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tty: n_gsm: fix race condition in gsmld_write() 

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: e1eaea46bb ("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>
This commit is contained in:
Daniel Starke 2022-07-01 08:16:52 +02:00 committed by Greg Kroah-Hartman
parent 4fae831b3a
commit 32dd59f969
1 changed files with 17 additions and 4 deletions
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21
drivers/tty/n_gsm.c
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@ -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;
}
/**