netdev - [PATCH net 2/2] netpoll: Use rcu_access_pointer() in netpoll_poll

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-Id: <20241118-netpoll_rcu-v1-2-a1888dcb4a02@debian.org>
Date: Mon, 18 Nov 2024 03:15:18 -0800
From: Breno Leitao <leitao@...ian.org>
To: "David S. Miller" <davem@...emloft.net>, 
 Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>, 
 Paolo Abeni <pabeni@...hat.com>, Simon Horman <horms@...nel.org>, 
 Herbert Xu <herbert@...dor.apana.org.au>, 
 Stephen Hemminger <stephen@...workplumber.org>
Cc: netdev@...r.kernel.org, linux-kernel@...r.kernel.org, 
 Breno Leitao <leitao@...ian.org>, paulmck@...nel.org
Subject: [PATCH net 2/2] netpoll: Use rcu_access_pointer() in
 netpoll_poll_lock

The ndev->npinfo pointer in netpoll_poll_lock() is RCU-protected but is
being accessed directly for a NULL check. While no RCU read lock is held
in this context, we should still use proper RCU primitives for
consistency and correctness.

Replace the direct NULL check with rcu_access_pointer(), which is the
appropriate primitive when only checking for NULL without dereferencing
the pointer. This function provides the necessary ordering guarantees
without requiring RCU read-side protection.

Signed-off-by: Breno Leitao <leitao@...ian.org>
Fixes: bea3348eef27 ("[NET]: Make NAPI polling independent of struct net_device objects.")
---
 include/linux/netpoll.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/include/linux/netpoll.h b/include/linux/netpoll.h
index cd4e28db0cbd77572a579aff2067b5864d1a904a..959a4daacea1f2f76536e309d198bc14407942a4 100644
--- a/include/linux/netpoll.h
+++ b/include/linux/netpoll.h
@@ -72,7 +72,7 @@ static inline void *netpoll_poll_lock(struct napi_struct *napi)
 {
 	struct net_device *dev = napi->dev;

-	if (dev && dev->npinfo) {
+	if (dev && rcu_access_pointer(dev->npinfo)) {
 		int owner = smp_processor_id();

 		while (cmpxchg(&napi->poll_owner, -1, owner) != -1)

-- 
2.43.5