Subject: Re: [PATCH v2 3/5] ebpf: add a way to dump an eBPF program

From: Tycho Andersen <[email-masked]>
Date: Fri, 11 Sep 2015 08:44:51 -0600

On Fri, Sep 11, 2015 at 03:39:14PM +0200, Daniel Borkmann wrote:
> On 09/11/2015 02:21 AM, Tycho Andersen wrote:
> >This commit adds a way to dump eBPF programs. The initial implementation
> >doesn't support maps, and therefore only allows dumping seccomp ebpf
> >programs which themselves don't currently support maps.
> >
> >v2: don't export a prog_id for the filter
> >
> >Signed-off-by: Tycho Andersen <[email-masked]>
> >CC: Kees Cook <[email-masked]>
> >CC: Will Drewry <[email-masked]>
> >CC: Oleg Nesterov <[email-masked]>
> >CC: Andy Lutomirski <[email-masked]>
> >CC: Pavel Emelyanov <[email-masked]>
> >CC: Serge E. Hallyn <[email-masked]>
> >CC: Alexei Starovoitov <[email-masked]>
> >CC: Daniel Borkmann <[email-masked]>
> [...]
> >diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
> >index dc9b464..58ae9f4 100644
> >--- a/kernel/bpf/syscall.c
> >+++ b/kernel/bpf/syscall.c
> >@@ -586,6 +586,44 @@ free_prog:
> >  	return err;
> >  }
> >
> >+static int bpf_prog_dump(union bpf_attr *attr, union bpf_attr __user *uattr)
> >+{
> >+	int ufd = attr->prog_fd;
> >+	struct fd f = fdget(ufd);
> >+	struct bpf_prog *prog;
> >+	int ret = -EINVAL;
> >+
> >+	prog = get_prog(f);
> >+	if (IS_ERR(prog))
> >+		return PTR_ERR(prog);
> >+
> >+	/* For now, let's refuse to dump anything that isn't a seccomp program.
> >+	 * Other program types have support for maps, which our current dump
> >+	 * code doesn't support.
> >+	 */
> >+	if (prog->type != BPF_PROG_TYPE_SECCOMP)
> >+		goto out;
> 
> Yep, also when you start adding helper calls (next to map objects) you'd
> need to undo kernel pointers that the verifier sets here.

Good point, I'll add that to the comment as well.

Tycho