Re: [PATCH v2] bpf: Set register type according to is_valid_access()

On Thu, Sep 22, 2016 at 09:56:47PM +0200, Mickaël Salaün wrote:

This fix a pointer leak when an unprivileged eBPF program read a pointer
value from the context. Even if is_valid_access() returns a pointer
type, the eBPF verifier replace it with UNKNOWN_VALUE. The register
value containing an address is then allowed to leak. Moreover, this
prevented unprivileged eBPF programs to use functions with (legitimate)
pointer arguments.

This bug is not an issue for now because the only unprivileged eBPF
program allowed is of type BPF_PROG_TYPE_SOCKET_FILTER and all the types
from its context are UNKNOWN_VALUE. However, this fix is important for
future unprivileged eBPF program types which could use pointers in their
context.

Signed-off-by: Mickaël Salaün <mic@digikod.net>
Fixes: 969bf05eb3ce ("bpf: direct packet access")

Please drop 'fixes' tag and rewrite commit log.
It's not a fix.
Right now only two reg types can be seen: PTR_TO_PACKET and PTR_TO_PACKET_END.
Both are only in clsact and xdp programs which are root only.
So nothing is leaking at present.
Best case this patch is a pre-patch for some future work.