This is a note to let you know that I've just added the patch titled
tty: n_gsm: fix race condition in gsmld_write()
to the 4.9-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
tty-n_gsm-fix-race-condition-in-gsmld_write.patch
and it can be found in the queue-4.9 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
commit 6574e22c5225ebeb8b1b3ad9cd3febc9ed10df96
Author: Daniel Starke <daniel.starke@xxxxxxxxxxx>
Date: Fri Jul 1 08:16:52 2022 +0200
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: e1eaea46bb40 ("tty: n_gsm line discipline")
Signed-off-by: Daniel Starke <daniel.starke@xxxxxxxxxxx>
Link: https://lore.kernel.org/r/20220701061652.39604-9-daniel.starke@xxxxxxxxxxx
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
diff --git a/drivers/tty/n_gsm.c b/drivers/tty/n_gsm.c
index 01ff3f1b2350..8ab288a4950f 100644
--- a/drivers/tty/n_gsm.c
+++ b/drivers/tty/n_gsm.c
@@ -2521,11 +2521,24 @@ 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;
}
/**
