The ION_IOC_{MAP,SHARE} ioctls drop and reacquire client->lock several times while operating on one of the client's ion_handles. This creates windows where userspace can call ION_IOC_FREE on the same client with the same handle, and effectively make the kernel drop its own reference. For example:

- thread A: ION_IOC_ALLOC creates an ion_handle with refcount 1 - thread A: starts ION_IOC_MAP and increments the refcount to 2 - thread B: ION_IOC_FREE decrements the refcount to 1 - thread B: ION_IOC_FREE decrements the refcount to 0 and frees the handle - thread A: continues ION_IOC_MAP with a dangling ion_handle * to freed memory

Fix this by holding client->lock for the duration of ION_IOC_{MAP,SHARE}, preventing the concurrent ION_IOC_FREE. Also remove ion_handle_get_by_id(), since there's literally no way to use it safely.

This patch is applied on top of 4.9.y. Kernels 4.12 and later are unaffected, since all the underlying ion_handle infrastructure has been ripped out.

Cc: stable@vger.kernel.org # v4.11- Signed-off-by: Greg Hackmann ghackmann@google.com --- drivers/staging/android/ion/ion-ioctl.c | 12 ++++--- drivers/staging/android/ion/ion.c | 48 +++++++++++++++---------- drivers/staging/android/ion/ion_priv.h | 6 ++-- 3 files changed, 40 insertions(+), 26 deletions(-)

diff --git a/drivers/staging/android/ion/ion-ioctl.c b/drivers/staging/android/ion/ion-ioctl.c index 2b700e8455c6..e3596855a703 100644 --- a/drivers/staging/android/ion/ion-ioctl.c +++ b/drivers/staging/android/ion/ion-ioctl.c @@ -128,11 +128,15 @@ long ion_ioctl(struct file *filp, unsigned int cmd, unsigned long arg) { struct ion_handle *handle;

- handle = ion_handle_get_by_id(client, data.handle.handle); - if (IS_ERR(handle)) + mutex_lock(&client->lock); + handle = ion_handle_get_by_id_nolock(client, data.handle.handle); + if (IS_ERR(handle)) { + mutex_unlock(&client->lock); return PTR_ERR(handle); - data.fd.fd = ion_share_dma_buf_fd(client, handle); - ion_handle_put(handle); + } + data.fd.fd = ion_share_dma_buf_fd_nolock(client, handle); + ion_handle_put_nolock(handle); + mutex_unlock(&client->lock); if (data.fd.fd < 0) ret = data.fd.fd; break; diff --git a/drivers/staging/android/ion/ion.c b/drivers/staging/android/ion/ion.c index 6f9974cb0e15..403df8bf4b48 100644 --- a/drivers/staging/android/ion/ion.c +++ b/drivers/staging/android/ion/ion.c @@ -352,18 +352,6 @@ struct ion_handle *ion_handle_get_by_id_nolock(struct ion_client *client, return handle ? handle : ERR_PTR(-EINVAL); }

-struct ion_handle *ion_handle_get_by_id(struct ion_client *client, - int id) -{ - struct ion_handle *handle; - - mutex_lock(&client->lock); - handle = ion_handle_get_by_id_nolock(client, id); - mutex_unlock(&client->lock); - - return handle; -} - static bool ion_handle_validate(struct ion_client *client, struct ion_handle *handle) { @@ -1029,24 +1017,28 @@ static struct dma_buf_ops dma_buf_ops = { .kunmap = ion_dma_buf_kunmap, };

-struct dma_buf *ion_share_dma_buf(struct ion_client *client, - struct ion_handle *handle) +static struct dma_buf *__ion_share_dma_buf(struct ion_client *client, + struct ion_handle *handle, + bool lock_client) { DEFINE_DMA_BUF_EXPORT_INFO(exp_info); struct ion_buffer *buffer; struct dma_buf *dmabuf; bool valid_handle;

- mutex_lock(&client->lock); + if (lock_client) + mutex_lock(&client->lock); valid_handle = ion_handle_validate(client, handle); if (!valid_handle) { WARN(1, "%s: invalid handle passed to share.\n", __func__); - mutex_unlock(&client->lock); + if (lock_client) + mutex_unlock(&client->lock); return ERR_PTR(-EINVAL); } buffer = handle->buffer; ion_buffer_get(buffer); - mutex_unlock(&client->lock); + if (lock_client) + mutex_unlock(&client->lock);

exp_info.ops = &dma_buf_ops; exp_info.size = buffer->size; @@ -1061,14 +1053,21 @@ struct dma_buf *ion_share_dma_buf(struct ion_client *client,

return dmabuf; } + +struct dma_buf *ion_share_dma_buf(struct ion_client *client, + struct ion_handle *handle) +{ + return __ion_share_dma_buf(client, handle, true); +} EXPORT_SYMBOL(ion_share_dma_buf);

-int ion_share_dma_buf_fd(struct ion_client *client, struct ion_handle *handle) +static int __ion_share_dma_buf_fd(struct ion_client *client, + struct ion_handle *handle, bool lock_client) { struct dma_buf *dmabuf; int fd;

- dmabuf = ion_share_dma_buf(client, handle); + dmabuf = __ion_share_dma_buf(client, handle, lock_client); if (IS_ERR(dmabuf)) return PTR_ERR(dmabuf);

@@ -1078,8 +1077,19 @@ int ion_share_dma_buf_fd(struct ion_client *client, struct ion_handle *handle)

return fd; } + +int ion_share_dma_buf_fd(struct ion_client *client, struct ion_handle *handle) +{ + return __ion_share_dma_buf_fd(client, handle, true); +} EXPORT_SYMBOL(ion_share_dma_buf_fd);

+int ion_share_dma_buf_fd_nolock(struct ion_client *client, + struct ion_handle *handle) +{ + return __ion_share_dma_buf_fd(client, handle, false); +} + struct ion_handle *ion_import_dma_buf(struct ion_client *client, struct dma_buf *dmabuf) { diff --git a/drivers/staging/android/ion/ion_priv.h b/drivers/staging/android/ion/ion_priv.h index 3c3b3245275d..760e41885448 100644 --- a/drivers/staging/android/ion/ion_priv.h +++ b/drivers/staging/android/ion/ion_priv.h @@ -463,11 +463,11 @@ void ion_free_nolock(struct ion_client *client, struct ion_handle *handle);

int ion_handle_put_nolock(struct ion_handle *handle);

-struct ion_handle *ion_handle_get_by_id(struct ion_client *client, - int id); - int ion_handle_put(struct ion_handle *handle);

int ion_query_heaps(struct ion_client *client, struct ion_heap_query *query);

+int ion_share_dma_buf_fd_nolock(struct ion_client *client, + struct ion_handle *handle); + #endif /* _ION_PRIV_H */