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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 user
import (
"fmt"
"path"
"strings"
"gvisor.dev/gvisor/pkg/abi/linux"
"gvisor.dev/gvisor/pkg/context"
"gvisor.dev/gvisor/pkg/fspath"
"gvisor.dev/gvisor/pkg/log"
"gvisor.dev/gvisor/pkg/sentry/fs"
"gvisor.dev/gvisor/pkg/sentry/kernel"
"gvisor.dev/gvisor/pkg/sentry/kernel/auth"
"gvisor.dev/gvisor/pkg/sentry/vfs"
"gvisor.dev/gvisor/pkg/syserror"
)
// ResolveExecutablePath resolves the given executable name given the working
// dir and environment.
func ResolveExecutablePath(ctx context.Context, args *kernel.CreateProcessArgs) (string, error) {
name := args.Filename
if len(name) == 0 {
if len(args.Argv) == 0 {
return "", fmt.Errorf("no filename or command provided")
}
name = args.Argv[0]
}
// Absolute paths can be used directly.
if path.IsAbs(name) {
return name, nil
}
// Paths with '/' in them should be joined to the working directory, or
// to the root if working directory is not set.
if strings.IndexByte(name, '/') > 0 {
wd := args.WorkingDirectory
if wd == "" {
wd = "/"
}
if !path.IsAbs(wd) {
return "", fmt.Errorf("working directory %q must be absolute", wd)
}
return path.Join(wd, name), nil
}
// Otherwise, We must lookup the name in the paths.
paths := getPath(args.Envv)
if kernel.VFS2Enabled {
f, err := resolveVFS2(ctx, args.Credentials, args.MountNamespaceVFS2, paths, name)
if err != nil {
return "", fmt.Errorf("error finding executable %q in PATH %v: %v", name, paths, err)
}
return f, nil
}
f, err := resolve(ctx, args.MountNamespace, paths, name)
if err != nil {
return "", fmt.Errorf("error finding executable %q in PATH %v: %v", name, paths, err)
}
return f, nil
}
func resolve(ctx context.Context, mns *fs.MountNamespace, paths []string, name string) (string, error) {
root := fs.RootFromContext(ctx)
if root == nil {
// Caller has no root. Don't bother traversing anything.
return "", syserror.ENOENT
}
defer root.DecRef(ctx)
for _, p := range paths {
if !path.IsAbs(p) {
// Relative paths aren't safe, no one should be using them.
log.Warningf("Skipping relative path %q in $PATH", p)
continue
}
binPath := path.Join(p, name)
traversals := uint(linux.MaxSymlinkTraversals)
d, err := mns.FindInode(ctx, root, nil, binPath, &traversals)
if err == syserror.ENOENT || err == syserror.EACCES {
// Didn't find it here.
continue
}
if err != nil {
return "", err
}
defer d.DecRef(ctx)
// Check that it is a regular file.
if !fs.IsRegular(d.Inode.StableAttr) {
continue
}
// Check whether we can read and execute the found file.
if err := d.Inode.CheckPermission(ctx, fs.PermMask{Read: true, Execute: true}); err != nil {
log.Infof("Found executable at %q, but user cannot execute it: %v", binPath, err)
continue
}
return path.Join("/", p, name), nil
}
// Couldn't find it.
return "", syserror.ENOENT
}
func resolveVFS2(ctx context.Context, creds *auth.Credentials, mns *vfs.MountNamespace, paths []string, name string) (string, error) {
root := mns.Root()
root.IncRef()
defer root.DecRef(ctx)
for _, p := range paths {
if !path.IsAbs(p) {
// Relative paths aren't safe, no one should be using them.
log.Warningf("Skipping relative path %q in $PATH", p)
continue
}
binPath := path.Join(p, name)
pop := &vfs.PathOperation{
Root: root,
Start: root,
Path: fspath.Parse(binPath),
FollowFinalSymlink: true,
}
opts := &vfs.OpenOptions{
FileExec: true,
Flags: linux.O_RDONLY,
}
dentry, err := root.Mount().Filesystem().VirtualFilesystem().OpenAt(ctx, creds, pop, opts)
if err == syserror.ENOENT || err == syserror.EACCES {
// Didn't find it here.
continue
}
if err != nil {
return "", err
}
dentry.DecRef(ctx)
return binPath, nil
}
// Couldn't find it.
return "", syserror.ENOENT
}
// getPath returns the PATH as a slice of strings given the environment
// variables.
func getPath(env []string) []string {
const prefix = "PATH="
for _, e := range env {
if strings.HasPrefix(e, prefix) {
return strings.Split(strings.TrimPrefix(e, prefix), ":")
}
}
return nil
}
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