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charset="utf-8" uart->port.dev will have a value in serial8250_register_8250_port if the port number is under the initial CONFIG_SERIAL_8250_RUNTIME_UARTS. If unset, it will depend upon up->port.dev being set by the particular serial driver. A faulty driver might not set this value and this leads to null pointer dereferenced later in has_acpi_companion and later at uart_add_one_port call: Oops: general protection fault, probably for non-canonical address KASAN: null-ptr-deref in range RIP: 0010:serial8250_register_8250_port+0xd34/0x2030 drivers/tty/serial/8250/8250_core.c Reviewed-by: Jose Javier Rodriguez Barbarin Signed-off-by: Filip Jensen --- Thank you very much for the revision, Jiri. As suggested, I have removed people from the recipients list that have not made relevant changes related to this patch recently. V1 -> V2: Fixed that the return value was not setting an error value. Rewriten the subject to make clear that this is a fix to a posible null pointer deref and slightly rewriten the description for the changelog. V1: https://lore.kernel.org/linux-serial/20260305163358.42599-1-dev-Felipe.= Jensen@duagon.com/ For a case of a low level driver not setting this, cf. Link: https://lore.kernel.org/linux-serial/20260305162815.41818-1-dev-Felip= e.Jensen@duagon.com/ drivers/tty/serial/8250/8250_core.c | 2 ++ 1 file changed, 2 insertions(+) diff --git a/drivers/tty/serial/8250/8250_core.c b/drivers/tty/serial/8250/= 8250_core.c index d2e2c5dfef99..d758f871fbbd 100644 --- a/drivers/tty/serial/8250/8250_core.c +++ b/drivers/tty/serial/8250/8250_core.c @@ -756,6 +756,8 @@ int serial8250_register_8250_port(const struct uart_825= 0_port *up) if (ret) goto err; } + if (!uart->port.dev) + return -EINVAL; =20 if (up->port.flags & UPF_FIXED_TYPE) uart->port.type =3D up->port.type; --=20 2.34.1