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// Copyright 2018 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/fs"
"gvisor.dev/gvisor/pkg/sentry/kernel"
)
// Mount implements Linux syscall mount(2).
func Mount(t *kernel.Task, 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()
fsType, err := t.CopyInString(typeAddr, hostarch.PageSize)
if err != nil {
return 0, nil, err
}
sourcePath, _, err := copyInPath(t, sourceAddr, true /* allowEmpty */)
if err != nil {
return 0, nil, err
}
targetPath, _, err := copyInPath(t, targetAddr, false /* allowEmpty */)
if err != nil {
return 0, nil, err
}
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
}
}
// 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
}
// Must have CAP_SYS_ADMIN in the mount namespace's associated user
// namespace.
if !t.HasCapabilityIn(linux.CAP_SYS_ADMIN, t.MountNamespace().UserNamespace()) {
return 0, nil, linuxerr.EPERM
}
const unsupportedOps = linux.MS_REMOUNT | linux.MS_BIND |
linux.MS_SHARED | linux.MS_PRIVATE | linux.MS_SLAVE |
linux.MS_UNBINDABLE | linux.MS_MOVE
// Silently allow MS_NOSUID, since we don't implement set-id bits
// anyway.
const unsupportedFlags = linux.MS_NODEV |
linux.MS_NODIRATIME | linux.MS_STRICTATIME
// 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&(unsupportedOps|unsupportedFlags) != 0 {
return 0, nil, linuxerr.EINVAL
}
rsys, ok := fs.FindFilesystem(fsType)
if !ok {
return 0, nil, linuxerr.ENODEV
}
if !rsys.AllowUserMount() {
return 0, nil, linuxerr.EPERM
}
var superFlags fs.MountSourceFlags
if flags&linux.MS_NOATIME == linux.MS_NOATIME {
superFlags.NoAtime = true
}
if flags&linux.MS_RDONLY == linux.MS_RDONLY {
superFlags.ReadOnly = true
}
if flags&linux.MS_NOEXEC == linux.MS_NOEXEC {
superFlags.NoExec = true
}
rootInode, err := rsys.Mount(t, sourcePath, superFlags, data, nil)
if err != nil {
return 0, nil, linuxerr.EINVAL
}
if err := fileOpOn(t, linux.AT_FDCWD, targetPath, true /* resolve */, func(root *fs.Dirent, d *fs.Dirent, _ uint) error {
// Mount will take a reference on rootInode if successful.
return t.MountNamespace().Mount(t, d, rootInode)
}); err != nil {
// Something went wrong. Drop our ref on rootInode before
// returning the error.
rootInode.DecRef(t)
return 0, nil, err
}
return 0, nil, nil
}
// Umount2 implements Linux syscall umount2(2).
func Umount2(t *kernel.Task, args arch.SyscallArguments) (uintptr, *kernel.SyscallControl, error) {
addr := args[0].Pointer()
flags := args[1].Int()
const unsupported = linux.MNT_FORCE | linux.MNT_EXPIRE
if flags&unsupported != 0 {
return 0, nil, linuxerr.EINVAL
}
path, _, err := copyInPath(t, addr, false /* allowEmpty */)
if err != nil {
return 0, nil, err
}
// Must have CAP_SYS_ADMIN in the mount namespace's associated user
// namespace.
//
// Currently, this is always the init task's user namespace.
if !t.HasCapabilityIn(linux.CAP_SYS_ADMIN, t.MountNamespace().UserNamespace()) {
return 0, nil, linuxerr.EPERM
}
resolve := flags&linux.UMOUNT_NOFOLLOW != linux.UMOUNT_NOFOLLOW
detachOnly := flags&linux.MNT_DETACH == linux.MNT_DETACH
return 0, nil, fileOpOn(t, linux.AT_FDCWD, path, resolve, func(root *fs.Dirent, d *fs.Dirent, _ uint) error {
return t.MountNamespace().Unmount(t, d, detachOnly)
})
}
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