[ 003/123] firmware loader: Fix the concurrent request_firmware() race for kref_get/put

Greg Kroah-Hartman
2013-01-09T20:36:56Z

From: Chuansheng Liu <chuansheng.liu@intel.com>

commit bd9eb7fbe69111ea0ff1f999ef4a5f26d223d1d5 upstream.

There is one race that both request_firmware() with the same
firmware name.

The race scenerio is as below:
CPU1 CPU2
request_firmware() -->
_request_firmware_load() return err another request_firmware() is coming -->
_request_firmware_cleanup is called --> _request_firmware_prepare -->
release_firmware ---> fw_lookup_and_allocate_buf -->
spin_lock(&fwc->lock)
... __fw_lookup_buf() return true
fw_free_buf() will be called --> ...
kref_put -->
decrease the refcount to 0
kref_get(&tmp->ref) ==> it will trigger warning
due to refcount == 0
__fw_free_buf() -->
... spin_unlock(&fwc->lock)
spin_lock(&fwc->lock)
list_del(&buf->list)
spin_unlock(&fwc->lock)
kfree(buf)
After that, the freed buf will be used.

The key race is decreasing refcount to 0 and list_del is not protected together by
fwc->lock, and it is possible another thread try to get it between refcount==0
and list_del.

Fix it here to protect it together.

Acked-by: Ming Lei <ming.lei@canonical.com>
Signed-off-by: liu chuansheng <chuansheng.liu@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
drivers/base/firmware_class.c | 6 ++++--
1 file changed, 4 insertions(+), 2 deletions(-)

--- a/drivers/base/firmware_class.c
+++ b/drivers/base/firmware_class.c
@@ -246,7 +246,6 @@ static void __fw_free_buf(struct kref *r
__func__, buf->fw_id, buf, buf->data,
(unsigned int)buf->size);

- spin_lock(&fwc->lock);
list_del(&buf->list);
spin_unlock(&fwc->lock);

@@ -263,7 +262,10 @@ static void __fw_free_buf(struct kref *r

static void fw_free_buf(struct firmware_buf *buf)
{
- kref_put(&buf->ref, __fw_free_buf);
+ struct firmware_cache *fwc = buf->fwc;
+ spin_lock(&fwc->lock);
+ if (!kref_put(&buf->ref, __fw_free_buf))
+ spin_unlock(&fwc->lock);
}

/* direct firmware loading support */