On Fri, Sep 11, 2015 at 01:47:38PM +0200, Daniel Borkmann wrote:

On 09/11/2015 02:21 AM, Tycho Andersen wrote:

quoted

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.

Signed-off-by: Tycho Andersen <redacted>
CC: Kees Cook <redacted>
CC: Will Drewry <redacted>
CC: Oleg Nesterov <redacted>
CC: Andy Lutomirski <redacted>
CC: Pavel Emelyanov <redacted>
CC: Serge E. Hallyn <serge.hallyn-GeWIH/nMZzLQT0dZR+AlfA@public.gmane.org>
CC: Alexei Starovoitov <redacted>
CC: Daniel Borkmann <redacted>

[...]

quoted

diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
index 58ae9f4..ac3ed1c 100644
--- a/kernel/bpf/syscall.c
+++ b/kernel/bpf/syscall.c

@@ -506,6 +506,30 @@ struct bpf_prog *bpf_prog_get(u32 ufd)
 }
 EXPORT_SYMBOL_GPL(bpf_prog_get);

+int bpf_prog_set(u32 ufd, struct bpf_prog *new)
+{
+	struct fd f;
+	struct bpf_prog *prog;
+
+	f = fdget(ufd);
+
+	prog = get_prog(f);
+	if (!IS_ERR(prog) && prog)
+		bpf_prog_put(prog);
+
+	atomic_inc(&new->aux->refcnt);
+	f.file->private_data = new;
+	fdput(f);
+	return 0;

So in case get_prog() fails, and for example f.file is infact NULL,
you assign the bpf prog then to ERR_PTR(-EBADF)'s private_data? :(

Thanks, I will fix for the next version.

quoted

+}
+EXPORT_SYMBOL_GPL(bpf_prog_set);
+
+int bpf_new_fd(struct bpf_prog *prog, int flags)
+{
+	return anon_inode_getfd("bpf-prog", &bpf_prog_fops, prog, flags);
+}
+EXPORT_SYMBOL_GPL(bpf_new_fd);

Any reason why these two need to be exported for modules? Which
modules are using them?

I think modules should probably not mess with this.

No reason, I suppose. I was just exporting because bpf_prog_get is;
I'll drop it for the next version.

If you already name it generic, it would also be good if bpf_new_fd()
is used in case of maps that call anon_inode_getfd(), too.

I needed to call bpf_new_fd from kernel/seccomp.c, which it seems
shouldn't be able to reference bpf_prog_fops, which is why I added the
little "proxy". If we change the api to something like,

bpf_new_fd("bpf-map", &bpf_map_fops, map);
bpf_new_fd("bpf-prog", &bpf_prog_fops, prog);

I'd need access to bpf_prog_fops again. What about changing the name
to bpf_new_prog_fd?

Tycho