6.1-stable review patch. If anyone has any objections, please let me know.
------------------
From: Qingfang Deng dqfext@gmail.com
[ Upstream commit 38b04ed7072e54086102eae2d05d03ffcdb4b695 ]
The TTY layer already serializes line discipline operations with tty->ldisc_sem, so the extra disc_data_lock and refcnt in 6pack are unnecessary.
Removing them simplifies the code and also resolves a lockdep warning reported by syzbot. The warning did not indicate a real deadlock, since the write-side lock was only taken in process context with hardirqs disabled.
Reported-by: syzbot+5fd749c74105b0e1b302@syzkaller.appspotmail.com Closes: https://lore.kernel.org/all/68c858b0.050a0220.3c6139.0d1c.GAE@google.com/ Signed-off-by: Qingfang Deng dqfext@gmail.com Reviewed-by: Dan Carpenter dan.carpenter@linaro.org Link: https://patch.msgid.link/20250925051059.26876-1-dqfext@gmail.com Signed-off-by: Paolo Abeni pabeni@redhat.com Signed-off-by: Sasha Levin sashal@kernel.org --- drivers/net/hamradio/6pack.c | 57 ++++-------------------------------- 1 file changed, 5 insertions(+), 52 deletions(-)
diff --git a/drivers/net/hamradio/6pack.c b/drivers/net/hamradio/6pack.c index 9fb5675242207..1b007dd174794 100644 --- a/drivers/net/hamradio/6pack.c +++ b/drivers/net/hamradio/6pack.c @@ -121,8 +121,6 @@ struct sixpack {
struct timer_list tx_t; struct timer_list resync_t; - refcount_t refcnt; - struct completion dead; spinlock_t lock; };
@@ -359,42 +357,13 @@ static void sp_bump(struct sixpack *sp, char cmd)
/* ----------------------------------------------------------------------- */
-/* - * We have a potential race on dereferencing tty->disc_data, because the tty - * layer provides no locking at all - thus one cpu could be running - * sixpack_receive_buf while another calls sixpack_close, which zeroes - * tty->disc_data and frees the memory that sixpack_receive_buf is using. The - * best way to fix this is to use a rwlock in the tty struct, but for now we - * use a single global rwlock for all ttys in ppp line discipline. - */ -static DEFINE_RWLOCK(disc_data_lock); - -static struct sixpack *sp_get(struct tty_struct *tty) -{ - struct sixpack *sp; - - read_lock(&disc_data_lock); - sp = tty->disc_data; - if (sp) - refcount_inc(&sp->refcnt); - read_unlock(&disc_data_lock); - - return sp; -} - -static void sp_put(struct sixpack *sp) -{ - if (refcount_dec_and_test(&sp->refcnt)) - complete(&sp->dead); -} - /* * Called by the TTY driver when there's room for more data. If we have * more packets to send, we send them here. */ static void sixpack_write_wakeup(struct tty_struct *tty) { - struct sixpack *sp = sp_get(tty); + struct sixpack *sp = tty->disc_data; int actual;
if (!sp) @@ -406,7 +375,7 @@ static void sixpack_write_wakeup(struct tty_struct *tty) clear_bit(TTY_DO_WRITE_WAKEUP, &tty->flags); sp->tx_enable = 0; netif_wake_queue(sp->dev); - goto out; + return; }
if (sp->tx_enable) { @@ -414,9 +383,6 @@ static void sixpack_write_wakeup(struct tty_struct *tty) sp->xleft -= actual; sp->xhead += actual; } - -out: - sp_put(sp); }
/* ----------------------------------------------------------------------- */ @@ -436,7 +402,7 @@ static void sixpack_receive_buf(struct tty_struct *tty, if (!count) return;
- sp = sp_get(tty); + sp = tty->disc_data; if (!sp) return;
@@ -452,7 +418,6 @@ static void sixpack_receive_buf(struct tty_struct *tty, } sixpack_decode(sp, cp, count1);
- sp_put(sp); tty_unthrottle(tty); }
@@ -567,8 +532,6 @@ static int sixpack_open(struct tty_struct *tty)
spin_lock_init(&sp->lock); spin_lock_init(&sp->rxlock); - refcount_set(&sp->refcnt, 1); - init_completion(&sp->dead);
/* !!! length of the buffers. MTU is IP MTU, not PACLEN! */
@@ -650,19 +613,11 @@ static void sixpack_close(struct tty_struct *tty) { struct sixpack *sp;
- write_lock_irq(&disc_data_lock); sp = tty->disc_data; - tty->disc_data = NULL; - write_unlock_irq(&disc_data_lock); if (!sp) return;
- /* - * We have now ensured that nobody can start using ap from now on, but - * we have to wait for all existing users to finish. - */ - if (!refcount_dec_and_test(&sp->refcnt)) - wait_for_completion(&sp->dead); + tty->disc_data = NULL;
/* We must stop the queue to avoid potentially scribbling * on the free buffers. The sp->dead completion is not sufficient @@ -686,7 +641,7 @@ static void sixpack_close(struct tty_struct *tty) static int sixpack_ioctl(struct tty_struct *tty, unsigned int cmd, unsigned long arg) { - struct sixpack *sp = sp_get(tty); + struct sixpack *sp = tty->disc_data; struct net_device *dev; unsigned int tmp, err;
@@ -738,8 +693,6 @@ static int sixpack_ioctl(struct tty_struct *tty, unsigned int cmd, err = tty_mode_ioctl(tty, cmd, arg); }
- sp_put(sp); - return err; }