Messages in this thread Patch in this message | | | From | "D. Starke" <> | Subject | [PATCH v3 9/9] tty: n_gsm: fix race condition in gsmld_write() | Date | Mon, 30 May 2022 16:45:12 +0200 |
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From: Daniel Starke <daniel.starke@siemens.com>
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") Cc: stable@vger.kernel.org Signed-off-by: Daniel Starke <daniel.starke@siemens.com> --- drivers/tty/n_gsm.c | 21 +++++++++++++++++---- 1 file changed, 17 insertions(+), 4 deletions(-)
There have been no comments on v2, hence, no change was done.
Link: https://lore.kernel.org/all/20220519070757.2096-9-daniel.starke@siemens.com/
diff --git a/drivers/tty/n_gsm.c b/drivers/tty/n_gsm.c index b0b093e8e9d9..afd179a8481d 100644 --- a/drivers/tty/n_gsm.c +++ b/drivers/tty/n_gsm.c @@ -2999,11 +2999,24 @@ 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; } /** -- 2.34.1
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