netdev - [PATCH net-next] net: Prevent use after free in netif_napi_set_irq

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Message-ID: <5a9c53a4-5487-4b8c-9ffa-d8e5343aaaaf@stanley.mountain>
Date: Mon, 3 Mar 2025 15:02:12 +0300
From: Dan Carpenter <dan.carpenter@...aro.org>
To: Ahmed Zaki <ahmed.zaki@...el.com>
Cc: "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>,
	Kuniyuki Iwashima <kuniyu@...zon.com>,
	Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
	Alexander Lobakin <aleksander.lobakin@...el.com>,
	netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
	kernel-janitors@...r.kernel.org
Subject: [PATCH net-next] net: Prevent use after free in
 netif_napi_set_irq_locked()

The cpu_rmap_put() will call kfree() when the last reference is dropped
so it could result in a use after free when we dereference the same
pointer the next line.  Move the cpu_rmap_put() after the dereference.

Fixes: bd7c00605ee0 ("net: move aRFS rmap management and CPU affinity to core")
Signed-off-by: Dan Carpenter <dan.carpenter@...aro.org>
---
 net/core/dev.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/core/dev.c b/net/core/dev.c
index 9189c4a048d7..c102349e04ee 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -7072,8 +7072,8 @@ void netif_napi_set_irq_locked(struct napi_struct *napi, int irq)
 put_rmap:
 #ifdef CONFIG_RFS_ACCEL
 	if (napi->dev->rx_cpu_rmap_auto) {
-		cpu_rmap_put(napi->dev->rx_cpu_rmap);
 		napi->dev->rx_cpu_rmap->obj[napi->napi_rmap_idx] = NULL;
+		cpu_rmap_put(napi->dev->rx_cpu_rmap);
 		napi->napi_rmap_idx = -1;
 	}
 #endif
-- 
2.47.2