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|
package shim
import (
"encoding/gob"
"errors"
"flag"
"fmt"
"net"
"os"
"path"
"strconv"
"syscall"
"git.ophivana.moe/cat/fortify/helper"
init0 "git.ophivana.moe/cat/fortify/internal/init"
"git.ophivana.moe/cat/fortify/internal/verbose"
)
// everything beyond this point runs as target user
// proceed with caution!
func doShim(socket string) {
// re-exec
if len(os.Args) > 0 && os.Args[0] != "fortify" && path.IsAbs(os.Args[0]) {
if err := syscall.Exec(os.Args[0], []string{"fortify", "shim"}, os.Environ()); err != nil {
fmt.Println("fortify-shim: cannot re-exec self:", err)
// continue anyway
}
}
verbose.Prefix = "fortify-shim:"
// dial setup socket
var conn *net.UnixConn
if c, err := net.DialUnix("unix", nil, &net.UnixAddr{Name: socket, Net: "unix"}); err != nil {
fmt.Println("fortify-shim: cannot dial setup socket:", err)
os.Exit(1)
} else {
conn = c
}
// decode payload gob stream
var payload Payload
if err := gob.NewDecoder(conn).Decode(&payload); err != nil {
fmt.Println("fortify-shim: cannot decode shim payload:", err)
os.Exit(1)
} else {
// sharing stdout with parent
// USE WITH CAUTION
verbose.Set(payload.Verbose)
}
if payload.Bwrap == nil {
fmt.Println("fortify-shim: bwrap config not supplied")
os.Exit(1)
}
// receive wayland fd over socket
wfd := -1
if payload.WL {
if fd, err := receiveWLfd(conn); err != nil {
fmt.Println("fortify-shim: cannot receive wayland fd:", err)
os.Exit(1)
} else {
wfd = fd
}
}
// close setup socket
if err := conn.Close(); err != nil {
fmt.Println("fortify-shim: cannot close setup socket:", err)
// not fatal
}
var ic init0.Payload
// resolve argv0
ic.Argv = payload.Argv
if len(ic.Argv) > 0 {
// looked up from $PATH by parent
ic.Argv0 = payload.Exec[2]
} else {
// no argv, look up shell instead
var ok bool
if ic.Argv0, ok = os.LookupEnv("SHELL"); !ok {
fmt.Println("fortify-shim: no command was specified and $SHELL was unset")
os.Exit(1)
}
ic.Argv = []string{ic.Argv0}
}
conf := payload.Bwrap
var extraFiles []*os.File
// pass wayland fd
if wfd != -1 {
if f := os.NewFile(uintptr(wfd), "wayland"); f != nil {
ic.WL = 3 + len(extraFiles)
extraFiles = append(extraFiles, f)
}
} else {
ic.WL = -1
}
// share config pipe
if r, w, err := os.Pipe(); err != nil {
fmt.Println("fortify-shim: cannot pipe:", err)
os.Exit(1)
} else {
conf.SetEnv[init0.EnvInit] = strconv.Itoa(3 + len(extraFiles))
extraFiles = append(extraFiles, r)
verbose.Println("transmitting config to init")
go func() {
// stream config to pipe
if err = gob.NewEncoder(w).Encode(&ic); err != nil {
fmt.Println("fortify-shim: cannot transmit init config:", err)
os.Exit(1)
}
}()
}
helper.BubblewrapName = payload.Exec[1] // resolved bwrap path by parent
if b, err := helper.NewBwrap(conf, nil, payload.Exec[0], func(int, int) []string { return []string{"init"} }); err != nil {
fmt.Println("fortify-shim: malformed sandbox config:", err)
os.Exit(1)
} else {
cmd := b.Unwrap()
cmd.Stdin, cmd.Stdout, cmd.Stderr = os.Stdin, os.Stdout, os.Stderr
cmd.ExtraFiles = extraFiles
if verbose.Get() {
verbose.Println("bwrap args:", conf.Args())
}
// run and pass through exit code
if err = b.Start(); err != nil {
fmt.Println("fortify-shim: cannot start target process:", err)
os.Exit(1)
} else if err = b.Wait(); err != nil {
verbose.Println("wait:", err)
}
if b.Unwrap().ProcessState != nil {
os.Exit(b.Unwrap().ProcessState.ExitCode())
} else {
os.Exit(127)
}
}
}
func receiveWLfd(conn *net.UnixConn) (int, error) {
oob := make([]byte, syscall.CmsgSpace(4)) // single fd
if _, oobn, _, _, err := conn.ReadMsgUnix(nil, oob); err != nil {
return -1, err
} else if len(oob) != oobn {
return -1, errors.New("invalid message length")
}
var msg syscall.SocketControlMessage
if messages, err := syscall.ParseSocketControlMessage(oob); err != nil {
return -1, err
} else if len(messages) != 1 {
return -1, errors.New("unexpected message count")
} else {
msg = messages[0]
}
if fds, err := syscall.ParseUnixRights(&msg); err != nil {
return -1, err
} else if len(fds) != 1 {
return -1, errors.New("unexpected fd count")
} else {
return fds[0], nil
}
}
// Try runs shim and stops execution if FORTIFY_SHIM is set.
func Try() {
if args := flag.Args(); len(args) == 1 && args[0] == "shim" {
if s, ok := os.LookupEnv(EnvShim); ok {
doShim(s)
panic("unreachable")
}
}
}
|
