From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id DAB2625A33A; Mon, 1 Dec 2025 11:33:22 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1764588803; cv=none; b=jNm9EywNpYaXpoDhvbHdWSPzS2Z3U5s8ra/zu502nFeaNOyQprjbMEt5FDFI6sDMbmX0L0OZ8RD+ORkBxqi7SzRg3xOS4ZXwoYnZIztIw4kXr4ed6wYQ20noXpUf5IyYo+eDnIBnpqRi6LinLmI0BXvPFPtjB4BH0fKFf06eUxw= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1764588803; c=relaxed/simple; bh=boSPu/Kq1uytmidNmBQBZ4eqSzAy40KYofzKXRLDFpw=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=XADOPViuJswGXgFzzYSvrsSFKF1ud/Rss72nmNNyED2lgQdekbU5WR2cBcrB3uAUaN55b4ny0/s/+B1XL5Jmj+dRnxz/Zx/CF5C5HlFO077iNWt2OcNpIZx1nzc++jF/fWpPiWiQsBUcsIsUlHOvJzHjx273qVWJMgANCMcEXHs= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=wns6SF4O; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="wns6SF4O" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 47EF8C4CEF1; Mon, 1 Dec 2025 11:33:22 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1764588802; bh=boSPu/Kq1uytmidNmBQBZ4eqSzAy40KYofzKXRLDFpw=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=wns6SF4OCV8NmgYxTKOxWwpHSEjO2RFQisldw40G46BfkVeryxcrKdPDtKs/Bzx6i TFH3xKDQFVwhiSpRYIHqooPvkbzZOOPg0fahsbvGnzxhFA6OvGoiYyjhceg+yC517m uAUNBax3wvj47za/MnLculVNqFnHen6VQdpQkC+g= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Jay Vosburgh , Breno Leitao , Simon Horman , Jakub Kicinski , Sasha Levin Subject: [PATCH 5.4 176/187] net: netpoll: fix incorrect refcount handling causing incorrect cleanup Date: Mon, 1 Dec 2025 12:24:44 +0100 Message-ID: <20251201112247.565140318@linuxfoundation.org> X-Mailer: git-send-email 2.52.0 In-Reply-To: <20251201112241.242614045@linuxfoundation.org> References: <20251201112241.242614045@linuxfoundation.org> User-Agent: quilt/0.69 X-stable: review X-Patchwork-Hint: ignore Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 5.4-stable review patch. If anyone has any objections, please let me know. ------------------ From: Breno Leitao [ Upstream commit 49c8d2c1f94cc2f4d1a108530d7ba52614b874c2 ] commit efa95b01da18 ("netpoll: fix use after free") incorrectly ignored the refcount and prematurely set dev->npinfo to NULL during netpoll cleanup, leading to improper behavior and memory leaks. Scenario causing lack of proper cleanup: 1) A netpoll is associated with a NIC (e.g., eth0) and netdev->npinfo is allocated, and refcnt = 1 - Keep in mind that npinfo is shared among all netpoll instances. In this case, there is just one. 2) Another netpoll is also associated with the same NIC and npinfo->refcnt += 1. - Now dev->npinfo->refcnt = 2; - There is just one npinfo associated to the netdev. 3) When the first netpolls goes to clean up: - The first cleanup succeeds and clears np->dev->npinfo, ignoring refcnt. - It basically calls `RCU_INIT_POINTER(np->dev->npinfo, NULL);` - Set dev->npinfo = NULL, without proper cleanup - No ->ndo_netpoll_cleanup() is either called 4) Now the second target tries to clean up - The second cleanup fails because np->dev->npinfo is already NULL. * In this case, ops->ndo_netpoll_cleanup() was never called, and the skb pool is not cleaned as well (for the second netpoll instance) - This leaks npinfo and skbpool skbs, which is clearly reported by kmemleak. Revert commit efa95b01da18 ("netpoll: fix use after free") and adds clarifying comments emphasizing that npinfo cleanup should only happen once the refcount reaches zero, ensuring stable and correct netpoll behavior. Cc: # 3.17.x Cc: Jay Vosburgh Fixes: efa95b01da18 ("netpoll: fix use after free") Signed-off-by: Breno Leitao Reviewed-by: Simon Horman Link: https://patch.msgid.link/20251107-netconsole_torture-v10-1-749227b55f63@debian.org Signed-off-by: Jakub Kicinski [ Adjust context ] Signed-off-by: Sasha Levin Signed-off-by: Greg Kroah-Hartman --- net/core/netpoll.c | 7 +++++-- 1 file changed, 5 insertions(+), 2 deletions(-) --- a/net/core/netpoll.c +++ b/net/core/netpoll.c @@ -858,6 +858,10 @@ void __netpoll_cleanup(struct netpoll *n synchronize_srcu(&netpoll_srcu); + /* At this point, there is a single npinfo instance per netdevice, and + * its refcnt tracks how many netpoll structures are linked to it. We + * only perform npinfo cleanup when the refcnt decrements to zero. + */ if (refcount_dec_and_test(&npinfo->refcnt)) { const struct net_device_ops *ops; @@ -867,8 +871,7 @@ void __netpoll_cleanup(struct netpoll *n RCU_INIT_POINTER(np->dev->npinfo, NULL); call_rcu(&npinfo->rcu, rcu_cleanup_netpoll_info); - } else - RCU_INIT_POINTER(np->dev->npinfo, NULL); + } } EXPORT_SYMBOL_GPL(__netpoll_cleanup);