From: Daniel Starke daniel.starke@siemens.com
[ 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: e1eaea46bb40 ("tty: n_gsm line discipline") Signed-off-by: Daniel Starke daniel.starke@siemens.com Link: https://lore.kernel.org/r/20220701061652.39604-9-daniel.starke@siemens.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org Signed-off-by: Sasha Levin sashal@kernel.org --- drivers/tty/n_gsm.c | 21 +++++++++++++++++---- 1 file changed, 17 insertions(+), 4 deletions(-)
diff --git a/drivers/tty/n_gsm.c b/drivers/tty/n_gsm.c index 39359274096d..9a3d7db33394 100644 --- a/drivers/tty/n_gsm.c +++ b/drivers/tty/n_gsm.c @@ -2859,11 +2859,24 @@ 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); - set_bit(TTY_DO_WRITE_WAKEUP, &tty->flags); - return -ENOBUFS; + ret = tty->ops->write(tty, buf, nr); + else + set_bit(TTY_DO_WRITE_WAKEUP, &tty->flags); + spin_unlock_irqrestore(&gsm->tx_lock, flags); + + return ret; }
/**