USB: prevent char device open/deregister race

This patch (as908) adds central protection in usbcore for the
prototypical race between opening and unregistering a char device.
The spinlock used to protect the minor-numbers array is replaced with
an rwsem, which can remain locked across a call to a driver's open()
method.  This guarantees that open() and deregister() will be mutually
exclusive.

The private locks currently used in several individual drivers for
this purpose are no longer necessary, and the patch removes them.  The
following USB drivers are affected: usblcd, idmouse, auerswald,
legousbtower, sisusbvga/sisusb, ldusb, adutux, iowarrior, and
usb-skeleton.

As a side effect of this change, usb_deregister_dev() must not be
called while holding a lock that is acquired by open().  Unfortunately
a number of drivers do this, but luckily the solution is simple: call
usb_deregister_dev() before acquiring the lock.

In addition to these changes (and their consequent code
simplifications), the patch fixes a use-after-free bug in adutux and a
race between open() and release() in iowarrior.

Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

1 files changed, 2 insertions, 23 deletions

diff --git a/drivers/usb/misc/sisusbvga/sisusb_con.c b/drivers/usb/misc/sisusbvga/sisusb_con.c
index 5947afb0017e..8d0edc867f33 100644
--- a/drivers/usb/misc/sisusbvga/sisusb_con.c
+++ b/drivers/usb/misc/sisusbvga/sisusb_con.c
@@ -214,18 +214,13 @@ sisusbcon_init(struct vc_data *c, int init)
 	 * are set up/restored.
 	 */
 
-	mutex_lock(&disconnect_mutex);
-
-	if (!(sisusb = sisusb_get_sisusb(c->vc_num))) {
-		mutex_unlock(&disconnect_mutex);
+	if (!(sisusb = sisusb_get_sisusb(c->vc_num)))
 		return;
-	}
 
 	mutex_lock(&sisusb->lock);
 
 	if (!sisusb_sisusb_valid(sisusb)) {
 		mutex_unlock(&sisusb->lock);
-		mutex_unlock(&disconnect_mutex);
 		return;
 	}
 
@@ -264,8 +259,6 @@ sisusbcon_init(struct vc_data *c, int init)
 
 	mutex_unlock(&sisusb->lock);
 
-	mutex_unlock(&disconnect_mutex);
-
 	if (init) {
 		c->vc_cols = cols;
 		c->vc_rows = rows;
@@ -284,12 +277,8 @@ sisusbcon_deinit(struct vc_data *c)
 	 * and others, ie not under our control.
 	 */
 
-	mutex_lock(&disconnect_mutex);
-
-	if (!(sisusb = sisusb_get_sisusb(c->vc_num))) {
-		mutex_unlock(&disconnect_mutex);
+	if (!(sisusb = sisusb_get_sisusb(c->vc_num)))
 		return;
-	}
 
 	mutex_lock(&sisusb->lock);
 
@@ -314,8 +303,6 @@ sisusbcon_deinit(struct vc_data *c)
 
 	/* decrement the usage count on our sisusb */
 	kref_put(&sisusb->kref, sisusb_delete);
-
-	mutex_unlock(&disconnect_mutex);
 }
 
 /* interface routine */
@@ -1490,14 +1477,11 @@ sisusb_console_init(struct sisusb_usb_data *sisusb, int first, int last)
 {
 	int i, ret, minor = sisusb->minor;
 
-	mutex_lock(&disconnect_mutex);
-
 	mutex_lock(&sisusb->lock);
 
 	/* Erm.. that should not happen */
 	if (sisusb->haveconsole || !sisusb->SiS_Pr) {
 		mutex_unlock(&sisusb->lock);
-		mutex_unlock(&disconnect_mutex);
 		return 1;
 	}
 
@@ -1508,14 +1492,12 @@ sisusb_console_init(struct sisusb_usb_data *sisusb, int first, int last)
 	    first > MAX_NR_CONSOLES ||
 	    last > MAX_NR_CONSOLES) {
 		mutex_unlock(&sisusb->lock);
-		mutex_unlock(&disconnect_mutex);
 		return 1;
 	}
 
 	/* If gfxcore not initialized or no consoles given, quit graciously */
 	if (!sisusb->gfxinit || first < 1 || last < 1) {
 		mutex_unlock(&sisusb->lock);
-		mutex_unlock(&disconnect_mutex);
 		return 0;
 	}
 
@@ -1526,7 +1508,6 @@ sisusb_console_init(struct sisusb_usb_data *sisusb, int first, int last)
 	/* Set up text mode (and upload  default font) */
 	if (sisusb_reset_text_mode(sisusb, 1)) {
 		mutex_unlock(&sisusb->lock);
-		mutex_unlock(&disconnect_mutex);
 		printk(KERN_ERR
 			"sisusbvga[%d]: Failed to set up text mode\n",
 			minor);
@@ -1550,7 +1531,6 @@ sisusb_console_init(struct sisusb_usb_data *sisusb, int first, int last)
 	/* Allocate screen buffer */
 	if (!(sisusb->scrbuf = (unsigned long)vmalloc(sisusb->scrbuf_size))) {
 		mutex_unlock(&sisusb->lock);
-		mutex_unlock(&disconnect_mutex);
 		printk(KERN_ERR
 			"sisusbvga[%d]: Failed to allocate screen buffer\n",
 			minor);
@@ -1558,7 +1538,6 @@ sisusb_console_init(struct sisusb_usb_data *sisusb, int first, int last)
 	}
 
 	mutex_unlock(&sisusb->lock);
-	mutex_unlock(&disconnect_mutex);
 
 	/* Now grab the desired console(s) */
 	ret = take_over_console(&sisusb_con, first - 1, last - 1, 0);