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[2a02:3100:aeaf:bd01:78a0:2a2d:507f:c97c]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-4954a2edbe4sm223826745e9.12.2026.07.19.09.08.28 (version=TLS1_3 cipher=TLS_CHACHA20_POLY1305_SHA256 bits=256/256); Sun, 19 Jul 2026 09:08:29 -0700 (PDT) From: Karl Mehltretter To: Greg Kroah-Hartman , Jiri Slaby Cc: Karl Mehltretter , linux-serial@vger.kernel.org, linux-kernel@vger.kernel.org, stable@vger.kernel.org Subject: [PATCH 2/4] serial: core: clear freed pointers on uart_register_driver() failure Date: Sun, 19 Jul 2026 18:08:10 +0200 Message-Id: <20260719160812.35407-3-kmehltretter@gmail.com> X-Mailer: git-send-email 2.39.5 (Apple Git-154) In-Reply-To: <20260719160812.35407-1-kmehltretter@gmail.com> References: <20260719160812.35407-1-kmehltretter@gmail.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit uart_register_driver() leaves freed pointers behind on failure. If tty_alloc_driver() fails, it frees drv->state without clearing it. If tty_register_driver() fails, it also drops the tty driver reference without clearing drv->tty_driver. Several drivers register the uart_driver lazily and use drv->state as an "already registered" sentinel. After a failed registration, the next probe sees the stale pointer, skips re-registration and calls uart_add_one_port() with freed state. The resulting unwind can call uart_unregister_driver() with a NULL or dangling drv->tty_driver and oops in tty_unregister_driver(): Unhandled fault: page domain fault (0x01b) at 0x00000018 PC is at tty_unregister_driver+0x10/0x68 LR is at uart_unregister_driver+0x1c/0x60 Reproduced with failslab fail-nth injection on qemu's raspi1ap board: fail the tty_alloc_driver() allocation during a sysfs bind of the PL011 port, then bind again in the same boot. Clear drv->state after freeing the state array and clear drv->tty_driver after dropping the tty driver reference, as uart_unregister_driver() already does. The tty_register_driver() failure case predates Git history. The tty_alloc_driver() failure case was introduced by commit 9e845abfc8a8 ("serial: fix NULL pointer dereference"), which made that error path return cleanly instead of crashing in put_tty_driver(NULL). Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2") Fixes: 9e845abfc8a8 ("serial: fix NULL pointer dereference") Cc: stable@vger.kernel.org Assisted-by: Claude:claude-fable-5 Signed-off-by: Karl Mehltretter --- drivers/tty/serial/serial_core.c | 2 ++ 1 file changed, 2 insertions(+) diff --git a/drivers/tty/serial/serial_core.c b/drivers/tty/serial/serial_core.c index 887b1dd80ad2..ba9145c5a38a 100644 --- a/drivers/tty/serial/serial_core.c +++ b/drivers/tty/serial/serial_core.c @@ -2777,8 +2777,10 @@ int uart_register_driver(struct uart_driver *drv) for (i = 0; i < drv->nr; i++) tty_port_destroy(&drv->state[i].port); tty_driver_kref_put(normal); + drv->tty_driver = NULL; out_kfree: kfree(drv->state); + drv->state = NULL; out: return retval; } -- 2.53.0