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Commit fbf97956 authored by Daniel Starke's avatar Daniel Starke Committed by Greg Kroah-Hartman
Browse files

tty: n_gsm: fix race condition in gsmld_write() 



[ Upstream commit 32dd59f96924f45e33bc79854f7a00679c0fa28e ]

The function may be used by the user directly and also by the n_gsm
internal functions. They can lead into a race condition which results in
interleaved frames if both are writing at the same time. The receiving side
is not able to decode those interleaved frames correctly.

Add a lock around the low side tty write to avoid race conditions and frame
interleaving between user originated writes and n_gsm writes.

Fixes: e1eaea46 ("tty: n_gsm line discipline")
Signed-off-by: default avatarDaniel Starke <daniel.starke@siemens.com>
Link: https://lore.kernel.org/r/20220701061652.39604-9-daniel.starke@siemens.com


Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: default avatarSasha Levin <sashal@kernel.org>
parent 597bec4a

drivers/tty/n_gsm.c

+17 −4
Original line number Diff line number Diff line
@@ -2651,11 +2651,24 @@ static ssize_t gsmld_read(struct tty_struct *tty, struct file *file, 
static ssize_t gsmld_write(struct tty_struct *tty, struct file *file,

			   const unsigned char *buf, size_t nr)

{

	int space = tty_write_room(tty);

	struct gsm_mux *gsm = tty->disc_data;

	unsigned long flags;

	int space;

	int ret;



	if (!gsm)

		return -ENODEV;



	ret = -ENOBUFS;

	spin_lock_irqsave(&gsm->tx_lock, flags);

	space = tty_write_room(tty);

	if (space >= nr)

		return tty->ops->write(tty, buf, nr);

		ret = tty->ops->write(tty, buf, nr);

	else

		set_bit(TTY_DO_WRITE_WAKEUP, &tty->flags);

	return -ENOBUFS;

	spin_unlock_irqrestore(&gsm->tx_lock, flags);



	return ret;

}



/**