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Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni , Stephen Hemminger , netdev@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH net v4 1/3] netconsole: finish enabling the target before releasing RTNL Message-ID: References: <20261021-netcons-fixes-v4-0-3857120c6340@gmail.com> <20261021-netcons-fixes-v4-1-3857120c6340@gmail.com> X-Mailing-List: linux-kernel@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=us-ascii Content-Disposition: inline In-Reply-To: <20261021-netcons-fixes-v4-1-3857120c6340@gmail.com> X-Debian-User: leitao 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 Reviewed-by: Breno Leitao