From 64f34f34acedad6cce70f2dd91c82a814d4ffe34 Mon Sep 17 00:00:00 2001

From: Phil Sutter <psutter@redhat.com>

Date: Wed, 19 May 2021 18:03:43 +0200

Subject: [PATCH] src: Support odd-sized payload matches

Bugzilla: https://bugzilla.redhat.com/show_bug.cgi?id=1934926

Upstream Status: nftables commit 8a927c56d83ed

commit 8a927c56d83ed0f78785011bd92a53edc25a0ca0

Author: Phil Sutter <phil@nwl.cc>

Date:   Tue Oct 27 17:05:25 2020 +0100

    src: Support odd-sized payload matches

    When expanding a payload match, don't disregard oversized templates at

    the right offset. A more flexible user may extract less bytes from the

    packet if only parts of a field are interesting, e.g. only the prefix of

    source/destination address. Support that by using the template, but fix

    the length. Later when creating a relational expression for it, detect

    the unusually small payload expression length and turn the RHS value

    into a prefix expression.

    Signed-off-by: Phil Sutter <phil@nwl.cc>

---

 src/netlink_delinearize.c | 6 ++++++

 src/payload.c             | 5 +++++

 2 files changed, 11 insertions(+)

diff --git a/src/netlink_delinearize.c b/src/netlink_delinearize.c

index 88dbd5a..8bdee12 100644

--- a/src/netlink_delinearize.c

+++ b/src/netlink_delinearize.c

@@ -1577,6 +1577,12 @@ static void payload_match_expand(struct rule_pp_ctx *ctx,

 		tmp = constant_expr_splice(right, left->len);

 		expr_set_type(tmp, left->dtype, left->byteorder);

+		if (left->payload.tmpl && (left->len < left->payload.tmpl->len)) {

+			mpz_lshift_ui(tmp->value, left->payload.tmpl->len - left->len);

+			tmp->len = left->payload.tmpl->len;

+			tmp = prefix_expr_alloc(&tmp->location, tmp, left->len);

+		}

+

 		nexpr = relational_expr_alloc(&expr->location, expr->op,

 					      left, tmp);

 		if (expr->op == OP_EQ)

diff --git a/src/payload.c b/src/payload.c

index 3576400..45280ef 100644

--- a/src/payload.c

+++ b/src/payload.c

@@ -746,6 +746,11 @@ void payload_expr_expand(struct list_head *list, struct expr *expr,

 			expr->payload.offset += tmpl->len;

 			if (expr->len == 0)

 				return;

+		} else if (expr->len > 0) {

+			new = payload_expr_alloc(&expr->location, desc, i);

+			new->len = expr->len;

+			list_add_tail(&new->list, list);

+			return;

 		} else

 			break;

 	}

-- 

1.8.3.1