linux-kernel - [PATCH net v2] net: netconsole: Disable target before netpoll cleanup

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Message-ID: <20240712143415.1141039-1-leitao@debian.org>
Date: Fri, 12 Jul 2024 07:34:15 -0700
From: Breno Leitao <leitao@...ian.org>
To: davem@...emloft.net,
	edumazet@...gle.com,
	pabeni@...hat.com,
	Jakub Kicinski <kuba@...nel.org>,
	Bruno Prémont <bonbons@...ux-vserver.org>,
	Matt Mackall <mpm@...enic.com>
Cc: thepacketgeek@...il.com,
	riel@...riel.com,
	horms@...nel.org,
	netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	stable@...r.kernel.org
Subject: [PATCH net v2] net: netconsole: Disable target before netpoll cleanup

Currently, netconsole cleans up the netpoll structure before disabling
the target. This approach can lead to race conditions, as message
senders (write_ext_msg() and write_msg()) check if the target is
enabled before using netpoll. The sender can validate that the target is
enabled, but, the netpoll might be de-allocated already, causing
undesired behaviours.

This patch reverses the order of operations:
1. Disable the target
2. Clean up the netpoll structure

This change eliminates the potential race condition, ensuring that
no messages are sent through a partially cleaned-up netpoll structure.

Fixes: 2382b15bcc39 ("netconsole: take care of NETDEV_UNREGISTER event")
Cc: stable@...r.kernel.org
Signed-off-by: Breno Leitao <leitao@...ian.org>
---
Changelog:

v2:
 * Targeting "net" instead of "net-dev" (Jakub)

v1:
 * https://lore.kernel.org/all/20240709144403.544099-4-leitao@debian.org/

 drivers/net/netconsole.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/net/netconsole.c b/drivers/net/netconsole.c
index d7070dd4fe73..aa66c923790f 100644
--- a/drivers/net/netconsole.c
+++ b/drivers/net/netconsole.c
@@ -974,6 +974,7 @@ static int netconsole_netdev_event(struct notifier_block *this,
 				/* rtnl_lock already held
 				 * we might sleep in __netpoll_cleanup()
 				 */
+				nt->enabled = false;
 				spin_unlock_irqrestore(&target_list_lock, flags);
 
 				__netpoll_cleanup(&nt->np);
@@ -981,7 +982,6 @@ static int netconsole_netdev_event(struct notifier_block *this,
 				spin_lock_irqsave(&target_list_lock, flags);
 				netdev_put(nt->np.dev, &nt->np.dev_tracker);
 				nt->np.dev = NULL;
-				nt->enabled = false;
 				stopped = true;
 				netconsole_target_put(nt);
 				goto restart;
-- 
2.43.0