From c284ee2cf12b55fa8496b2d098bf0938688f1c1c Mon Sep 17 00:00:00 2001 From: Chao Bi Date: Thu, 17 Oct 2013 15:08:27 +0800 Subject: [PATCH] n_gsm: race between ld close and gsmtty open ttyA has ld associated to n_gsm, when ttyA is closing, it triggers to release gsmttyB's ld data dlci[B], then race would happen if gsmttyB is opening in parallel. Here are race cases we found recently in test: CASE #1 ==================================================================== releasing dlci[B] race with gsmtty_install(gsmttyB), then panic in gsmtty_open(gsmttyB), as below: tty_release(ttyA) tty_open(gsmttyB) | | ----- gsmtty_install(gsmttyB) | | ----- gsm_dlci_alloc(gsmttyB) => alloc dlci[B] tty_ldisc_release(ttyA) ----- | | gsm_dlci_release(dlci[B]) ----- | | gsm_dlci_free(dlci[B]) ----- | | ----- gsmtty_open(gsmttyB) gsmtty_open() { struct gsm_dlci *dlci = tty->driver_data; => here it uses dlci[B] ... } In gsmtty_open(gsmttyA), it uses dlci[B] which was release, so hit a panic. ===================================================================== CASE #2 ===================================================================== releasing dlci[0] race with gsmtty_install(gsmttyB), then panic in gsmtty_open(), as below: tty_release(ttyA) tty_open(gsmttyB) | | ----- gsmtty_install(gsmttyB) | | ----- gsm_dlci_alloc(gsmttyB) => alloc dlci[B] | | ----- gsmtty_open(gsmttyB) fail | | ----- tty_release(gsmttyB) | | ----- gsmtty_close(gsmttyB) | | ----- gsmtty_detach_dlci(dlci[B]) | | ----- dlci_put(dlci[B]) | | tty_ldisc_release(ttyA) ----- | | gsm_dlci_release(dlci[0]) ----- | | gsm_dlci_free(dlci[0]) ----- | | ----- dlci_put(dlci[0]) In gsmtty_detach_dlci(dlci[B]), it tries to use dlci[0] which was released, then hit panic. ===================================================================== IMHO, n_gsm tty operations would refer released ldisc, as long as gsm_dlci_release() has chance to release ldisc data when some gsmtty operations are not completed.. This patch is try to avoid it by: 1) in n_gsm driver, use a global gsm spin lock to avoid gsm_dlci_release() run in parallel with gsmtty_install(); 2) Increase dlci's ref count in gsmtty_install() instead of in gsmtty_open(), the purpose is to prevent gsm_dlci_release() releasing dlci after gsmtty_install() allocats dlci but before gsmtty_open increases dlci's ref count; 3) Decrease dlci's ref count in gsmtty_remove(), which is a tty framework api, and this is the opposite process of step 2). Signed-off-by: Chao Bi Signed-off-by: Greg Kroah-Hartman --- drivers/tty/n_gsm.c | 37 +++++++++++++++++++++++++++---------- 1 file changed, 27 insertions(+), 10 deletions(-) diff --git a/drivers/tty/n_gsm.c b/drivers/tty/n_gsm.c index c0f76da5530..069bfd65448 100644 --- a/drivers/tty/n_gsm.c +++ b/drivers/tty/n_gsm.c @@ -2054,9 +2054,11 @@ void gsm_cleanup_mux(struct gsm_mux *gsm) dlci->state == DLCI_CLOSED); } /* Free up any link layer users */ + spin_lock(&gsm->lock); for (i = 0; i < NUM_DLCI; i++) if (gsm->dlci[i]) gsm_dlci_release(gsm->dlci[i]); + spin_unlock(&gsm->lock); /* Now wipe the queues */ list_for_each_entry_safe(txq, ntxq, &gsm->tx_list, list) kfree(txq); @@ -2909,23 +2911,33 @@ static int gsmtty_install(struct tty_driver *driver, struct tty_struct *tty) This is ok from a locking perspective as we don't have to worry about this if DLCI0 is lost */ - if (gsm->dlci[0] && gsm->dlci[0]->state != DLCI_OPEN) + spin_lock(&gsm->lock); + if (gsm->dlci[0] && gsm->dlci[0]->state != DLCI_OPEN) { + spin_unlock(&gsm->lock); return -EL2NSYNC; + } dlci = gsm->dlci[line]; if (dlci == NULL) { alloc = true; dlci = gsm_dlci_alloc(gsm, line); } - if (dlci == NULL) + if (dlci == NULL) { + spin_unlock(&gsm->lock); return -ENOMEM; + } ret = tty_port_install(&dlci->port, driver, tty); if (ret) { if (alloc) dlci_put(dlci); + spin_unlock(&gsm->lock); return ret; } + dlci_get(dlci); + dlci_get(gsm->dlci[0]); + mux_get(gsm); tty->driver_data = dlci; + spin_unlock(&gsm->lock); return 0; } @@ -2936,9 +2948,6 @@ static int gsmtty_open(struct tty_struct *tty, struct file *filp) struct tty_port *port = &dlci->port; port->count++; - dlci_get(dlci); - dlci_get(dlci->gsm->dlci[0]); - mux_get(dlci->gsm); tty_port_tty_set(port, tty); dlci->modem_rx = 0; @@ -2965,7 +2974,7 @@ static void gsmtty_close(struct tty_struct *tty, struct file *filp) mutex_unlock(&dlci->mutex); gsm = dlci->gsm; if (tty_port_close_start(&dlci->port, tty, filp) == 0) - goto out; + return; gsm_dlci_begin_close(dlci); if (test_bit(ASYNCB_INITIALIZED, &dlci->port.flags)) { if (C_HUPCL(tty)) @@ -2973,10 +2982,7 @@ static void gsmtty_close(struct tty_struct *tty, struct file *filp) } tty_port_close_end(&dlci->port, tty); tty_port_tty_set(&dlci->port, NULL); -out: - dlci_put(dlci); - dlci_put(gsm->dlci[0]); - mux_put(gsm); + return; } static void gsmtty_hangup(struct tty_struct *tty) @@ -3153,6 +3159,16 @@ static int gsmtty_break_ctl(struct tty_struct *tty, int state) return gsmtty_modem_update(dlci, encode); } +static void gsmtty_remove(struct tty_driver *driver, struct tty_struct *tty) +{ + struct gsm_dlci *dlci = tty->driver_data; + struct gsm_mux *gsm = dlci->gsm; + + dlci_put(dlci); + dlci_put(gsm->dlci[0]); + mux_put(gsm); + driver->ttys[tty->index] = NULL; +} /* Virtual ttys for the demux */ static const struct tty_operations gsmtty_ops = { @@ -3172,6 +3188,7 @@ static const struct tty_operations gsmtty_ops = { .tiocmget = gsmtty_tiocmget, .tiocmset = gsmtty_tiocmset, .break_ctl = gsmtty_break_ctl, + .remove = gsmtty_remove, }; -- 2.41.0