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[61.220.246.151]) by smtp.gmail.com with ESMTPSA id d2e1a72fcca58-8614f874e9csm5652398b3a.8.2026.09.08.06.04.08 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 08 Sep 2026 06:04:12 -0700 (PDT) From: Potin Lai Date: Tue, 08 Sep 2026 21:01:32 +0800 Subject: [PATCH v2 2/2] net/ncsi: fix use-after-free in ncsi_unregister_dev() Precedence: bulk X-Mailing-List: linux-kernel@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: <20260908-ncsi-over-usb-v2-2-92dd78272fbd@gmail.com> References: <20260908-ncsi-over-usb-v2-0-92dd78272fbd@gmail.com> In-Reply-To: <20260908-ncsi-over-usb-v2-0-92dd78272fbd@gmail.com> To: Andrew Lunn , "David S. Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni , Oliver Neukum , Samuel Mendoza-Jonas , Paul Fertser , Simon Horman Cc: Potin Lai , linux-usb@vger.kernel.org, netdev@vger.kernel.org, linux-kernel@vger.kernel.org, Cosmo Chou , Mike Hsieh , Mik Lin , Potin Lai , Adrian Ambrozewicz X-Mailer: b4 0.15.2 X-Developer-Signature: v=1; a=ed25519-sha256; t=1788872639; l=3964; i=potin.lai.pt@gmail.com; s=20260522; h=from:subject:message-id; bh=bKp+fXghJ6cQJaZb9/dKdTBINAk3RYvGYETZo/GwPjY=; b=zdJASea/GkvdKgFd9ycSXVpHjAiOck4Qf6FmC5wriN7PkcPVxeK0Of7uZPoxbxIv9lDiuHaMb bpOB7UgUOsMBEZNJ8JbUC7iTw3mBtga44fuYe9Mf5IH7tK/XUP9JmwV X-Developer-Key: i=potin.lai.pt@gmail.com; a=ed25519; pk=j3/nMxzz1ZPpp1revghyZ8IqOnwi6RWfuxXN2XrNMRE= From: Adrian Ambrozewicz ncsi_unregister_dev() frees the ncsi_dev_priv structure while timers and workqueue may still be accessing it, causing use-after-free. The problem involves two async mechanisms: 1. Request timers (ncsi_request_timeout) - fire when NCSI responses are not received in time 2. Workqueue (ncsi_dev_work) - processes NCSI state machine These can cascade: timer handlers call ncsi_free_request() which may call schedule_work(), and work can send commands that arm new timers. The fix adds proper synchronization before kfree(): dev_remove_pack() - stop packet reception timer_delete_sync() x 256 - cancel all request timers cancel_work_sync() - wait for workqueue to complete kfree(ndp) Order matters: timers must be cancelled before work because timer handlers may schedule new work via ncsi_free_request(). Note: ncsi_dev_work() is non-blocking - it sends a command, arms a timer, and returns immediately. It does not wait for timer completion. The timer firing later triggers schedule_work() for the next state. So cancel_work_sync() will not hang waiting for cancelled timers. This relies on ncsi_stop_dev() being called first (guaranteed by the network device lifecycle). ncsi_stop_dev() sets state to ncsi_dev_state_functional, which causes ncsi_dev_work() to exit immediately without sending commands or arming timers. This breaks the timer<->work cycle and ensures the synchronization terminates. Timeline showing the race (without fix): CPU 0 (unregister) CPU 1 (async) ------------------ ------------- ncsi_unregister_dev() dev_remove_pack() ncsi_request_timeout() ncsi_free_request() schedule_work() kfree(ndp) ncsi_dev_work() ndp->... <- UAF! With fix: CPU 0 (unregister) CPU 1 (async) ------------------ ------------- ncsi_unregister_dev() dev_remove_pack() timer_delete_sync() x 256 <- waits for timer handlers ncsi_request_timeout() ncsi_free_request() schedule_work() cancel_work_sync() <- waits for work ncsi_dev_work() state=0x100, exits immediately kfree(ndp) <- safe Signed-off-by: Adrian Ambrozewicz Signed-off-by: Potin Lai --- net/ncsi/ncsi-manage.c | 19 +++++++++++++++++++ 1 file changed, 19 insertions(+) diff --git a/net/ncsi/ncsi-manage.c b/net/ncsi/ncsi-manage.c index 54d0df0a9efe..15d7e4cabf4f 100644 --- a/net/ncsi/ncsi-manage.c +++ b/net/ncsi/ncsi-manage.c @@ -1957,9 +1957,28 @@ void ncsi_unregister_dev(struct ncsi_dev *nd) struct ncsi_dev_priv *ndp = TO_NCSI_DEV_PRIV(nd); struct ncsi_package *np, *tmp; unsigned long flags; + int i; dev_remove_pack(&ndp->ptype); + /* + * Synchronize with async operations before freeing ndp. + * + * Note: The caller must have called ncsi_stop_dev() first, which + * sets nd->state to ncsi_dev_state_functional (0x100). This causes + * any running or scheduled ncsi_dev_work() to exit immediately + * without sending commands or arming new timers, breaking the + * potential cycle of: work -> arm timer -> timer -> schedule work. + * + * Order matters: + * 1. timer_delete_sync() - cancel timers, handlers may schedule work + * 2. cancel_work_sync() - cancel work scheduled by timer handlers + */ + for (i = 0; i < ARRAY_SIZE(ndp->requests); i++) + timer_delete_sync(&ndp->requests[i].timer); + + cancel_work_sync(&ndp->work); + list_for_each_entry_safe(np, tmp, &ndp->packages, node) ncsi_remove_package(np); -- 2.52.0