1 files changed, 129 insertions, 0 deletions
diff --git a/pkg/sentry/fs/proc/exec_args.go b/pkg/sentry/fs/proc/exec_args.go
new file mode 100644
index 000000000..0e1523bf1
--- /dev/null
+++ b/pkg/sentry/fs/proc/exec_args.go
@@ -0,0 +1,129 @@
+// Copyright 2018 Google Inc.
+//
+// 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 (
+	"fmt"
+	"io"
+
+	"gvisor.googlesource.com/gvisor/pkg/sentry/context"
+	"gvisor.googlesource.com/gvisor/pkg/sentry/fs"
+	"gvisor.googlesource.com/gvisor/pkg/sentry/fs/ramfs"
+	"gvisor.googlesource.com/gvisor/pkg/sentry/kernel"
+	"gvisor.googlesource.com/gvisor/pkg/sentry/usermem"
+	"gvisor.googlesource.com/gvisor/pkg/syserror"
+)
+
+// execArgType enumerates the types of exec arguments that are exposed through
+// proc.
+type execArgType int
+
+const (
+	cmdlineExecArg execArgType = iota
+	environExecArg
+)
+
+// execArgFile is a file containing the exec args (either cmdline or environ)
+// for a given task.
+type execArgFile struct {
+	ramfs.Entry
+
+	// 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
+}
+
+// newExecArgFile creates a file containing the exec args of the given type.
+func newExecArgFile(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 := &execArgFile{
+		arg: arg,
+		t:   t,
+	}
+	f.InitEntry(t, fs.RootOwner, fs.FilePermsFromMode(0444))
+	return newFile(f, msrc, fs.SpecialFile, t)
+}
+
+// DeprecatedPreadv reads the exec arg from the process's address space..
+func (f *execArgFile) DeprecatedPreadv(ctx context.Context, dst usermem.IOSequence, offset int64) (int64, error) {
+	if offset < 0 {
+		return 0, syserror.EINVAL
+	}
+
+	// N.B. Linux 4.2 eliminates the arbitrary one page limit.
+	if offset > usermem.PageSize {
+		return 0, io.EOF
+	}
+	dst = dst.TakeFirst64(usermem.PageSize - offset)
+
+	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, copyErr := m.CopyIn(ctx, start, buf, usermem.IOOpts{})
+	if copyN == 0 {
+		// Nothing to copy.
+		return 0, copyErr
+	}
+	buf = buf[:copyN]
+
+	// TODO: 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.
+
+	n, dstErr := dst.CopyOut(ctx, buf)
+	if dstErr != nil {
+		return int64(n), dstErr
+	}
+	return int64(n), copyErr
+}