5.4-stable review patch. If anyone has any objections, please let me know.
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From: Jakub Lewalski jakub.lewalski@nokia.com
[ Upstream commit 6bd697b5fc39fd24e2aa418c7b7d14469f550a93 ]
When two instances of uart devices are probing, a concurrency race can occur. If one thread calls uart_register_driver function, which first allocates and assigns memory to 'uart_state' member of uart_driver structure, the other instance can bypass uart driver registration and call ulite_assign. This calls uart_add_one_port, which expects the uart driver to be fully initialized. This leads to a kernel panic due to a null pointer dereference:
[ 8.143581] BUG: kernel NULL pointer dereference, address: 00000000000002b8 [ 8.156982] #PF: supervisor write access in kernel mode [ 8.156984] #PF: error_code(0x0002) - not-present page [ 8.156986] PGD 0 P4D 0 ... [ 8.180668] RIP: 0010:mutex_lock+0x19/0x30 [ 8.188624] Call Trace: [ 8.188629] ? __die_body.cold+0x1a/0x1f [ 8.195260] ? page_fault_oops+0x15c/0x290 [ 8.209183] ? __irq_resolve_mapping+0x47/0x80 [ 8.209187] ? exc_page_fault+0x64/0x140 [ 8.209190] ? asm_exc_page_fault+0x22/0x30 [ 8.209196] ? mutex_lock+0x19/0x30 [ 8.223116] uart_add_one_port+0x60/0x440 [ 8.223122] ? proc_tty_register_driver+0x43/0x50 [ 8.223126] ? tty_register_driver+0x1ca/0x1e0 [ 8.246250] ulite_probe+0x357/0x4b0 [uartlite]
To prevent it, move uart driver registration in to init function. This will ensure that uart_driver is always registered when probe function is called.
Signed-off-by: Jakub Lewalski jakub.lewalski@nokia.com Signed-off-by: Elodie Decerle elodie.decerle@nokia.com Link: https://lore.kernel.org/r/20250331160732.2042-1-elodie.decerle@nokia.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org Signed-off-by: Sasha Levin sashal@kernel.org --- drivers/tty/serial/uartlite.c | 15 ++++++++++++--- 1 file changed, 12 insertions(+), 3 deletions(-)
diff --git a/drivers/tty/serial/uartlite.c b/drivers/tty/serial/uartlite.c index 9a4049c894f7a..e323e9c0a321e 100644 --- a/drivers/tty/serial/uartlite.c +++ b/drivers/tty/serial/uartlite.c @@ -874,16 +874,25 @@ static struct platform_driver ulite_platform_driver = {
static int __init ulite_init(void) { + int ret; + + pr_debug("uartlite: calling uart_register_driver()\n"); + ret = uart_register_driver(&ulite_uart_driver); + if (ret) + return ret;
pr_debug("uartlite: calling platform_driver_register()\n"); - return platform_driver_register(&ulite_platform_driver); + ret = platform_driver_register(&ulite_platform_driver); + if (ret) + uart_unregister_driver(&ulite_uart_driver); + + return ret; }
static void __exit ulite_exit(void) { platform_driver_unregister(&ulite_platform_driver); - if (ulite_uart_driver.state) - uart_unregister_driver(&ulite_uart_driver); + uart_unregister_driver(&ulite_uart_driver); }
module_init(ulite_init);