On Wed, Oct 19, 2016 at 11:52:50AM -0500, Eric W. Biederman wrote: > Andy Lutomirski <luto@xxxxxxxxxxxxxx> writes: > > Simply ptrace yourself, exec the > > program, and then dump the program out. A program that really wants > > to be unreadable should have a stub: the stub is setuid and readable, > > but all the stub does is to exec the real program, and the real > > program should have mode 0500 or similar. > > > > ISTM the "right" check would be to enforce that the program's new > > creds can read the program, but that will break backwards > > compatibility. > > Last I looked I had the impression that exec of a setuid program kills > the ptrace. > > If we are talking about a exec of a simple unreadable executable (aka > something that sets undumpable but is not setuid or setgid). Then I > agree it should break the ptrace as well and since those programs are as > rare as hens teeth I don't see any problem with changing the ptrace behavior > in that case. Nope. check_unsafe_exec() sets LSM_UNSAFE_* flags in bprm->unsafe, and then the flags are checked by the LSMs and cap_bprm_set_creds() in commoncap.c. cap_bprm_set_creds() just degrades the execution to a non-setuid-ish one, and e.g. ptracers stay attached. Same thing happens if the fs struct is shared with another process or if NO_NEW_PRIVS is active. (Actually, it's still a bit like normal setuid execution: IIRC AT_SECURE stays active, and the resulting process still won't be dumpable, so it's not possible for a *new* ptracer to attach afterwards. But this is just from memory, I'm not entirely sure.) -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>