}
// Only copy in source, fstype, and data if we are doing a normal mount.
var source string
if sourceAddr != 0 {
source, err = t.CopyInString(sourceAddr, hostarch.PageSize)
if err != nil {
return 0, nil, err
}
}
fsType, err := t.CopyInString(typeAddr, hostarch.PageSize)
if err != nil {
return 0, nil, err
}
_, err = t.Kernel().VFS().MountAt(t, creds, source, &target.pop, fsType, &opts)
return 0, nil, err
}
// Umount2 implements Linux syscall umount2(2).
func Umount2(t *kernel.Task, sysno uintptr, args arch.SyscallArguments) (uintptr, *kernel.SyscallControl, error) {
addr := args[0].Pointer()
flags := args[1].Int()
// Must have CAP_SYS_ADMIN in the mount namespace's associated user
// namespace.
//
// Currently, this is always the init task's user namespace.
creds := t.Credentials()
if !creds.HasCapabilityIn(linux.CAP_SYS_ADMIN, t.MountNamespace().Owner) {
return 0, nil, linuxerr.EPERM
}
const unsupported = linux.MNT_FORCE | linux.MNT_EXPIRE
if flags&unsupported != 0 {
return 0, nil, linuxerr.EINVAL
}
path, err := copyInPath(t, addr)
if err != nil {
return 0, nil, err
}
tpop, err := getTaskPathOperation(t, linux.AT_FDCWD, path, disallowEmptyPath, shouldFollowFinalSymlink(flags&linux.UMOUNT_NOFOLLOW == 0))
if err != nil {
return 0, nil, err
}
defer tpop.Release(t)
opts := vfs.UmountOptions{
Flags: uint32(flags &^ linux.UMOUNT_NOFOLLOW),
}
return 0, nil, t.Kernel().VFS().UmountAt(t, creds, &tpop.pop, &opts)
}
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