[PATCH v4 1/4] dmaengine: Fix possible use after free

[Nuno Sá via B4 Relay]

From: Nuno Sá <nuno.sa@xxxxxxxxxx>

In dma_release_channel(), check chan->device->privatecnt after call
dma_chan_put(). However, dma_chan_put() call dma_device_put() which could
release the last reference of the device if the DMA provider is already
gone and hence free it.

Fixes it by moving dma_chan_put() after the check.

Fixes: 0f571515c332 ("dmaengine: Add privatecnt to revert DMA_PRIVATE property")
Signed-off-by: Nuno Sá <nuno.sa@xxxxxxxxxx>
---
 drivers/dma/dmaengine.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/dma/dmaengine.c b/drivers/dma/dmaengine.c
index 405bd2fbb4a3..9049171df857 100644
--- a/drivers/dma/dmaengine.c
+++ b/drivers/dma/dmaengine.c
@@ -905,11 +905,12 @@ void dma_release_channel(struct dma_chan *chan)
 	mutex_lock(&dma_list_mutex);
 	WARN_ONCE(chan->client_count != 1,
 		  "chan reference count %d != 1\n", chan->client_count);
-	dma_chan_put(chan);
 	/* drop PRIVATE cap enabled by __dma_request_channel() */
 	if (--chan->device->privatecnt == 0)
 		dma_cap_clear(DMA_PRIVATE, chan->device->cap_mask);
 
+	dma_chan_put(chan);
+
 	if (chan->slave) {
 		sysfs_remove_link(&chan->dev->device.kobj, DMA_SLAVE_NAME);
 		sysfs_remove_link(&chan->slave->kobj, chan->name);

-- 
2.54.0