[PATCH AUTOSEL 4.19 39/65] staging: android: ion: Support cpu access during dma_buf_detach

[Sasha Levin]

From: Liam Mark <lmark at codeaurora.org>

[ Upstream commit 31eb79db420a3f94c4c45a8c0a05cd30e333f981 ]

Often userspace doesn't know when the kernel will be calling dma_buf_detach
on the buffer.
If userpace starts its CPU access at the same time as the sg list is being
freed it could end up accessing the sg list after it has been freed.

Thread A				Thread B
- DMA_BUF_IOCTL_SYNC IOCT
 - ion_dma_buf_begin_cpu_access
  - list_for_each_entry
					- ion_dma_buf_detatch
					 - free_duped_table
   - dma_sync_sg_for_cpu

Fix this by getting the ion_buffer lock before freeing the sg table memory.

Fixes: 2a55e7b5e544 ("staging: android: ion: Call dma_map_sg for syncing and mapping")
Signed-off-by: Liam Mark <lmark at codeaurora.org>
Acked-by: Laura Abbott <labbott at redhat.com>
Acked-by: Andrew F. Davis <afd at ti.com>
Signed-off-by: Greg Kroah-Hartman <gregkh at linuxfoundation.org>
Signed-off-by: Sasha Levin <sashal at kernel.org>
---
 drivers/staging/android/ion/ion.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/staging/android/ion/ion.c b/drivers/staging/android/ion/ion.c
index 99073325b0c0..45c7f829e387 100644
--- a/drivers/staging/android/ion/ion.c
+++ b/drivers/staging/android/ion/ion.c
@@ -237,10 +237,10 @@ static void ion_dma_buf_detatch(struct dma_buf *dmabuf,
 	struct ion_dma_buf_attachment *a = attachment->priv;
 	struct ion_buffer *buffer = dmabuf->priv;
 
-	free_duped_table(a->table);
 	mutex_lock(&buffer->lock);
 	list_del(&a->list);
 	mutex_unlock(&buffer->lock);
+	free_duped_table(a->table);
 
 	kfree(a);
 }
-- 
2.19.1