From 9590232bb4f4cc824f3425a6e1349afbe6d6d2b7 Mon Sep 17 00:00:00 2001 From: EunTaik Lee Date: Wed, 24 Feb 2016 04:38:06 +0000 Subject: [PATCH] staging/android/ion : fix a race condition in the ion driver There is a use-after-free problem in the ion driver. This is caused by a race condition in the ion_ioctl() function. A handle has ref count of 1 and two tasks on different cpus calls ION_IOC_FREE simultaneously. cpu 0 cpu 1 ------------------------------------------------------- ion_handle_get_by_id() (ref == 2) ion_handle_get_by_id() (ref == 3) ion_free() (ref == 2) ion_handle_put() (ref == 1) ion_free() (ref == 0 so ion_handle_destroy() is called and the handle is freed.) ion_handle_put() is called and it decreases the slub's next free pointer The problem is detected as an unaligned access in the spin lock functions since it uses load exclusive instruction. In some cases it corrupts the slub's free pointer which causes a mis-aligned access to the next free pointer.(kmalloc returns a pointer like ffffc0745b4580aa). And it causes lots of other hard-to-debug problems. This symptom is caused since the first member in the ion_handle structure is the reference count and the ion driver decrements the reference after it has been freed. To fix this problem client->lock mutex is extended to protect all the codes that uses the handle. Signed-off-by: Eun Taik Lee Reviewed-by: Laura Abbott Signed-off-by: Greg Kroah-Hartman --- drivers/staging/android/ion/ion.c | 59 +++++++++++++++++++++++-------- 1 file changed, 44 insertions(+), 15 deletions(-) mode change 100644 => 100755 drivers/staging/android/ion/ion.c diff --git a/drivers/staging/android/ion/ion.c b/drivers/staging/android/ion/ion.c old mode 100644 new mode 100755 index 7ff2a7ec871f..33b390e7ea31 --- a/drivers/staging/android/ion/ion.c +++ b/drivers/staging/android/ion/ion.c @@ -387,13 +387,22 @@ static void ion_handle_get(struct ion_handle *handle) kref_get(&handle->ref); } -static int ion_handle_put(struct ion_handle *handle) +static int ion_handle_put_nolock(struct ion_handle *handle) +{ + int ret; + + ret = kref_put(&handle->ref, ion_handle_destroy); + + return ret; +} + +int ion_handle_put(struct ion_handle *handle) { struct ion_client *client = handle->client; int ret; mutex_lock(&client->lock); - ret = kref_put(&handle->ref, ion_handle_destroy); + ret = ion_handle_put_nolock(handle); mutex_unlock(&client->lock); return ret; @@ -417,18 +426,28 @@ static struct ion_handle *ion_handle_lookup(struct ion_client *client, return ERR_PTR(-EINVAL); } -static struct ion_handle *ion_handle_get_by_id(struct ion_client *client, +static struct ion_handle *ion_handle_get_by_id_nolock(struct ion_client *client, + int id) +{ + struct ion_handle *handle; + + handle = idr_find(&client->idr, id); + if (handle) + ion_handle_get(handle); + + 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 = idr_find(&client->idr, id); - if (handle) - ion_handle_get(handle); + handle = ion_handle_get_by_id_nolock(client, id); mutex_unlock(&client->lock); - return handle ? handle : ERR_PTR(-EINVAL); + return handle; } static bool ion_handle_validate(struct ion_client *client, @@ -532,22 +551,28 @@ struct ion_handle *ion_alloc(struct ion_client *client, size_t len, } EXPORT_SYMBOL(ion_alloc); -void ion_free(struct ion_client *client, struct ion_handle *handle) +static void ion_free_nolock(struct ion_client *client, struct ion_handle *handle) { bool valid_handle; BUG_ON(client != handle->client); - mutex_lock(&client->lock); valid_handle = ion_handle_validate(client, handle); if (!valid_handle) { WARN(1, "%s: invalid handle passed to free.\n", __func__); - mutex_unlock(&client->lock); return; } + ion_handle_put_nolock(handle); +} + +void ion_free(struct ion_client *client, struct ion_handle *handle) +{ + BUG_ON(client != handle->client); + + mutex_lock(&client->lock); + ion_free_nolock(client, handle); mutex_unlock(&client->lock); - ion_handle_put(handle); } EXPORT_SYMBOL(ion_free); @@ -1332,11 +1357,15 @@ static 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); - ion_free(client, handle); - ion_handle_put(handle); + } + ion_free_nolock(client, handle); + ion_handle_put_nolock(handle); + mutex_unlock(&client->lock); break; } case ION_IOC_SHARE: