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|
package main
import (
"errors"
"os"
"path"
"strconv"
"syscall"
init0 "git.gensokyo.uk/security/fortify/cmd/finit/ipc"
shim "git.gensokyo.uk/security/fortify/cmd/fshim/ipc"
"git.gensokyo.uk/security/fortify/fst"
"git.gensokyo.uk/security/fortify/helper"
"git.gensokyo.uk/security/fortify/internal"
"git.gensokyo.uk/security/fortify/internal/fmsg"
"git.gensokyo.uk/security/fortify/internal/proc"
)
// everything beyond this point runs as unconstrained target user
// proceed with caution!
func main() {
// sharing stdout with fortify
// USE WITH CAUTION
fmsg.SetPrefix("shim")
// setting this prevents ptrace
if err := internal.PR_SET_DUMPABLE__SUID_DUMP_DISABLE(); err != nil {
fmsg.Fatalf("cannot set SUID_DUMP_DISABLE: %s", err)
panic("unreachable")
}
// re-exec
if len(os.Args) > 0 && (os.Args[0] != "fshim" || len(os.Args) != 1) && path.IsAbs(os.Args[0]) {
if err := syscall.Exec(os.Args[0], []string{"fshim"}, os.Environ()); err != nil {
fmsg.Println("cannot re-exec self:", err)
// continue anyway
}
}
// check path to finit
var finitPath string
if p, ok := internal.Path(internal.Finit); !ok {
fmsg.Fatal("invalid finit path, this copy of fshim is not compiled correctly")
} else {
finitPath = p
}
// receive setup payload
var (
payload shim.Payload
closeSetup func() error
)
if f, err := proc.Receive(shim.Env, &payload); err != nil {
if errors.Is(err, proc.ErrInvalid) {
fmsg.Fatal("invalid config descriptor")
}
if errors.Is(err, proc.ErrNotSet) {
fmsg.Fatal("FORTIFY_SHIM not set")
}
fmsg.Fatalf("cannot decode shim setup payload: %v", err)
panic("unreachable")
} else {
fmsg.SetVerbose(payload.Verbose)
closeSetup = f
}
if payload.Bwrap == nil {
fmsg.Fatal("bwrap config not supplied")
}
// restore bwrap sync fd
if payload.Sync != nil {
payload.Bwrap.SetSync(os.NewFile(*payload.Sync, "sync"))
}
// close setup socket
if err := closeSetup(); err != nil {
fmsg.Println("cannot close setup pipe:", 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[1]
} else {
// no argv, look up shell instead
var ok bool
if payload.Bwrap.SetEnv == nil {
fmsg.Fatal("no command was specified and environment is unset")
}
if ic.Argv0, ok = payload.Bwrap.SetEnv["SHELL"]; !ok {
fmsg.Fatal("no command was specified and $SHELL was unset")
}
ic.Argv = []string{ic.Argv0}
}
conf := payload.Bwrap
var extraFiles []*os.File
// serve setup payload
if fd, encoder, err := proc.Setup(&extraFiles); err != nil {
fmsg.Fatalf("cannot pipe: %v", err)
} else {
conf.SetEnv[init0.Env] = strconv.Itoa(fd)
go func() {
fmsg.VPrintln("transmitting config to init")
if err = encoder.Encode(&ic); err != nil {
fmsg.Fatalf("cannot transmit init config: %v", err)
}
}()
}
// bind finit inside sandbox
finitInnerPath := path.Join(fst.Tmp, "sbin", "init")
conf.Bind(finitPath, finitInnerPath)
helper.BubblewrapName = payload.Exec[0] // resolved bwrap path by parent
if b, err := helper.NewBwrap(conf, nil, finitInnerPath,
func(int, int) []string { return make([]string, 0) }); err != nil {
fmsg.Fatalf("malformed sandbox config: %v", err)
} else {
cmd := b.Unwrap()
cmd.Stdin, cmd.Stdout, cmd.Stderr = os.Stdin, os.Stdout, os.Stderr
cmd.ExtraFiles = extraFiles
if fmsg.Verbose() {
fmsg.VPrintln("bwrap args:", conf.Args())
}
// run and pass through exit code
if err = b.Start(); err != nil {
fmsg.Fatalf("cannot start target process: %v", err)
} else if err = b.Wait(); err != nil {
fmsg.VPrintln("wait:", err)
}
if b.Unwrap().ProcessState != nil {
fmsg.Exit(b.Unwrap().ProcessState.ExitCode())
} else {
fmsg.Exit(127)
}
}
}
|
