From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.remote-ip=74.125.229.8 ARC-Seal: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; cv=none; t=1793205445; b=lsE7DXMa+sAarw7WBkWz8d1WTtmF58KF1Gy8aWCVsapcy0X8rRk6uy1NRdUTZH+UzqsD +2F99yaKLIIRAkqBP9lCD477I6p93K7396N5mq5ZsPPldBfP7nqctzWRmizi4zK+zzArf i4iPLgMUeWFYXOij05P6jiI/RpFyonMA1I4R+qV/raCHxk3tA4i3LHROfYi5qjhpuVrOm IRqbF0l2iJtax3oFBGSpSFzHlbF6iDLmRmRgWQ9BoB1vB9lvT+ui9PfpNEMcALFgU+3xb QO8X1xzXG5hXFReLGmBVkhhhDom6nNkyVhPgZsazTIy4OepLXo8avbdWR548PU2u2tw== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1793205445; h=DMARC-Filter:Received:DKIM-Signature:X-Google-DKIM-Signature: X-Forwarded-Encrypted:X-Gm-Message-State:X-Gm-Gg:X-Received:Received: Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; bh=l+8ehmPAo6inV+YH732cihXHH/Y9Bk9COvdt/G9UfJY=; b=lVU03OX7r4WKhafNpLt1aai32J/eyelIBBnoGaeunMDf38WbcFo4VC+r8hEUw14pXHwE xA4ra8mPlHE4uz/pdqDO8K1WLKTi5Ca3VdkArH+VvXmkXYNeCFSE/UFPV6Rye53W3H0vD wFi8/6vUw2slhbfwTxaYYS38T4hfk688+LWQY931EVSJfzC1ZpUFVp4a2IjlyFUFNC+de 5e8klf/qXPylBUew2LAMAVsPjyynrHIECrrPfXXHFj5RGvjqAzHQvwIqu7LpIsw7wB+4Y vdnqiq14osqCEUeuFjKEPo6aiQykX6EwlDDrz/nG/rpuKNE2Q1DRDh79ovkEW9I8yRg== ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass header.from=gmail.com; spf=pass smtp.mailfrom=gmail.com; dkim=pass header.d=gmail.com header.i=@gmail.com header.a=rsa-sha256 header.s=20260707 header.b=yjieG5eT; arc=none smtp.remote-ip=74.125.229.8 Received: from mail-dy2-f8.google.com (mail-dy2-f8.google.com [74.125.229.8]) (using TLSv1.3 with cipher TLS_AES_128_GCM_SHA256 (128/128 bits) key-exchange X25519 server-signature ECDSA (prime256v1) server-digest SHA256) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id B72E060A261E for ; Wed, 28 Oct 2026 16:37:24 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.2 smtp.subspace.kernel.org B72E060A261E Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=gmail.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=gmail.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key, unprotected) header.d=gmail.com header.i=@gmail.com header.a=rsa-sha256 header.s=20260707 header.b=yjieG5eT Received: by mail-dy2-f8.google.com with SMTP id 5a478bee46e88-36a24f47293so479743eec.0 for ; Wed, 28 Oct 2026 09:37:24 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20260707; t=1793205444; x=1793810244; darn=vger.kernel.org; h=in-reply-to:content-disposition:content-type:mime-version :references:message-id:subject:cc:to:from:date:from:to:cc:subject :date:message-id:reply-to:content-type; bh=l+8ehmPAo6inV+YH732cihXHH/Y9Bk9COvdt/G9UfJY=; b=yjieG5eTsxf2hNickEyx4oaFBkQeyXAr7t4GUk0Bq82KubByGt9kiMmNFKBzZRPnNA Oac51001wrooxkjqnfUmFoxmXb7gISVTvCnIoAgJkqixiqChuXzIWN6I//CsSEHkfn+G 31MhqGnd4YivrCKyPeP8gdDF2KOz4sU4uMbqRVT7nja94oTEij+1Lu08slxLLAbv63AT WhVn1YDBR2MaCr46SnsB5DuKIegKMmrWlHT0WkFq1Nchnn8seRO6pn5+Q8wIu38knrp1 ZvQ9sZqBhmD3WdB7452IkMLC4N1Lf++dPL6Fe9hoQVxGCekD0iijf6y5Xc59I8wzB1kM 1KXw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20260707; t=1793205444; x=1793810244; h=in-reply-to:content-disposition:content-type:mime-version :references:message-id:subject:cc:to:from:date:x-gm-gg :x-gm-message-state:from:to:cc:subject:date:message-id:reply-to :content-type; bh=l+8ehmPAo6inV+YH732cihXHH/Y9Bk9COvdt/G9UfJY=; b=P/RjSrKA4EmlyjlaqjgW1McXQvNX4qGO7jTaXynGgBexIFovJVJ1C88AxMapL0xXxk Bck99/7VnBBOFRbmL5L+izvRHThx6oveOg7YYUFjn1p+mPqpQZqaVTS3R3QDCJiQLdy1 Py8fcVVuBJ++2Kj6xHXnsqE413t32NckpOVDYs/6hP6OFQi4Q1N7Jzi3+1zuxqYvUnhG xxcocW/nxd12TNrGZxH5LEqzADpF8Vh0kC2eIH55ScXQAbop2/MhI3voMBjIktjKYmK2 bIgS+H4myKFQOw9NZCNRDVCmXbVPElxILCYsE12PjqosL9lLlNRPDjWytTS5vrGBLrOo /D5Q== X-Forwarded-Encrypted: i=1; AKwUvBxihurf+uYUJ8ad2VGKzt0NQQoC3oAeetdtRzNBidTSGt2FvX5kzsdXMZS7JmzqQel9KvYmPPw=@vger.kernel.org X-Gm-Message-State: AFq9FYJ3R/2gGW3+KqAXmxYLmWgN4gJhwumCkStqbM+x93yMoFuFusQI tMrUlRAYeWFmPYgS/PxmkOUo2JBxJcPP5pCR5IvHYIQsXebGt31t/Se5 X-Gm-Gg: