linux-kernel - [PATCH 27/76] tty: use krefs to protect driver module counts

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20081005160820.1997.76436.stgit@localhost.localdomain>
Date:	Sun, 05 Oct 2008 17:08:23 +0100
From:	Alan Cox <alan@...hat.com>
To:	linux-kernel@...r.kernel.org
Subject: [PATCH 27/76] tty: use krefs to protect driver module counts

The tty layer keeps driver module counts that are used so the driver knows
when it can be unloaded. For obvious reasons we want to tie that to the
refcounting properly.

At this point the driver side itself isn't refcounted nicely but we can do
that later and kref the drivers.

Signed-off-by: Alan Cox <alan@...hat.com>
---

 drivers/char/tty_io.c |   17 +++++++++++------
 1 files changed, 11 insertions(+), 6 deletions(-)

diff --git a/drivers/char/tty_io.c b/drivers/char/tty_io.c
index 310e070..fa162c9 100644
--- a/drivers/char/tty_io.c
+++ b/drivers/char/tty_io.c
@@ -1293,6 +1293,12 @@ static int init_dev(struct tty_driver *driver, int idx,
 		o_tty = alloc_tty_struct();
 		if (!o_tty)
 			goto free_mem_out;
+		if (!try_module_get(driver->other->owner)) {
+			/* This cannot in fact currently happen */
+			free_tty_struct(o_tty);
+			o_tty = NULL;
+			goto free_mem_out;
+		}
 		initialize_tty_struct(o_tty);
 		o_tty->driver = driver->other;
 		o_tty->ops = driver->ops;
@@ -1411,8 +1417,10 @@ end_init:
 	/* Release locally allocated memory ... nothing placed in slots */
 free_mem_out:
 	kfree(o_tp);
-	if (o_tty)
+	if (o_tty) {
+		module_put(o_tty->driver->owner);
 		free_tty_struct(o_tty);
+	}
 	kfree(ltp);
 	kfree(tp);
 	free_tty_struct(tty);
@@ -1447,6 +1455,7 @@ release_mem_out:
 static void release_one_tty(struct kref *kref)
 {
 	struct tty_struct *tty = container_of(kref, struct tty_struct, kref);
+	struct tty_driver *driver = tty->driver;
 	int devpts = tty->driver->flags & TTY_DRIVER_DEVPTS_MEM;
 	struct ktermios *tp;
 	int idx = tty->index;
@@ -1471,6 +1480,7 @@ static void release_one_tty(struct kref *kref)
 	tty->magic = 0;
 	/* FIXME: locking on tty->driver->refcount */
 	tty->driver->refcount--;
+	module_put(driver->owner);
 
 	file_list_lock();
 	list_del_init(&tty->tty_files);
@@ -1506,20 +1516,15 @@ EXPORT_SYMBOL(tty_kref_put);
  *	of ttys that the driver keeps.
  *		FIXME: should we require tty_mutex is held here ??
  *
- *	FIXME: We want to defer the module put of the driver to the
- *	destructor.
  */
 static void release_tty(struct tty_struct *tty, int idx)
 {
-	struct tty_driver *driver = tty->driver;
-
 	/* This should always be true but check for the moment */
 	WARN_ON(tty->index != idx);
 
 	if (tty->link)
 		tty_kref_put(tty->link);
 	tty_kref_put(tty);
-	module_put(driver->owner);
 }
 
 /*

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/