Re: git: 3a1f834b5228 - main - pf: Add code to enable filtering for locally delivered packets

[Matteo Riondato]

On 2023-06-20 at 11:57 EDT, Matteo Riondato <mat...@freebsd.org> wrote:

On 2023-06-20 at 10:35 EDT, Doug Rabson <d...@freebsd.org> wrote:

The branch main has been updated by dfr:

URL: 
https://cgit.FreeBSD.org/src/commit/?id=3a1f834b5228986a7c14fd60da13cf2700e80996

commit 3a1f834b5228986a7c14fd60da13cf2700e80996
Author:     Doug Rabson <d...@freebsd.org>
AuthorDate: 2023-06-20 13:01:58 +0000
Commit:     Doug Rabson <d...@freebsd.org>
CommitDate: 2023-06-20 14:34:01 +0000

  pf: Add code to enable filtering for locally delivered packets



          sysctl net.pf.filter_local=1
          service pf restart

  PR:             268717
  Reviewed-by:    kp
  MFC-after:      2 weeks
  Differential Revision: https://reviews.freebsd.org/D40373
---
UPDATING                                     | 12 ++++++++++++
sys/netpfil/pf/pf_ioctl.c                    | 20 ++++++++++++++++++++
tests/sys/netpfil/common/utils.subr          |  3 +--
tests/sys/netpfil/pf/fragmentation_compat.sh |  3 ++-
tests/sys/netpfil/pf/fragmentation_pass.sh   |  3 ++-

tests/sys/netpfil/pf/map_e.sh                |  3 ++-
tests/sys/netpfil/pf/pass_block.sh           |  3 ++-
tests/sys/netpfil/pf/pfsync.sh               |  1 +
tests/sys/netpfil/pf/route_to.sh             |  3 ++-
tests/sys/netpfil/pf/set_skip.sh             |  2 +-
tests/sys/netpfil/pf/table.sh                |  6 ++++--
12 files changed, 65 insertions(+), 18 deletions(-)

diff --git a/UPDATING b/UPDATING
index 1980411c1853..f4e13d97006d 100644
--- a/UPDATING
+++ b/UPDATING
@@ -27,6 +27,18 @@ NOTE TO PEOPLE WHO THINK THAT FreeBSD 14.x IS SLOW:

        at runtime, run "ln -s 'abort:false,junk:false' /etc/malloc.conf".)

+20230619:
+       To enable pf rdr rules for connections initiated from the host, pf
+       filter rules can be optionally enabled for packets delivered
+       locally. This can change the behavior of rules which match packets
+       delivered to lo0. To enable this feature:
+
+               sysctl net.pf.filter_local=1
+               service pf restart

This is disabled by default since it potentially changes the behavior of existing filter rule sets. To enable this extra filter for packets being delivered locally, use: tests/sys/netpfil/pf/killstate.sh | 24 ++++++++++++++++-------- world, or to merely disable the most expensive debugging functionality

It seems a bit weird to suggest an action that is not permanent (does not survive reboot). See proposed rewording below.

+
+       When enabled, its best to ensure that packets delivered locally are not

s/its/it is/

+       filtered, e.g. by adding a 'skip on lo' rule.

Perhaps a better phrasing (assuming I understand the feature) would be:

TBH, I find the phrasing a bit confusing: "to enable pf rdr rules for connections …, pf filter rules can *optionally* be enabled for packets delivered locally". That "optionally" makes it sound as if it is not *required* to enable pf filter rules for packets delivered locally in order to enable pf rdr rules for connections etc etc., but, given this change, I assume it is. "The new sysctl net.pf.filter_local controls whether PF filter rules are enabled for packets originating from localhost and delivered locally. This feature can be useful for, e.g., enabling rdr rules for connections initiated from localhost and redirected to a different port on localhost. Setting the sysctl to 1 may change the behavior of rules which match packets delivered to lo0, so it may be necessary to add enable the "skip on lo" option." Note that "skip on" is not a rule, even if it is translated to a pair of rules: it's part of the options, and requires "set" before it, per pf.conf(5). Also, I'm assuming (and mention in the rewording) we are talking about rdr rules for port remapping, not rdr rules that redirect to other destinations, but please confirm or adjust. More generally, this new feature should likely also be documented somewhere else (pf(4) ? pfctl(8)? pf.conf(5)?). But apart from the above, I'm a little puzzled: does it mean that until now (and continuing to do so, unless one sets the sysctl to 1), packets originating locally and destined locally were not filtered by pf? I.e., that filtering rules on lo0 had no effect on incoming traffic from localhost?

Hi Doug and Kristof,





Thanks,
Matteo

A ping about what I said below, as I think there is a need to better document this sysctl. Additionally, I'm also a little worried about the name of the sysctl, which seems extremely generic, while its use may be much more specific. If the name could be made more specific, that should probably be done before 14 is branched.

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