linux-kernel - Re: [PATCH v2] tty: serial: uartlite: register uart driver in init

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Message-ID: <2025032651-quote-kettle-6457@gregkh>
Date: Wed, 26 Mar 2025 15:01:32 +0100
From: Greg KH <gregkh@...uxfoundation.org>
To: Elodie Decerle <elodie.decerle@...ia.com>
Cc: jacmet@...site.dk, jirislaby@...nel.org, linux-serial@...r.kernel.org,
	linux-kernel@...r.kernel.org, jakub.lewalski@...ia.com
Subject: Re: [PATCH v2] tty: serial: uartlite: register uart driver in init

On Wed, Mar 26, 2025 at 11:04:57AM +0100, Elodie Decerle wrote:
> From: Jakub Lewalski <jakub.lewalski@...ia.com>
> 
> 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@...ia.com>
> Tested-by: Elodie Decerle <elodie.decerle@...ia.com>

If you forward on a patch from someone else, you also have to sign off
on it.  Please read our documentation for what this means.

> 
> Changes since v1:
> - Remove mutex lock in uart_register_driver
> - Move uart driver registration to init function (Greg's feedback)

The changes stuff goes below the:

> ---

line.

Again, our documentation should explain this.

thanks,

greg k-h