On Sep 11, 2015 9:44 AM, "Tycho Andersen" <tycho.ander...@canonical.com> wrote: > > On Fri, Sep 11, 2015 at 09:20:55AM -0700, Andy Lutomirski wrote: > > On Sep 10, 2015 5:22 PM, "Tycho Andersen" <tycho.ander...@canonical.com> > > wrote: > > > > > > This patch adds a way for a process that is "real root" to access the > > > seccomp filters of another process. The process first does a > > > PTRACE_SECCOMP_GET_FILTER_FD to get an fd with that process' seccomp > > > filter > > > attached, and then iterates on this with PTRACE_SECCOMP_NEXT_FILTER using > > > bpf(BPF_PROG_DUMP) to dump the actual program at each step. > > > > > > > > + > > > + fd = bpf_new_fd(filter->prog, O_RDONLY); > > > + if (fd > 0) > > > + atomic_inc(&filter->prog->aux->refcnt); > > > > Why isn't this folded into bpf_new_fd? > > No reason it can't be as far as I can see. I'll make the change for > the next version. > > > > + > > > + return fd; > > > +} > > > + > > > +long seccomp_next_filter(struct task_struct *child, u32 fd) > > > +{ > > > + struct seccomp_filter *cur; > > > + struct bpf_prog *prog; > > > + long ret = -ESRCH; > > > + > > > + if (!capable(CAP_SYS_ADMIN)) > > > + return -EACCES; > > > + > > > + if (child->seccomp.mode != SECCOMP_MODE_FILTER) > > > + return -EINVAL; > > > + > > > + prog = bpf_prog_get(fd); > > > + if (IS_ERR(prog)) { > > > + ret = PTR_ERR(prog); > > > + goto out; > > > + } > > > + > > > + for (cur = child->seccomp.filter; cur; cur = cur->prev) { > > > + if (cur->prog == prog) { > > > + if (!cur->prev) > > > + ret = -ENOENT; > > > + else > > > + ret = bpf_prog_set(fd, cur->prev->prog); > > > > This lets you take an fd pointing to one prog and point it elsewhere. > > I'm not sure that's a good idea. > > That's how the interface was designed (calling ptrace(NEXT_FILTER, fd) and > then doing bpf(DUMP, fd)). I suppose we could have NEXT_FILTER return > a new fd instead if that seems better to you.
It'll be slower, but it avoids a weird side effect. > > Tycho -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/