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 B3F7B51A720; Wed, 30 Sep 2026 17:09:06 +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=1790788147; cv=none; b=jeRvAf3VA5znJvOFfeqj177hj32V12h5p810RvICVXXw7UDNZqE5C/rABXS28EFdnZPI2B9B/ITBwCYiR6i7+5v7ukpZQzXt43QY8wh9lqEIplN6bwYcHmG737uIAACliEGVFdzCf/7iltbpW+dYm4b8Z65U4jbYntE3/b6Xt/0= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1790788147; c=relaxed/simple; bh=xyn1eIOQFpKSR7aFcl2yGqCC6XAep5bhQ6g0Ksb/gXY=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=K4dfHNCGw1Ptqc0Fx3Wt6XFOd50Z9UZl2MybDdnHeBiad76q1W05RbJI07UuAK0j+ROfH1FmNBj9orV0Z3g62Zg+hcHw4kt+yOrxwlX/sI49Tya19L/sSQWZhC9jSlSL4MJED55qv9bQrMlziaXNmsZOkopikVM8NIrq//LYZVc= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=dg7AppsO; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="dg7AppsO" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 1CAD31F000FF; Wed, 30 Sep 2026 17:09:05 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linuxfoundation.org; s=korg; t=1790788146; bh=egZJmGEIzm1zkxkznED+GyZ5alXxz26gnbS1urjF7P4=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=dg7AppsO5GCB9fbqm7zaBjYZKXlw3NIVphNBz7HY3UgkPPmHv0YT6jZK+/tqpZBDm JluGlzXg3Lh6BXHfYZ7+WYNLmvrMng9XgNHiS5vGDmolI7yTI4egzV/Tacn3P1l40S PVcgZbJcOoRPUlJlOFfZISaWONbK225jjpNRT8j4= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Kuniyuki Iwashima , Eric Dumazet , Jakub Kicinski , Sasha Levin Subject: [PATCH 6.12 015/877] ipv6: mcast: Dont hold RTNL for IPV6_ADD_MEMBERSHIP and MCAST_JOIN_GROUP. Date: Wed, 30 Sep 2026 17:15:26 +0200 Message-ID: <20260930152415.073963410@linuxfoundation.org> X-Mailer: git-send-email 2.55.0 In-Reply-To: <20260930152414.738996857@linuxfoundation.org> References: <20260930152414.738996857@linuxfoundation.org> User-Agent: quilt/0.69 X-stable: review X-Patchwork-Hint: ignore Precedence: bulk X-Mailing-List: patches@lists.linux.dev 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: Kuniyuki Iwashima [ Upstream commit 1767bb2d47b715a106287a8f963d9ec6cbab4e69 ] In __ipv6_sock_mc_join(), per-socket mld data is protected by lock_sock(), and only __dev_get_by_index() requires RTNL. Let's use dev_get_by_index() and drop RTNL for IPV6_ADD_MEMBERSHIP and MCAST_JOIN_GROUP. Note that we must call rt6_lookup() and dev_hold() under RCU. If rt6_lookup() returns an entry from the exception table, dst_dev_put() could change rt->dev.dst to loopback concurrently, and the original device could lose the refcount before dev_hold() and unblock device registration. dst_dev_put() is called from NETDEV_UNREGISTER and synchronize_net() follows it, so as long as rt6_lookup() and dev_hold() are called within the same RCU critical section, the dev is alive. Even if the race happens, they are synchronised by idev->dead and mcast addresses are cleaned up. For the racy access to rt->dst.dev, we use dst_dev(). Signed-off-by: Kuniyuki Iwashima Reviewed-by: Eric Dumazet Link: https://patch.msgid.link/20250702230210.3115355-7-kuni1840@gmail.com Signed-off-by: Jakub Kicinski Signed-off-by: Sasha Levin --- net/ipv6/ipv6_sockglue.c | 2 -- net/ipv6/mcast.c | 24 +++++++++++++----------- 2 files changed, 13 insertions(+), 13 deletions(-) diff --git a/net/ipv6/ipv6_sockglue.c b/net/ipv6/ipv6_sockglue.c index c2ea92c0f9166..385321a43a19b 100644 --- a/net/ipv6/ipv6_sockglue.c +++ b/net/ipv6/ipv6_sockglue.c @@ -121,11 +121,9 @@ static bool setsockopt_needs_rtnl(int optname) { switch (optname) { case IPV6_ADDRFORM: - case IPV6_ADD_MEMBERSHIP: case IPV6_DROP_MEMBERSHIP: case IPV6_JOIN_ANYCAST: case IPV6_LEAVE_ANYCAST: - case MCAST_JOIN_GROUP: case MCAST_LEAVE_GROUP: case MCAST_JOIN_SOURCE_GROUP: case MCAST_LEAVE_SOURCE_GROUP: diff --git a/net/ipv6/mcast.c b/net/ipv6/mcast.c index 212c2d8efe0f5..61046543302d4 100644 --- a/net/ipv6/mcast.c +++ b/net/ipv6/mcast.c @@ -172,14 +172,12 @@ static int unsolicited_report_interval(struct inet6_dev *idev) static int __ipv6_sock_mc_join(struct sock *sk, int ifindex, const struct in6_addr *addr, unsigned int mode) { - struct net_device *dev = NULL; - struct ipv6_mc_socklist *mc_lst; struct ipv6_pinfo *np = inet6_sk(sk); + struct ipv6_mc_socklist *mc_lst; struct net *net = sock_net(sk); + struct net_device *dev = NULL; int err; - ASSERT_RTNL(); - if (!ipv6_addr_is_multicast(addr)) return -EINVAL; @@ -199,13 +197,18 @@ static int __ipv6_sock_mc_join(struct sock *sk, int ifindex, if (ifindex == 0) { struct rt6_info *rt; + + rcu_read_lock(); rt = rt6_lookup(net, addr, NULL, 0, NULL, 0); if (rt) { - dev = rt->dst.dev; + dev = dst_dev(&rt->dst); + dev_hold(dev); ip6_rt_put(rt); } - } else - dev = __dev_get_by_index(net, ifindex); + rcu_read_unlock(); + } else { + dev = dev_get_by_index(net, ifindex); + } if (!dev) { sock_kfree_s(sk, mc_lst, sizeof(*mc_lst)); @@ -216,12 +219,11 @@ static int __ipv6_sock_mc_join(struct sock *sk, int ifindex, mc_lst->sfmode = mode; RCU_INIT_POINTER(mc_lst->sflist, NULL); - /* - * now add/increase the group membership on the device - */ - + /* now add/increase the group membership on the device */ err = __ipv6_dev_mc_inc(dev, addr, mode); + dev_put(dev); + if (err) { sock_kfree_s(sk, mc_lst, sizeof(*mc_lst)); return err; -- 2.53.0