Hi Greg,
I think there is a race between usb_serial_put() and
usb_serial_get_by_index() (and get_free_serial()) with regards
to handling the serial port refcount.
usb_serial_get_by_index() gets a reference on the serial port under
table_lock while return_serial releases all the returned ports
from the table under the same lock. However, the table_lock is not
taken around the call to kref_put, theoretically allowing to sneak
in and grab a reference after kref_put has already determined that
the reference count is zero (and before calling destroy_serial)
causing use after free.
How about this fix?
>From b91b9cffd8bbb727c6480dfb18f79655806237e6 Mon Sep 17 00:00:00 2001
From: Benny Halevy <[email protected]>
Date: Tue, 15 May 2007 10:41:31 +0300
Subject: [PATCH] fix usb_serial_put synchronization
Signed-off-by: Benny Halevy <[email protected]>
---
drivers/usb/serial/usb-serial.c | 4 ++--
1 files changed, 2 insertions(+), 2 deletions(-)
diff --git a/drivers/usb/serial/usb-serial.c b/drivers/usb/serial/usb-serial.c
index 87f3788..4e5b996 100644
--- a/drivers/usb/serial/usb-serial.c
+++ b/drivers/usb/serial/usb-serial.c
@@ -120,11 +120,9 @@ static void return_serial(struct usb_serial *serial)
if (serial == NULL)
return;
- spin_lock(&table_lock);
for (i = 0; i < serial->num_ports; ++i) {
serial_table[serial->minor + i] = NULL;
}
- spin_unlock(&table_lock);
}
static void destroy_serial(struct kref *kref)
@@ -172,7 +170,9 @@ static void destroy_serial(struct kref *kref)
void usb_serial_put(struct usb_serial *serial)
{
+ spin_lock(&table_lock);
kref_put(&serial->kref, destroy_serial);
+ spin_unlock(&table_lock);
}
/*****************************************************************************
-
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