firmware loader: fix use-after-free by double abort

fw_priv->buf is accessed in both request_firmware_load() and
writing to sysfs file of 'loading' context, but not protected
by 'fw_lock' entirely. The patch makes sure that access on
'fw_priv->buf' is protected by the lock.

So fixes the double abort problem reported by nirinA raseliarison:

	http://lkml.org/lkml/2013/6/14/188

Reported-and-tested-by: nirinA raseliarison <nirina.raseliarison@gmail.com>
Cc: Guenter Roeck <linux@roeck-us.net>
Cc: Bjorn Helgaas <bhelgaas@google.com>
Cc: stable <stable@vger.kernel.org> # 3.9
Signed-off-by: Ming Lei <ming.lei@canonical.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

1 files changed, 18 insertions, 9 deletions

diff --git a/drivers/base/firmware_class.c b/drivers/base/firmware_class.c
index 4b1f9265887f..01e21037d8fe 100644
--- a/drivers/base/firmware_class.c
+++ b/drivers/base/firmware_class.c
@@ -450,8 +450,18 @@ static void fw_load_abort(struct firmware_priv *fw_priv)
 {
         struct firmware_buf *buf = fw_priv->buf;
 
+        /*
+         * There is a small window in which user can write to 'loading'
+         * between loading done and disappearance of 'loading'
+         */
+        if (test_bit(FW_STATUS_DONE, &buf->status))
+                return;
+
         set_bit(FW_STATUS_ABORT, &buf->status);
         complete_all(&buf->completion);
+
+        /* avoid user action after loading abort */
+        fw_priv->buf = NULL;
 }
 
 #define is_fw_load_aborted(buf) \
@@ -528,7 +538,12 @@ static ssize_t firmware_loading_show(struct device *dev,
                                      struct device_attribute *attr, char *buf)
 {
         struct firmware_priv *fw_priv = to_firmware_priv(dev);
-        int loading = test_bit(FW_STATUS_LOADING, &fw_priv->buf->status);
+        int loading = 0;
+
+        mutex_lock(&fw_lock);
+        if (fw_priv->buf)
+                loading = test_bit(FW_STATUS_LOADING, &fw_priv->buf->status);
+        mutex_unlock(&fw_lock);
 
         return sprintf(buf, "%d\n", loading);
 }
@@ -570,12 +585,12 @@ static ssize_t firmware_loading_store(struct device *dev,
                                       const char *buf, size_t count)
 {
         struct firmware_priv *fw_priv = to_firmware_priv(dev);
-        struct firmware_buf *fw_buf = fw_priv->buf;
+        struct firmware_buf *fw_buf;
         int loading = simple_strtol(buf, NULL, 10);
         int i;
 
         mutex_lock(&fw_lock);
-
+        fw_buf = fw_priv->buf;
         if (!fw_buf)
                 goto out;
 
@@ -777,10 +792,6 @@ static void firmware_class_timeout_work(struct work_struct *work)
                         struct firmware_priv, timeout_work.work);
 
         mutex_lock(&fw_lock);
-        if (test_bit(FW_STATUS_DONE, &(fw_priv->buf->status))) {
-                mutex_unlock(&fw_lock);
-                return;
-        }
         fw_load_abort(fw_priv);
         mutex_unlock(&fw_lock);
 }
@@ -861,8 +872,6 @@ static int _request_firmware_load(struct firmware_priv *fw_priv, bool uevent,
 
         cancel_delayed_work_sync(&fw_priv->timeout_work);
 
-        fw_priv->buf = NULL;
-
         device_remove_file(f_dev, &dev_attr_loading);
 err_del_bin_attr:
         device_remove_bin_file(f_dev, &firmware_attr_data);