Commit a9ab02ed authored by Breno Leitao's avatar Breno Leitao Committed by Jakub Kicinski
Browse files

netpoll: Use rtnl_dereference() for npinfo pointer access 

In the __netpoll_setup() function, when accessing the device's npinfo
pointer, replace rcu_access_pointer() with rtnl_dereference(). This
change is more appropriate, as suggested by Herbert Xu[1].

The function is called with the RTNL mutex held, and the pointer is
being dereferenced later, so, dereference earlier and just reuse the
pointer for the if/else.

The replacement ensures correct pointer access while maintaining
the existing locking and RCU semantics of the netpoll subsystem.

Link: https://lore.kernel.org/lkml/Zz1cKZYt1e7elibV@gondor.apana.org.au/

 [1]
Suggested-by: default avatarHerbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: default avatarBreno Leitao <leitao@debian.org>
Reviewed-by: default avatarJacob Keller <jacob.e.keller@intel.com>
Acked-by: default avatarHerbert Xu <herbert@gondor.apana.org.au>
Link: https://patch.msgid.link/20241202-netpoll_rcu_herbet_fix-v2-1-2b9d58edc76a@debian.org


Signed-off-by: default avatarJakub Kicinski <kuba@kernel.org>
parent bb18265c

net/core/netpoll.c

+2 −2
Original line number Diff line number Diff line
@@ -634,7 +634,8 @@ int __netpoll_setup(struct netpoll *np, struct net_device *ndev) 
		goto out;

	}



	if (!rcu_access_pointer(ndev->npinfo)) {

	npinfo = rtnl_dereference(ndev->npinfo);

	if (!npinfo) {

		npinfo = kmalloc(sizeof(*npinfo), GFP_KERNEL);

		if (!npinfo) {

			err = -ENOMEM;
@@ -654,7 +655,6 @@ int __netpoll_setup(struct netpoll *np, struct net_device *ndev) 
				goto free_npinfo;

		}

	} else {

		npinfo = rtnl_dereference(ndev->npinfo);

		refcount_inc(&npinfo->refcnt);

	}