openwrt/target/linux/generic/backport-6.6/780-19-v6.10-net-annotate-writes-on-dev-mtu-from-ndo_change_mtu.patch

From 1eb2cded45b35816085c1f962933c187d970f9dc Mon Sep 17 00:00:00 2001
From: Eric Dumazet <edumazet@google.com>
Date: Mon, 6 May 2024 10:28:12 +0000
Subject: [PATCH] net: annotate writes on dev->mtu from ndo_change_mtu()

Simon reported that ndo_change_mtu() methods were never
updated to use WRITE_ONCE(dev->mtu, new_mtu) as hinted
in commit 501a90c94510 ("inet: protect against too small
mtu values.")

We read dev->mtu without holding RTNL in many places,
with READ_ONCE() annotations.

It is time to take care of ndo_change_mtu() methods
to use corresponding WRITE_ONCE()

Signed-off-by: Eric Dumazet <edumazet@google.com>
Reported-by: Simon Horman <horms@kernel.org>
Closes: https://lore.kernel.org/netdev/20240505144608.GB67882@kernel.org/
Reviewed-by: Jacob Keller <jacob.e.keller@intel.com>
Reviewed-by: Sabrina Dubroca <sd@queasysnail.net>
Reviewed-by: Simon Horman <horms@kernel.org>
Acked-by: Shannon Nelson <shannon.nelson@amd.com>
Link: https://lore.kernel.org/r/20240506102812.3025432-1-edumazet@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
---
 drivers/net/ethernet/realtek/8139cp.c     | 4 ++--
 drivers/net/ethernet/realtek/r8169_main.c | 2 +-
 2 files changed, 3 insertions(+), 3 deletions(-)

--- a/drivers/net/ethernet/realtek/8139cp.c
+++ b/drivers/net/ethernet/realtek/8139cp.c
@@ -1277,14 +1277,14 @@ static int cp_change_mtu(struct net_devi
 
 	/* if network interface not up, no need for complexity */
 	if (!netif_running(dev)) {
-		dev->mtu = new_mtu;
+		WRITE_ONCE(dev->mtu, new_mtu);
 		cp_set_rxbufsize(cp);	/* set new rx buf size */
 		return 0;
 	}
 
 	/* network IS up, close it, reset MTU, and come up again. */
 	cp_close(dev);
-	dev->mtu = new_mtu;
+	WRITE_ONCE(dev->mtu, new_mtu);
 	cp_set_rxbufsize(cp);
 	return cp_open(dev);
 }
--- a/drivers/net/ethernet/realtek/r8169_main.c
+++ b/drivers/net/ethernet/realtek/r8169_main.c
@@ -3952,7 +3952,7 @@ static int rtl8169_change_mtu(struct net
 {
 	struct rtl8169_private *tp = netdev_priv(dev);
 
-	dev->mtu = new_mtu;
+	WRITE_ONCE(dev->mtu, new_mtu);
 	netdev_update_features(dev);
 	rtl_jumbo_config(tp);
 	rtl_set_eee_txidle_timer(tp);