[PATCH v4 1/5] serial: core: do fallible allocations before the console can be registered

serial_core_add_one_port() allocates uport->tty_groups after
uart_configure_port(), which may register the console. If the allocation
fails, the driver unwinds the port while its console remains registered.
The earlier uport->name allocation has a related failure path that leaves
state->uart_port linked to a port being freed.

Failslab reproduced a NULL dereference in PL011 console output and a KASAN
use-after-free in i.MX console output after failed binds.

Allocate the name and tty_groups before linking the port and configuring
it. Reserve space for the optional driver attribute group because
config_port() may populate uport->attr_group during configuration.

Fixes: 266dcff03eed ("Serial: allow port drivers to have a default attribute group")
Fixes: f7048b15900f ("tty: serial_core: Add name field to uart_port struct")
Reported-by: Sashiko <[email protected]>
Closes: https://lore.kernel.org/all/[email protected]/
Assisted-by: Claude:claude-fable-5
Signed-off-by: Karl Mehltretter <[email protected]>
---
 drivers/tty/serial/serial_core.c | 30 ++++++++++++++++--------------
 1 file changed, 16 insertions(+), 14 deletions(-)

diff --git a/drivers/tty/serial/serial_core.c b/drivers/tty/serial/serial_core.c
index a530ad372b43..03ee3d038f4e 100644
--- a/drivers/tty/serial/serial_core.c
+++ b/drivers/tty/serial/serial_core.c
@@ -3056,7 +3056,6 @@ static int serial_core_add_one_port(struct uart_driver *drv, struct uart_port *u
 	struct uart_state *state;
 	struct tty_port *port;
 	struct device *tty_dev;
-	int num_groups;
 
 	if (uport->line >= drv->nr)
 		return -EINVAL;
@@ -3068,6 +3067,22 @@ static int serial_core_add_one_port(struct uart_driver *drv, struct uart_port *u
 	if (state->uart_port)
 		return -EINVAL;
 
+	uport->name = kasprintf(GFP_KERNEL, "%s%u", drv->dev_name,
+				drv->tty_driver->name_base + uport->line);
+	if (!uport->name)
+		return -ENOMEM;
+
+	/*
+	 * uart_configure_port() may set uport->attr_group and register the
+	 * console. Allocate room for both groups and a NULL terminator first.
+	 */
+	uport->tty_groups = kzalloc_objs(*uport->tty_groups, 3);
+	if (!uport->tty_groups) {
+		kfree(uport->name);
+		return -ENOMEM;
+	}
+	uport->tty_groups[0] = &tty_dev_attr_group;
+
 	/* Link the port to the driver state table and vice versa */
 	atomic_set(&state->refcount, 1);
 	init_waitqueue_head(&state->remove_wait);
@@ -3084,10 +3099,6 @@ static int serial_core_add_one_port(struct uart_driver *drv, struct uart_port *u
 	state->pm_state = UART_PM_STATE_UNDEFINED;
 	uart_port_set_cons(uport, drv->cons);
 	uport->minor = drv->tty_driver->minor_start + uport->line;
-	uport->name = kasprintf(GFP_KERNEL, "%s%u", drv->dev_name,
-				drv->tty_driver->name_base + uport->line);
-	if (!uport->name)
-		return -ENOMEM;
 
 	if (uport->cons && uport->dev)
 		of_console_check(uport->dev->of_node, uport->cons->name, uport->line);
@@ -3102,15 +3113,6 @@ static int serial_core_add_one_port(struct uart_driver *drv, struct uart_port *u
 
 	port->console = uart_console(uport);
 
-	num_groups = 2;
-	if (uport->attr_group)
-		num_groups++;
-
-	uport->tty_groups = kzalloc_objs(*uport->tty_groups, num_groups);
-	if (!uport->tty_groups)
-		return -ENOMEM;
-
-	uport->tty_groups[0] = &tty_dev_attr_group;
 	if (uport->attr_group)
 		uport->tty_groups[1] = uport->attr_group;
 
-- 
2.53.0