tee: handle lookup of shm with reference count 0

Since the tee subsystem does not keep a strong reference to its idle
shared memory buffers, it races with other threads that try to destroy a
shared memory through a close of its dma-buf fd or by unmapping the
memory.

In tee_shm_get_from_id() when a lookup in teedev->idr has been
successful, it is possible that the tee_shm is in the dma-buf teardown
path, but that path is blocked by the teedev mutex. Since we don't have
an API to tell if the tee_shm is in the dma-buf teardown path or not we
must find another way of detecting this condition.

Fix this by doing the reference counting directly on the tee_shm using a
new refcount_t refcount field. dma-buf is replaced by using
anon_inode_getfd() instead, this separates the life-cycle of the
underlying file from the tee_shm. tee_shm_put() is updated to hold the
mutex when decreasing the refcount to 0 and then remove the tee_shm from
teedev->idr before releasing the mutex. This means that the tee_shm can
never be found unless it has a refcount larger than 0.

Fixes: 967c9cca2cc5 ("tee: generic TEE subsystem")
Cc: stable@vger.kernel.org
Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Reviewed-by: Lars Persson <larper@axis.com>
Reviewed-by: Sumit Garg <sumit.garg@linaro.org>
Reported-by: Patrik Lantz <patrik.lantz@axis.com>
Signed-off-by: Jens Wiklander <jens.wiklander@linaro.org>

1 files changed, 2 insertions, 2 deletions

diff --git a/include/linux/tee_drv.h b/include/linux/tee_drv.h
index a1f03461369b..cf5999626e28 100644
--- a/include/linux/tee_drv.h
+++ b/include/linux/tee_drv.h
@@ -195,7 +195,7 @@ int tee_session_calc_client_uuid(uuid_t *uuid, u32 connection_method,
  * @offset:	offset of buffer in user space
  * @pages:	locked pages from userspace
  * @num_pages:	number of locked pages
- * @dmabuf:	dmabuf used to for exporting to user space
+ * @refcount:	reference counter
  * @flags:	defined by TEE_SHM_* in tee_drv.h
  * @id:		unique id of a shared memory object on this device, shared
  *		with user space
@@ -214,7 +214,7 @@ struct tee_shm {
 	unsigned int offset;
 	struct page **pages;
 	size_t num_pages;
-	struct dma_buf *dmabuf;
+	refcount_t refcount;
 	u32 flags;
 	int id;
 	u64 sec_world_id;