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 21E1C30E0DC; Fri, 21 Nov 2025 13:33:56 +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=1763732037; cv=none; b=Bzzo4KxgB1jbsKD7/8j6zPIEYItk/gnTopAADtLSPYRnHtkeQp1G5E8s7ltWaWyoQRoLpm2J/b3i9/0eYtDzVbKncZnN+KJ7Rblvv1NRR5PUON4zifgjHqhQo8BJ1aUt3nH9nZn2tXNmui6a7KyMfKxztC/U7oWxinpnzn85ArI= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1763732037; c=relaxed/simple; bh=j2NQzai8TY1kyIDFvf8v0VvUJq0ea/b7LuAGFKC5ogU=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=kYTxDJQg0XtGhCGiTuYBXblHRop5AbBuFafCokorc4uii6v3ncMJvATZ4IKcR/yZxI/Ju9HVu6dbEn7sTpcOux1hGtASKQZnn35CKvuhOM2T+NtHznry2m3fVvCeqOanrxrfluuTAi6QHHfaHGL2BLY1pNl6xA1vYwAk5msptDo= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=mkKmIeIR; 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="mkKmIeIR" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 5F77FC4CEF1; Fri, 21 Nov 2025 13:33:56 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1763732036; bh=j2NQzai8TY1kyIDFvf8v0VvUJq0ea/b7LuAGFKC5ogU=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=mkKmIeIRf7XKuLDFHe5JZbemyzqrQdUQewVxL3UynQydQwhaMIGV+HWIj6LDKqs7Z tGtHJDoqxGmwwAQaBQPwAF843awrgOhh6yPHq4lENzjSU6D9ZOqQfWrbFxxjj1iKWe /GDJ1IGoR9UJbgKy/gW6hJMwcHDMMNyjjacG2qls= 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 6.12 168/185] net: netpoll: fix incorrect refcount handling causing incorrect cleanup Date: Fri, 21 Nov 2025 14:13:15 +0100 Message-ID: <20251121130149.943860664@linuxfoundation.org> X-Mailer: git-send-email 2.52.0 In-Reply-To: <20251121130143.857798067@linuxfoundation.org> References: <20251121130143.857798067@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 6.12-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 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 @@ -841,6 +841,10 @@ void __netpoll_cleanup(struct netpoll *n if (!npinfo) return; + /* 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; @@ -850,8 +854,7 @@ 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); + } skb_pool_flush(np); }