[PATCH 5.4 090/259] net: netconsole: Disable target before netpoll cleanup

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5.4-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Breno Leitao <leitao@xxxxxxxxxx>

commit 97d9fba9a812cada5484667a46e14a4c976ca330 upstream.

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@xxxxxxxxxxxxxxx
Signed-off-by: Breno Leitao <leitao@xxxxxxxxxx>
Reviewed-by: Eric Dumazet <edumazet@xxxxxxxxxx>
Link: https://patch.msgid.link/20240712143415.1141039-1-leitao@xxxxxxxxxx
Signed-off-by: Jakub Kicinski <kuba@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
 drivers/net/netconsole.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/drivers/net/netconsole.c
+++ b/drivers/net/netconsole.c
@@ -715,6 +715,7 @@ restart:
 				/* rtnl_lock already held
 				 * we might sleep in __netpoll_cleanup()
 				 */
+				nt->enabled = false;
 				spin_unlock_irqrestore(&target_list_lock, flags);
 
 				__netpoll_cleanup(&nt->np);
@@ -722,7 +723,6 @@ restart:
 				spin_lock_irqsave(&target_list_lock, flags);
 				dev_put(nt->np.dev);
 				nt->np.dev = NULL;
-				nt->enabled = false;
 				stopped = true;
 				netconsole_target_put(nt);
 				goto restart;






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