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tee: handle lookup of shm with reference count 0

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commit dfd0743f1d9ea76931510ed150334d571fbab49d upstream.

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: 967c9cca2c ("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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Jens Wiklander
2021-12-09 15:59:37 +01:00
committed by Greg Kroah-Hartman
parent 0ffb9f83e4
commit c05d8f66ec
2 changed files with 68 additions and 107 deletions
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4
include/linux/tee_drv.h
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@@ -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
*
@@ -210,7 +210,7 @@ struct tee_shm {
unsigned int offset;
struct page **pages;
size_t num_pages;
struct dma_buf *dmabuf;
refcount_t refcount;
u32 flags;
int id;
};