netdev - [PATCH net] net: fib: avoid warn splat in flow dissector

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Date: Wed, 30 Aug 2023 13:00:37 +0200
From: Florian Westphal <fw@...len.de>
To: <netdev@...r.kernel.org>
Cc: Florian Westphal <fw@...len.de>,
	Stanislav Fomichev <sdf@...gle.com>,
	David Ahern <dsahern@...nel.org>,
	Ido Schimmel <idosch@...dia.com>
Subject: [PATCH net] net: fib: avoid warn splat in flow dissector

New skbs allocated via nf_send_reset() have skb->dev == NULL.

fib*_rules_early_flow_dissect helpers already have a 'struct net'
argument but its not passed down to the flow dissector core, which
will then WARN as it can't derive a net namespace to use:

 WARNING: CPU: 0 PID: 0 at net/core/flow_dissector.c:1016 __skb_flow_dissect+0xa91/0x1cd0
 [..]
  ip_route_me_harder+0x143/0x330
  nf_send_reset+0x17c/0x2d0 [nf_reject_ipv4]
  nft_reject_inet_eval+0xa9/0xf2 [nft_reject_inet]
  nft_do_chain+0x198/0x5d0 [nf_tables]
  nft_do_chain_inet+0xa4/0x110 [nf_tables]
  nf_hook_slow+0x41/0xc0
  ip_local_deliver+0xce/0x110
  ..

Cc: Stanislav Fomichev <sdf@...gle.com>
Cc: David Ahern <dsahern@...nel.org>
Cc: Ido Schimmel <idosch@...dia.com>
Fixes: 812fa71f0d96 ("netfilter: Dissect flow after packet mangling")
Link: https://bugzilla.kernel.org/show_bug.cgi?id=217826
Signed-off-by: Florian Westphal <fw@...len.de>
---
 include/net/ip6_fib.h | 5 ++++-
 include/net/ip_fib.h  | 5 ++++-
 2 files changed, 8 insertions(+), 2 deletions(-)

diff --git a/include/net/ip6_fib.h b/include/net/ip6_fib.h
index c9ff23cf313e..1ba9f4ddf2f6 100644
--- a/include/net/ip6_fib.h
+++ b/include/net/ip6_fib.h
@@ -642,7 +642,10 @@ static inline bool fib6_rules_early_flow_dissect(struct net *net,
 	if (!net->ipv6.fib6_rules_require_fldissect)
 		return false;
 
-	skb_flow_dissect_flow_keys(skb, flkeys, flag);
+	memset(flkeys, 0, sizeof(*flkeys));
+	__skb_flow_dissect(net, skb, &flow_keys_dissector,
+			   flkeys, NULL, 0, 0, 0, flag);
+
 	fl6->fl6_sport = flkeys->ports.src;
 	fl6->fl6_dport = flkeys->ports.dst;
 	fl6->flowi6_proto = flkeys->basic.ip_proto;
diff --git a/include/net/ip_fib.h b/include/net/ip_fib.h
index a378eff827c7..f0c13864180e 100644
--- a/include/net/ip_fib.h
+++ b/include/net/ip_fib.h
@@ -418,7 +418,10 @@ static inline bool fib4_rules_early_flow_dissect(struct net *net,
 	if (!net->ipv4.fib_rules_require_fldissect)
 		return false;
 
-	skb_flow_dissect_flow_keys(skb, flkeys, flag);
+	memset(flkeys, 0, sizeof(*flkeys));
+	__skb_flow_dissect(net, skb, &flow_keys_dissector,
+			   flkeys, NULL, 0, 0, 0, flag);
+
 	fl4->fl4_sport = flkeys->ports.src;
 	fl4->fl4_dport = flkeys->ports.dst;
 	fl4->flowi4_proto = flkeys->basic.ip_proto;
-- 
2.41.0