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[209.85.218.44]) by smtp.gmail.com with ESMTPSA id p8-20020a05640243c800b00571fad0647csm302926edc.74.2024.04.20.10.34.34 for (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Sat, 20 Apr 2024 10:34:34 -0700 (PDT) Received: by mail-ej1-f44.google.com with SMTP id a640c23a62f3a-a44f2d894b7so287911666b.1 for ; Sat, 20 Apr 2024 10:34:34 -0700 (PDT) X-Forwarded-Encrypted: i=1; AJvYcCXzECgP10NDd4XmN3U3b2QBAljb5iF4ilfVgim8sNlpiS8lW6ay8EMM65eXuclXSVRvfEuo+RObufEdEE95qw9GZ/vcyFpHDSkARkGp X-Received: by 2002:a17:906:c0c5:b0:a55:339d:bd20 with SMTP id bn5-20020a170906c0c500b00a55339dbd20mr3813061ejb.51.1713634473876; Sat, 20 Apr 2024 10:34:33 -0700 (PDT) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 References: In-Reply-To: From: Linus Torvalds Date: Sat, 20 Apr 2024 10:34:17 -0700 X-Gmail-Original-Message-ID: Message-ID: Subject: Re: [PATCH v2] tty: n_gsm: restrict tty devices to attach To: Tetsuo Handa Cc: Greg Kroah-Hartman , Jiri Slaby , Andrew Morton , "Starke, Daniel" , LKML , linux-security-module Content-Type: text/plain; charset="UTF-8" On Sat, 20 Apr 2024 at 04:12, Tetsuo Handa wrote: > > Since n_gsm is designed to be used for serial port [1], reject attaching to > virtual consoles and PTY devices, by checking tty's device major/minor > numbers at gsmld_open(). If we really just want to restrict it to serial devices, then do something like, this: 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 4036566febcb..24425ef35b2b 100644 --- a/drivers/tty/n_gsm.c +++ b/drivers/tty/n_gsm.c @@ -3629,6 +3629,8 @@ static int gsmld_open(struct tty_struct *tty) if (tty->ops->write == NULL) return -EINVAL; + if (tty->ops->set_serial == NULL) + return -EINVAL; /* Attach our ldisc data */ gsm = gsm_alloc_mux(); which at least matches the current (largely useless) pattern of checking for a write function. I think all real serial sub-drivers already have that 'set_serial()' function, and if there are some that don't, we could just add a dummy for them. No? Alternatively, we could go the opposite way, and have some flag in the line discipline that says "I can be a console", and just check that in tty_set_ldisc() for the console. That would probably be a good idea regardless, but likely requires more effort. But this kind of random major number testing seems wrong. It's trying to deal with the _symptoms_, not some deeper truth. Linus