bpftool: Don't crash on missing xlated program instructions

BugLink: https://bugs.launchpad.net/bugs/1867677

commit d95f1e8 upstream.

Turns out the xlated program instructions can also be missing if
kptr_restrict sysctl is set. This means that the previous fix to check the
jited_prog_insns pointer was insufficient; add another check of the
xlated_prog_insns pointer as well.

Fixes: 5b79bcd ("bpftool: Don't crash on missing jited insns or ksyms")
Fixes: cae73f2 ("bpftool: use bpf_program__get_prog_info_linear() in prog.c:do_dump()")
Signed-off-by: Toke Høiland-Jørgensen <toke@redhat.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Reviewed-by: Quentin Monnet <quentin@isovalent.com>
Link: https://lore.kernel.org/bpf/20200206102906.112551-1-toke@redhat.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Kamal Mostafa <kamal@canonical.com>
Signed-off-by: Khalid Elmously <khalid.elmously@canonical.com>

tools/bpf/bpftool/prog.c

@@ -500,7 +500,7 @@ static int do_dump(int argc, char **argv)
  buf = (unsigned char *)(info->jited_prog_insns);
  member_len = info->jited_prog_len;
  } else { /* DUMP_XLATED */
- if (info->xlated_prog_len == 0) {
+ if (info->xlated_prog_len == 0 || !info->xlated_prog_insns) {
  p_err("error retrieving insn dump: kernel.kptr_restrict set?");
  goto err_free;
  }