From: Breno Leitao <leitao@debian.org>
To: Gustavo Luiz Duarte <gustavold@gmail.com>
Cc: Andrew Lunn <andrew+netdev@lunn.ch>,
"David S. Miller" <davem@davemloft.net>,
Eric Dumazet <edumazet@kernel.org>,
Jakub Kicinski <kuba@kernel.org>,
Paolo Abeni <pabeni@redhat.com>,
Stephen Hemminger <stephen@networkplumber.org>,
netdev@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH net v4 1/3] netconsole: finish enabling the target before releasing RTNL
Date: Mon, 26 Oct 2026 04:46:18 -0700 [thread overview]
Message-ID: <at89fwMimRz6FU8K@gmail.com> (raw)
In-Reply-To: <20261021-netcons-fixes-v4-1-3857120c6340@gmail.com>
On Wed, Oct 21, 2026 at 03:19:05PM +0100, Gustavo Luiz Duarte wrote:
> netcons_netpoll_setup() publishes nt->np.dev inside __netpoll_setup(),
> then releases the RTNL and waits for an RCU grace period before
> returning. Only after that does its caller store STATE_ENABLED.
>
> A NETDEV_UNREGISTER event landing in that window tears the target down
> and we end up storing STATE_ENABLED with a NULL np->dev, leading to a
> null-ptr-deref in netconsole_write():
>
> BUG: KASAN: null-ptr-deref in netconsole_write+0xb9/0x7f0
> Read of size 8 at addr 00000000000000a8 by task pr/netcon_ext0/135
> netconsole_write+0xb9/0x7f0
> nbcon_emit_next_record+0x501/0x550
> nbcon_emit_one+0x10e/0x170
> nbcon_kthread_func+0x2ff/0x3b0
> kthread+0x199/0x1e0
>
> Store STATE_ENABLED before dropping the RTNL lock to avoid racing with
> netconsole_netdev_event().
>
> Fixes: 2382b15bcc39 ("netconsole: take care of NETDEV_UNREGISTER event")
> Signed-off-by: Gustavo Luiz Duarte <gustavold@gmail.com>
Reviewed-by: Breno Leitao <leitao@debian.org>
next prev parent reply other threads:[~2026-10-26 11:46 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-10-21 14:19 [PATCH net v4 0/3] netconsole: fix target enable race and configfs read locking Gustavo Luiz Duarte
2026-10-21 14:19 ` [PATCH net v4 1/3] netconsole: finish enabling the target before releasing RTNL Gustavo Luiz Duarte
2026-10-26 11:46 ` Breno Leitao [this message]
2026-10-21 14:19 ` [PATCH net v4 2/3] netconsole: read np.dev under target_list_lock in local_mac_show() Gustavo Luiz Duarte
2026-10-26 11:52 ` Breno Leitao
2026-10-21 14:19 ` [PATCH net v4 3/3] netconsole: recheck device registration after waiting for carrier Gustavo Luiz Duarte
2026-10-25 14:40 ` netdev-bot+sashiko
2026-10-27 9:13 ` Paolo Abeni
2026-10-27 9:18 ` Breno Leitao
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