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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 proc
import (
"bytes"
"fmt"
"io"
"gvisor.dev/gvisor/pkg/abi/linux"
"gvisor.dev/gvisor/pkg/sentry/context"
"gvisor.dev/gvisor/pkg/sentry/fs"
"gvisor.dev/gvisor/pkg/sentry/fs/fsutil"
"gvisor.dev/gvisor/pkg/sentry/kernel"
"gvisor.dev/gvisor/pkg/sentry/usermem"
"gvisor.dev/gvisor/pkg/syserror"
"gvisor.dev/gvisor/pkg/waiter"
)
// execArgType enumerates the types of exec arguments that are exposed through
// proc.
type execArgType int
const (
cmdlineExecArg execArgType = iota
environExecArg
)
// execArgInode is a inode containing the exec args (either cmdline or environ)
// for a given task.
//
// +stateify savable
type execArgInode struct {
fsutil.SimpleFileInode
// arg is the type of exec argument this file contains.
arg execArgType
// t is the Task to read the exec arg line from.
t *kernel.Task
}
var _ fs.InodeOperations = (*execArgInode)(nil)
// newExecArgFile creates a file containing the exec args of the given type.
func newExecArgInode(t *kernel.Task, msrc *fs.MountSource, arg execArgType) *fs.Inode {
if arg != cmdlineExecArg && arg != environExecArg {
panic(fmt.Sprintf("unknown exec arg type %v", arg))
}
f := &execArgInode{
SimpleFileInode: *fsutil.NewSimpleFileInode(t, fs.RootOwner, fs.FilePermsFromMode(0444), linux.PROC_SUPER_MAGIC),
arg: arg,
t: t,
}
return newProcInode(f, msrc, fs.SpecialFile, t)
}
// GetFile implements fs.InodeOperations.GetFile.
func (i *execArgInode) GetFile(ctx context.Context, dirent *fs.Dirent, flags fs.FileFlags) (*fs.File, error) {
return fs.NewFile(ctx, dirent, flags, &execArgFile{
arg: i.arg,
t: i.t,
}), nil
}
// +stateify savable
type execArgFile struct {
fsutil.FileGenericSeek `state:"nosave"`
fsutil.FileNoIoctl `state:"nosave"`
fsutil.FileNoMMap `state:"nosave"`
fsutil.FileNoSplice `state:"nosave"`
fsutil.FileNotDirReaddir `state:"nosave"`
fsutil.FileNoopRelease `state:"nosave"`
fsutil.FileNoopFlush `state:"nosave"`
fsutil.FileNoopFsync `state:"nosave"`
fsutil.FileNoopWrite `state:"nosave"`
fsutil.FileUseInodeUnstableAttr `state:"nosave"`
waiter.AlwaysReady `state:"nosave"`
// arg is the type of exec argument this file contains.
arg execArgType
// t is the Task to read the exec arg line from.
t *kernel.Task
}
var _ fs.FileOperations = (*execArgFile)(nil)
// Read reads the exec arg from the process's address space..
func (f *execArgFile) Read(ctx context.Context, _ *fs.File, dst usermem.IOSequence, offset int64) (int64, error) {
if offset < 0 {
return 0, syserror.EINVAL
}
m, err := getTaskMM(f.t)
if err != nil {
return 0, err
}
defer m.DecUsers(ctx)
// Figure out the bounds of the exec arg we are trying to read.
var execArgStart, execArgEnd usermem.Addr
switch f.arg {
case cmdlineExecArg:
execArgStart, execArgEnd = m.ArgvStart(), m.ArgvEnd()
case environExecArg:
execArgStart, execArgEnd = m.EnvvStart(), m.EnvvEnd()
default:
panic(fmt.Sprintf("unknown exec arg type %v", f.arg))
}
if execArgStart == 0 || execArgEnd == 0 {
// Don't attempt to read before the start/end are set up.
return 0, io.EOF
}
start, ok := execArgStart.AddLength(uint64(offset))
if !ok {
return 0, io.EOF
}
if start >= execArgEnd {
return 0, io.EOF
}
length := int(execArgEnd - start)
if dstlen := dst.NumBytes(); int64(length) > dstlen {
length = int(dstlen)
}
buf := make([]byte, length)
// N.B. Technically this should be usermem.IOOpts.IgnorePermissions = true
// until Linux 4.9 (272ddc8b3735 "proc: don't use FOLL_FORCE for reading
// cmdline and environment").
copyN, err := m.CopyIn(ctx, start, buf, usermem.IOOpts{})
if copyN == 0 {
// Nothing to copy.
return 0, err
}
buf = buf[:copyN]
// On Linux, if the NUL byte at the end of the argument vector has been
// overwritten, it continues reading the environment vector as part of
// the argument vector.
if f.arg == cmdlineExecArg && buf[copyN-1] != 0 {
// Linux will limit the return up to and including the first null character in argv
copyN = bytes.IndexByte(buf, 0)
if copyN == -1 {
copyN = len(buf)
}
// If we found a NUL character in argv, return upto and including that character.
if copyN < len(buf) {
buf = buf[:copyN]
} else { // Otherwise return into envp.
lengthEnvv := int(m.EnvvEnd() - m.EnvvStart())
// Upstream limits the returned amount to one page of slop.
// https://elixir.bootlin.com/linux/v4.20/source/fs/proc/base.c#L208
// we'll return one page total between argv and envp because of the
// above page restrictions.
if lengthEnvv > usermem.PageSize-len(buf) {
lengthEnvv = usermem.PageSize - len(buf)
}
// Make a new buffer to fit the whole thing
tmp := make([]byte, length+lengthEnvv)
copyNE, err := m.CopyIn(ctx, m.EnvvStart(), tmp[copyN:], usermem.IOOpts{})
if err != nil {
return 0, err
}
// Linux will return envp up to and including the first NUL character, so find it.
for i, c := range tmp[copyN:] {
if c == 0 {
copyNE = i
break
}
}
copy(tmp, buf)
buf = tmp[:copyN+copyNE]
}
}
n, dstErr := dst.CopyOut(ctx, buf)
if dstErr != nil {
return int64(n), dstErr
}
return int64(n), err
}
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