AYBFou1gze870Q20e+56CoAvLC7mSQrVng0zX33ABTWQTy3itKO6ZeqQtd8tiEqKGce etpCyaZrgdWWAyipp7dmwWXD/Bro7CpTnr7KAjVgnmGpbf71bYjJlMIMpRQm6IxFXWX5g7MRl9Y Oh7lIGLy7AVYuIDj8bJvQWeRnnRXnbWUyqET77cAfYm0umm5H3nk3xyoTFupq2zT/goLPXC3hAu f/oIASNx+O1vYv0E47takHouz6If7pO6uyohvcl67miKcKAz+hS9x1P704kTXGjBbPFaW8tKYkA yrz6hjW7mdJwTLLLvQe1NA/48Bj+4JuQ1atJYegGfkjSHNZYyksMydOxkenCyK0Pipfwb2j3ch6 mogbHXCgCbYZAtvlng6RwDY7jUq+4fF0paxlrK9apINVUzp1NDvssejJ2zVJ9qlKPL49RET/HgV aqQX9Ewl1gsOHNeBcyb2Wx3i5ckJ1vVCMw5Tj2T13L5faxtfe6SAF1EfEfNvuas+466FS43UvFX VfschDsvvtnQ/SLe2Wx4XKtnoQh9mvtT6wbm+HqWwbLq0HbNi+6sP+TtbfKTihQEXPb8YqdPWOe XQDHyQXvM0FzRfsS8faQeMc= X-Received: by 2002:a05:693c:88c7:20b0:35a:22a4:12a with SMTP id 5a478bee46e88-36a203af6e9mr4489164eec.18.1793205443455; Wed, 28 Oct 2026 09:37:23 -0700 (PDT) Received: from localhost ([2a03:2880:9ff:61::]) by smtp.gmail.com with ESMTPSA id 5a478bee46e88-36a2390929asm9638344eec.12.2026.10.28.09.37.22 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 28 Oct 2026 09:37:22 -0700 (PDT) Date: Wed, 28 Oct 2026 09:37:17 -0700 From: Stanislav Fomichev To: Kuniyuki Iwashima Cc: Naman Gulati , "David S . Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni , Simon Horman , netdev@vger.kernel.org, linux-kernel@vger.kernel.org, syzbot+1269fe6cc2016008124e@syzkaller.appspotmail.com Subject: Re: [PATCH net] netdev-genl: ignore NETDEV_UNREGISTER rebroadcasts Message-ID: References: <20261026221306.3151025-1-namangulati@google.com> X-Mailing-List: netdev@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: On 10/27, Kuniyuki Iwashima wrote: > On Mon, 26 Oct 2026 15:28:44 -0700, Stanislav Fomichev wrote: > > On 10/26, Naman Gulati wrote: > > > netdev_wait_allrefs_any() re-sends NETDEV_UNREGISTER every second while > > > it waits for the last references on a device to be dropped. By then > > > netdev_run_todo() has already marked the device NETREG_UNREGISTERED and > > > RTNL has been dropped at least once since the initial notification sent > > > by unregister_netdevice_many_notify(). > > > > > > netdev_genl_netdevice_event() does not tell these rebroadcasts apart > > > from the initial notification and sends a NETDEV_CMD_DEV_DEL_NTF > > > multicast for each of them. At best this spams NETDEV_NLGRP_MGMT > > > listeners with duplicate notifications; at worst the pernet state of > > > the netns the device belongs to is already gone and the handler > > > dereferences a NULL pointer. > > > > > > default_device_exit_batch() only unregisters the devices still listed > > > in the exiting netns; it does not wait for in-flight unregistrations of > > > devices that were already unlisted (the barrier doing that was removed > > > by commit 8a4fc54b07d7 ("net: get rid of rtnl_lock_unregistering()")). > > > So when a device is unregistered by something other than the > > > cleanup_net() of its own netns while references on it are still held, > > > e.g. a veth whose peer in another netns gets deleted, and that netns > > > exits while the device is stuck in netdev_wait_allrefs_any(), the > > > remaining pernet exit handlers run and genl_pernet_exit() sets > > > net->genl_sock to NULL. The next rebroadcast then crashes in > > > genl_has_listeners(): > > > > > > BUG: KASAN: null-ptr-deref in netlink_has_listeners+0x3d/0x3f0 net/netlink/af_netlink.c:1388 > > > Read of size 8 at addr 0000000000000578 by task syz.0.0/5325 > > > Call Trace: > > > > > > netlink_has_listeners+0x3d/0x3f0 net/netlink/af_netlink.c:1388 > > > genl_has_listeners include/net/genetlink.h:644 [inline] > > > netdev_genl_dev_notify+0x161/0x450 net/core/netdev-genl.c:93 > > > netdev_genl_netdevice_event+0x98/0x3c0 net/core/netdev-genl.c:1491 > > > notifier_call_chain+0x1a5/0x3d0 kernel/notifier.c:85 > > > netdev_wait_allrefs_any net/core/dev.c:11690 [inline] > > > netdev_run_todo+0x731/0x1060 net/core/dev.c:11808 > > > rtnl_unlock net/core/rtnetlink.c:157 [inline] > > > rtnl_dellink+0x68f/0x810 