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 <eun.taik.lee@xxxxxxxxxxx>
---
changes in v2 :
1. add problem description in the comment
2. fix un-matching mutex_lock/unlock pair in ion_share_dma_buf()
drivers/staging/android/ion/ion.c | 102 ++++++++++++++++++++++++++++++--------
1 file changed, 82 insertions(+), 20 deletions(-)
diff --git a/drivers/staging/android/ion/ion.c b/drivers/staging/android/ion/ion.c
index e237e9f..c6fbe48 100644
--- a/drivers/staging/android/ion/ion.c
+++ b/drivers/staging/android/ion/ion.c
@@ -385,13 +385,22 @@ static void ion_handle_get(struct ion_handle *handle)
kref_get(&handle->ref);
}
+static int ion_handle_put_nolock(struct ion_handle *handle)
+{
+ int ret;
+
+ ret = kref_put(&handle->ref, ion_handle_destroy);
+
+ return ret;
+}
+
static 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;
@@ -415,20 +424,30 @@ 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,
- int id)
+static struct ion_handle *ion_handle_get_by_id_nolock(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);
- mutex_unlock(&client->lock);
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)
{
@@ -530,7 +549,8 @@ 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;
@@ -538,15 +558,24 @@ void ion_free(struct ion_client *client, struct ion_handle *handle)
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);
int ion_phys(struct ion_client *client, struct ion_handle *handle,
@@ -830,6 +859,7 @@ void ion_client_destroy(struct ion_client *client)
struct rb_node *n;
pr_debug("%s: %d\n", __func__, __LINE__);
+ mutex_lock(&client->lock);
while ((n = rb_first(&client->handles))) {
struct ion_handle *handle = rb_entry(n, struct ion_handle,
node);
@@ -837,6 +867,7 @@ void ion_client_destroy(struct ion_client *client)
}
idr_destroy(&client->idr);
+ mutex_unlock(&client->lock);
down_write(&dev->lock);
if (client->task)
@@ -1100,7 +1131,7 @@ static struct dma_buf_ops dma_buf_ops = {
.kunmap = ion_dma_buf_kunmap,
};
-struct dma_buf *ion_share_dma_buf(struct ion_client *client,
+static struct dma_buf *ion_share_dma_buf_nolock(struct ion_client *client,
struct ion_handle *handle)
{
DEFINE_DMA_BUF_EXPORT_INFO(exp_info);
@@ -1108,7 +1139,6 @@ struct dma_buf *ion_share_dma_buf(struct ion_client *client,
struct dma_buf *dmabuf;
bool valid_handle;
- mutex_lock(&client->lock);
valid_handle = ion_handle_validate(client, handle);
if (!valid_handle) {
WARN(1, "%s: invalid handle passed to share.\n", __func__);
@@ -1117,7 +1147,6 @@ struct dma_buf *ion_share_dma_buf(struct ion_client *client,
}
buffer = handle->buffer;
ion_buffer_get(buffer);
- mutex_unlock(&client->lock);
exp_info.ops = &dma_buf_ops;
exp_info.size = buffer->size;
@@ -1132,14 +1161,26 @@ 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)
+{
+ struct dma_buf *dmabuf;
+
+ mutex_lock(&client->lock);
+ dmabuf = ion_share_dma_buf_nolock(client, handle);
+ mutex_unlock(&client->lock);
+ return dmabuf;
+}
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_nolock(struct ion_client *client,
+ struct ion_handle *handle)
{
struct dma_buf *dmabuf;
int fd;
- dmabuf = ion_share_dma_buf(client, handle);
+ dmabuf = ion_share_dma_buf_nolock(client, handle);
if (IS_ERR(dmabuf))
return PTR_ERR(dmabuf);
@@ -1149,6 +1190,17 @@ 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)
+{
+ int fd;
+
+ mutex_lock(&client->lock);
+ fd = ion_share_dma_buf_fd_nolock(client, handle);
+ mutex_unlock(&client->lock);
+
+ return fd;
+}
EXPORT_SYMBOL(ion_share_dma_buf_fd);
struct ion_handle *ion_import_dma_buf(struct ion_client *client, int fd)
@@ -1281,11 +1333,16 @@ 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:
@@ -1293,11 +1350,16 @@ 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);
- 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;
--
1.9.1
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