dma: ste_dma40: don't dereference free:d descriptor

It appears that in the DMA40 driver the DMA tasklet will very
often dereference memory for a descriptor just free:d from the
DMA40 slab. Nothing happens because no other part of the driver
has yet had a chance to claim this memory, but it's really
nasty to dereference free:d memory, so let's check the flag
before the descriptor is free and store it in a bool variable.

Cc: stable@vger.kernel.org
Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Vinod Koul <vinod.koul@intel.com>

1 files changed, 3 insertions, 1 deletions

diff --git a/drivers/dma/ste_dma40.c b/drivers/dma/ste_dma40.c
index 00a2de957b23..bf18c786ed40 100644
--- a/drivers/dma/ste_dma40.c
+++ b/drivers/dma/ste_dma40.c
@@ -1641,6 +1641,7 @@ static void dma_tasklet(unsigned long data)
         struct d40_chan *d40c = (struct d40_chan *) data;
         struct d40_desc *d40d;
         unsigned long flags;
+        bool callback_active;
         dma_async_tx_callback callback;
         void *callback_param;
 
@@ -1668,6 +1669,7 @@ static void dma_tasklet(unsigned long data)
         }
 
         /* Callback to client */
+        callback_active = !!(d40d->txd.flags & DMA_PREP_INTERRUPT);
         callback = d40d->txd.callback;
         callback_param = d40d->txd.callback_param;
 
@@ -1690,7 +1692,7 @@ static void dma_tasklet(unsigned long data)
 
         spin_unlock_irqrestore(&d40c->lock, flags);
 
-        if (callback && (d40d->txd.flags & DMA_PREP_INTERRUPT))
+        if (callback_active && callback)
                 callback(callback_param);
 
         return;