net/core/rtnetlink.c:3707 > > > > > > syzbot hit this by moving one end of a veth pair into a short-lived > > > netns while netdevsim's deferred FIB event processing still held a > > > reference on it, and then deleting the other end (repro [1]). While the > > > source of this bug is netdevsim deferring FIB processing for and holding > > > onto the device reference for O(seconds) which is being fixed > > > separately [2], any driver may introduce such a delay and trigger the > > > null-ptr-deref. > > > > > > Skip the rebroadcasts, which are the only NETDEV_UNREGISTER events > > > delivered with reg_state == NETREG_UNREGISTERED. The notifications sent > > > by unregister_netdevice_many_notify() and, for a device leaving a netns, > > > by __dev_change_net_namespace() are issued under RTNL in the same > > > critical section that unlists the device, before its netns can be torn > > > down, and keep being handled. This mirrors what ip6_route_dev_notify() > > > already does to cope with the rebroadcasts. > > > > > > This change should not break the UAPI spec as it defines dev-del-ntf as > > > a "Notification about device disappearing." which is a single event. The > > > rebroadcast in netdev_wait_allrefs_any() exists to re-kick in-kernel > > > subsystems holding references; netdev-genl happens to be on the notifier > > > chain and forwards it. > > > > > > [1] https://gist.github.com/NamanGulati/2d1b49b8757f9a88b0bd6e55018c02ae > > > [2] https://lore.kernel.org/r/20261023191517.607834-1-kuniyu@google.com > > > > > > Fixes: d3d854fd6a1d ("netdev-genl: create a simple family for netdev stuff") > > > Reported-by: syzbot+1269fe6cc2016008124e@syzkaller.appspotmail.com > > > Closes: https://lore.kernel.org/netdev/6adf9f64.6200f071.51519.0ed1.GAE@google.com/ > > > Reviewed-by: Kuniyuki Iwashima > > > Signed-off-by: Naman Gulati > > > --- > > > Note that the reproducer attached to the syzbot bug targets a different > > > bug (via devlink_port_notify() on netns teardown) that happens to share > > > the same crash title, not the one in the original reported crash report. > > > --- > > > net/core/netdev-genl.c | 6 ++++++ > > > 1 file changed, 6 insertions(+) > > > > > > diff --git a/net/core/netdev-genl.c b/net/core/netdev-genl.c > > > index 33b9f4eb9565a..2032ab9a864c2 100644 > > > --- a/net/core/netdev-genl.c > > > +++ b/net/core/netdev-genl.c > > > @@ -1487,6 +1487,12 @@ static int netdev_genl_netdevice_event(struct notifier_block *nb, > > > netdev_unlock_full_to_ops(netdev); > > > break; > > > case NETDEV_UNREGISTER: > > > + /* netdev_wait_allrefs_any() rebroadcasts NETDEV_UNREGISTER > > > + * while waiting for the last references to be dropped; the > > > + * netns may already be torn down by then. Notify only once. > > > + */ > > > > [..] > > > > > + if (READ_ONCE(netdev->reg_state) == NETREG_UNREGISTERED) > > > + break; > > > > Same as > > https://lore.kernel.org/netdev/20261026063743.1797-1-lege.wang@jaguarmicro.com/ > > ? > > > > reg_state is protected by netdev, why not do this under netdev_lock? > > Also seems like we are fixing a symptom, not the problem? > > fwiw, I suggested not to take the lock since we are only interested > in NETREG_UNREGISTERED here and there is a clear ordering in the case. > > The root cause is netdevsim this time, and I have a fix, > > https://syzkaller.appspot.com/text?tag=Patch&x=15923c21580000 > > but rebroadcast itself is not-ideal-but-valid behaviour, so each > NETDEV_UNREGISTER must be idempotent unless we can completley remove > the rebroadcast mechanism itself in the future. (to both you and Naman) Idk, I haven't looked deep into that, it just reads a bit weird that we call the notifiers only then to filter (some of?) them out later. While this patch might fix a narrow race I wonder if we are missing a bigger picture (for example, why not get back to pre commit 8a4fc54b07d7 state?).