From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (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 082EC457E56 for ; Fri, 9 Oct 2026 07:44:12 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1791531854; cv=none; b=jt5hNYatXoS9WzfJcpbERPXASnjot+PAIOmK9EOvS3F253raCtBWomsXQ225JuLLZ/4DhNl1vNHbQH4FJPHgZlsNIC0PPkGHXDYR4vbK3vKyPOQYN6h5XegL0BXd/HrrPSxthbY8B4YjdoErRQv6ScHbVhnywn0jKrr1nCUaSNM= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1791531854; c=relaxed/simple; bh=m1WmAY5g1ebSDH4cjX37xA1Lx8rITb4V2u+6EUWh+AE=; h=From:To:Cc:Subject:Date:Message-ID:MIME-Version; b=GAoN5Ix6uADd5ipXqA/nvDr3/A3x0HjDXGii9sLDm60mZwbdJW4uZoDFNIhmu2+p4OWk251L5iZUENWpPPAUE8dd0Cz+CkeCHAgiT9mPblYv0FepwJETi4Kb/O1gaec951/O3s0ZbzUL22eNfvl4VFB0iVI8RWL7aW2FwmAbBBA= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=R44qMcgl; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="R44qMcgl" Received: by smtp.kernel.org (Postfix) with ESMTPSA id BDAC11F000FF; Fri, 9 Oct 2026 07:44:08 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1791531852; bh=7kfQmmz2VEfOe+stV4PsQ8pwfY4vcNZihIKqHxDLvkc=; h=From:To:Cc:Subject:Date; b=R44qMcglzHELOSIy23JWOybaYdrwIb30QyGGKplMGX7ih6WJreCMjmqH66ANF8+9v rj8c6j256i1bk+EusM9xkoZB8c+vHeDz5QakcAniaC0nZPB0rKRlnv8jrJs7Tr7+h7 EsDPqwFfu8Qtjt5dcIVvo0zBGb4EqEUNf8KYwL4SeFtkwQ0XWBFZjbIO5/JJfzCL5L O7acGfZSygVpdoVhWeZO2npznOzuEZzIV16kRg296xZsQHF9vKd83extvCJ8uOnO38 Zjg9NTQ+UncBrtn/LVN9k1kqhEJrSwGdgD0cIt7VEErFFg23PxcqbOS+IBa34mM0xO 3Q484rtZv8kUw== From: Eric Dumazet To: "David S . Miller" , Jakub Kicinski , Paolo Abeni Cc: Simon Horman , David Ahern , Ido Schimmel , Kuniyuki Iwashima , netdev@vger.kernel.org, Eric Dumazet , Baul Lee , Cen Zhang Subject: [PATCH net] ipv4: use RCU protection in inet_netconf_get_devconf() Date: Fri, 9 Oct 2026 09:44:05 +0200 Message-ID: <20261009074405.727999-1-edumazet@kernel.org> X-Mailer: git-send-email 2.53.0 Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit From: Eric Dumazet inet_netconf_get_devconf() runs without RTNL. It uses dev_get_by_index() and in_dev_get() to pin the device and its in_device while the reply is allocated and filled. in_dev_get() is not safe for a lockless caller. Since commit 9d40c84cf5bc ("net: devinet: Reduce refcount before grace period"), inetdev_destroy() drops the final reference before the RCU grace period. A reader can load dev->ip_ptr, then call refcount_inc() on a zero refcount after in_dev_free_rcu() has been queued, and keep using the in_device once it has been freed. None of these references are needed. An in_device is freed after an RCU grace period, ipv4_devconf is embedded in it, and inet_netconf_fill_devconf() does not sleep. Allocate the skb first, then perform the lookup and the fill under rcu_read_lock(), using dev_get_by_index_rcu() and __in_dev_get_rcu(), like inet_netconf_dump_devconf() already does. Fixes: bbcf91053bb6 ("inet: do not use RTNL in inet_netconf_get_devconf()") Reported-by: Baul Lee Closes: https://lore.kernel.org/netdev/20260815172032.79740-1-baul.lee@xbow.com/ Signed-off-by: Eric Dumazet Cc: Cen Zhang --- net/ipv4/devinet.c | 35 +++++++++++++++++------------------ 1 file changed, 17 insertions(+), 18 deletions(-) diff --git a/net/ipv4/devinet.c b/net/ipv4/devinet.c index 5b6b11c943e453742b4893f1c9bd9e70d3d37a6f..f9a361621f74b420276006b13de94926e13af18e 100644 --- a/net/ipv4/devinet.c +++ b/net/ipv4/devinet.c @@ -2379,8 +2379,8 @@ static int inet_netconf_get_devconf(struct sk_buff *in_skb, struct net *net = sock_net(in_skb->sk); struct nlattr *tb[NETCONFA_MAX + 1]; const struct ipv4_devconf *devconf; - struct in_device *in_dev = NULL; - struct net_device *dev = NULL; + struct in_device *in_dev; + struct net_device *dev; struct sk_buff *skb; int ifindex; int err; @@ -2392,7 +2392,13 @@ static int inet_netconf_get_devconf(struct sk_buff *in_skb, if (!tb[NETCONFA_IFINDEX]) return -EINVAL; + skb = nlmsg_new(inet_netconf_msgsize_devconf(NETCONFA_ALL), GFP_KERNEL); + if (!skb) + return -ENOBUFS; + ifindex = nla_get_s32(tb[NETCONFA_IFINDEX]); + + rcu_read_lock(); switch (ifindex) { case NETCONFA_IFINDEX_ALL: devconf = net->ipv4.devconf_all; @@ -2402,36 +2408,29 @@ static int inet_netconf_get_devconf(struct sk_buff *in_skb, break; default: err = -ENODEV; - dev = dev_get_by_index(net, ifindex); - if (dev) - in_dev = in_dev_get(dev); + dev = dev_get_by_index_rcu(net, ifindex); + if (!dev) + goto out_unlock; + in_dev = __in_dev_get_rcu(dev); if (!in_dev) - goto errout; + goto out_unlock; devconf = &in_dev->cnf; break; } - err = -ENOBUFS; - skb = nlmsg_new(inet_netconf_msgsize_devconf(NETCONFA_ALL), GFP_KERNEL); - if (!skb) - goto errout; - err = inet_netconf_fill_devconf(skb, ifindex, devconf, NETLINK_CB(in_skb).portid, nlh->nlmsg_seq, RTM_NEWNETCONF, 0, NETCONFA_ALL); +out_unlock: + rcu_read_unlock(); if (err < 0) { /* -EMSGSIZE implies BUG in inet_netconf_msgsize_devconf() */ WARN_ON(err == -EMSGSIZE); kfree_skb(skb); - goto errout; + return err; } - err = rtnl_unicast(skb, net, NETLINK_CB(in_skb).portid); -errout: - if (in_dev) - in_dev_put(in_dev); - dev_put(dev); - return err; + return rtnl_unicast(skb, net, NETLINK_CB(in_skb).portid); } static int inet_netconf_dump_devconf(struct sk_buff *skb, -- 2.53.0