linux-kernel - Re: [PATCH] tty: n_gsm: add missing tty_kref

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Message-ID: <8e7d4214-01b8-d1a7-adaf-f2135cb6431a@kernel.org>
Date:   Tue, 9 Nov 2021 18:33:14 +0100
From:   Jiri Slaby <jirislaby@...nel.org>
To:     Pavel Skripkin <paskripkin@...il.com>, gregkh@...uxfoundation.org,
        hdanton@...a.com
Cc:     linux-kernel@...r.kernel.org
Subject: Re: [PATCH] tty: n_gsm: add missing tty_kref_put

On 09. 11. 21, 11:39, Pavel Skripkin wrote:
> My local syzbot instance hit memory leak in gsmld_attach_gsm(). The
> reproducer injects allocation failure in tty_register_device(). After
> this error only previous tty_register_device() calls unwinded, but not
> tty_kref_get().
> 
> It leads to tty_struct leak, because ->close() won't be called in case
> of ->open() failure and nothing puts tty reference.

I don't have time to check the n_gsm case now (like: are you talking 
about tty->open/close or file_ops->open/close -- they behave 
differently), but tty definitely calls close even if open fails.

> Fixes: 0a360e8b65d6 ("tty: n_gsm: check error while registering tty devices")
> Signed-off-by: Pavel Skripkin <paskripkin@...il.com>
> ---
>   drivers/tty/n_gsm.c | 2 ++
>   1 file changed, 2 insertions(+)
> 
> diff --git a/drivers/tty/n_gsm.c b/drivers/tty/n_gsm.c
> index 1d92d2a84889..1cc3aec17d2d 100644
> --- a/drivers/tty/n_gsm.c
> +++ b/drivers/tty/n_gsm.c
> @@ -2394,6 +2394,8 @@ static int gsmld_attach_gsm(struct tty_struct *tty, struct gsm_mux *gsm)
>   				for (i--; i >= 1; i--)
>   					tty_unregister_device(gsm_tty_driver,
>   								base + i);
> +
> +				tty_kref_put(gsm->tty);
>   				return PTR_ERR(dev);
>   			}
>   		}
> 


-- 
js
suse labs