From ef0f28bc8efdc5292ceb593c9c5a646f030e0994 Mon Sep 17 00:00:00 2001
From: Phil Sutter <psutter@redhat.com>
Date: Thu, 9 Feb 2023 15:25:37 +0100
Subject: [PATCH] monitor: Sanitize startup race condition

Bugzilla: https://bugzilla.redhat.com/show_bug.cgi?id=2130721
Upstream Status: nftables commit 545edb7a8ef0a

commit 545edb7a8ef0a8acf991b1b7857fddc24d7b151a
Author: Phil Sutter <phil@nwl.cc>
Date:   Wed Sep 28 23:26:42 2022 +0200

    monitor: Sanitize startup race condition

    During startup, 'nft monitor' first fetches the current ruleset and then
    keeps this cache up to date based on received events. This is racey, as
    any ruleset changes in between the initial fetch and the socket opening
    are not recognized.

    This script demonstrates the problem:

    | #!/bin/bash
    |
    | while true; do
    |       nft flush ruleset
    |       iptables-nft -A FORWARD
    | done &
    | maniploop=$!
    |
    | trap "kill $maniploop; kill \$!; wait" EXIT
    |
    | while true; do
    |       nft monitor rules >/dev/null &
    |       sleep 0.2
    |       kill $!
    | done

    If the table add event is missed, the rule add event callback fails to
    deserialize the rule and calls abort().

    Avoid the inconvenient program exit by returning NULL from
    netlink_delinearize_rule() instead of aborting and make callers check
    the return value.

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

Signed-off-by: Phil Sutter <psutter@redhat.com>
---
 src/cache.c               | 1 +
 src/monitor.c             | 5 +++++
 src/netlink_delinearize.c | 5 ++++-
 3 files changed, 10 insertions(+), 1 deletion(-)

diff --git a/src/cache.c b/src/cache.c
index fd8df88..701aec6 100644
--- a/src/cache.c
+++ b/src/cache.c
@@ -490,6 +490,7 @@ static int list_rule_cb(struct nftnl_rule *nlr, void *data)
 
 	netlink_dump_rule(nlr, ctx);
 	rule = netlink_delinearize_rule(ctx, nlr);
+	assert(rule);
 	list_add_tail(&rule->list, &ctx->list);
 
 	return 0;
diff --git a/src/monitor.c b/src/monitor.c
index 7fa92eb..a6b30a1 100644
--- a/src/monitor.c
+++ b/src/monitor.c
@@ -551,6 +551,10 @@ static int netlink_events_rule_cb(const struct nlmsghdr *nlh, int type,
 
 	nlr = netlink_rule_alloc(nlh);
 	r = netlink_delinearize_rule(monh->ctx, nlr);
+	if (!r) {
+		fprintf(stderr, "W: Received event for an unknown table.\n");
+		goto out_free_nlr;
+	}
 	nlr_for_each_set(nlr, rule_map_decompose_cb, NULL,
 			 &monh->ctx->nft->cache);
 	cmd = netlink_msg2cmd(type, nlh->nlmsg_flags);
@@ -587,6 +591,7 @@ static int netlink_events_rule_cb(const struct nlmsghdr *nlh, int type,
 		break;
 	}
 	rule_free(r);
+out_free_nlr:
 	nftnl_rule_free(nlr);
 	return MNL_CB_OK;
 }
diff --git a/src/netlink_delinearize.c b/src/netlink_delinearize.c
index c6ad84d..1d47c74 100644
--- a/src/netlink_delinearize.c
+++ b/src/netlink_delinearize.c
@@ -3194,7 +3194,10 @@ struct rule *netlink_delinearize_rule(struct netlink_ctx *ctx,
 	pctx->rule = rule_alloc(&netlink_location, &h);
 	pctx->table = table_cache_find(&ctx->nft->cache.table_cache,
 				       h.table.name, h.family);
-	assert(pctx->table != NULL);
+	if (!pctx->table) {
+		errno = ENOENT;
+		return NULL;
+	}
 
 	pctx->rule->comment = nftnl_rule_get_comment(nlr);
 
-- 
2.39.1