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Tue, 06 Oct 2026 11:22:29 -0700 (PDT) From: Gustavo Luiz Duarte Date: Tue, 06 Oct 2026 19:21:25 +0100 Subject: [PATCH net v2 1/2] netconsole: finish enabling the target before releasing RTNL Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit Message-Id: <20261006-netcons-fixes-v2-1-ca652d55fd4a@gmail.com> References: <20261006-netcons-fixes-v2-0-ca652d55fd4a@gmail.com> In-Reply-To: <20261006-netcons-fixes-v2-0-ca652d55fd4a@gmail.com> To: Breno Leitao , Andrew Lunn , "David S. Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni , Stephen Hemminger Cc: Gustavo Luiz Duarte , netdev@vger.kernel.org, linux-kernel@vger.kernel.org X-Mailer: b4 0.15.2 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 --- drivers/net/netconsole.c | 11 +++++------ 1 file changed, 5 insertions(+), 6 deletions(-) diff --git a/drivers/net/netconsole.c b/drivers/net/netconsole.c index b358e5c36735..1fb846ad07d1 100644 --- a/drivers/net/netconsole.c +++ b/drivers/net/netconsole.c @@ -552,13 +552,16 @@ static int netcons_netpoll_setup(struct netconsole_target *nt) err = __netpoll_setup(np, ndev); if (err) goto put; - rtnl_unlock(); /* Make sure all NAPI polls which started before dev->npinfo * was visible have exited before we start calling NAPI poll. * NAPI skips locking if dev->npinfo is NULL. + * Hold RTNL until enable is finished so we don't race with + * netconsole_netdev_event() */ - synchronize_rcu(); + synchronize_net(); + nt->state = STATE_ENABLED; + rtnl_unlock(); return 0; @@ -589,7 +592,6 @@ static void resume_target(struct netconsole_target *nt) return; } - nt->state = STATE_ENABLED; pr_info("network logging resumed on interface %s\n", nt->np.dev_name); } @@ -1067,7 +1069,6 @@ static ssize_t enabled_store(struct config_item *item, goto out_unlock; } - nt->state = STATE_ENABLED; pr_info("network logging started\n"); } else { /* false */ /* We need to disable the netconsole before cleaning it up @@ -2669,8 +2670,6 @@ static struct netconsole_target *alloc_param_target(char *target_config, * otherwise, keep the target in the list, but disabled. */ goto fail; - } else { - nt->state = STATE_ENABLED; } populate_configfs_item(nt, cmdline_count); -- 2.55.0