From 7dd2dd4ff9f3abda601f22b9d01441a0869d20d7 Mon Sep 17 00:00:00 2001
From: Adrian Larumbe <adrian.martinezlarumbe@imgtec.com>
Date: Wed, 7 Jul 2021 00:43:38 +0100
Subject: [PATCH] dmaengine: xilinx_dma: Fix read-after-free bug when terminating transfers
Git-commit: 7dd2dd4ff9f3abda601f22b9d01441a0869d20d7
Patch-mainline: v5.14-rc5
References: git-fixes

When user calls dmaengine_terminate_sync, the driver will clean up any
remaining descriptors for all the pending or active transfers that had
previously been submitted. However, this might happen whilst the tasklet is
invoking the DMA callback for the last finished transfer, so by the time it
returns and takes over the channel's spinlock, the list of completed
descriptors it was traversing is no longer valid. This leads to a
read-after-free situation.

Fix it by signalling whether a user-triggered termination has happened by
means of a boolean variable.

Signed-off-by: Adrian Larumbe <adrian.martinezlarumbe@imgtec.com>
Link: https://lore.kernel.org/r/20210706234338.7696-3-adrian.martinezlarumbe@imgtec.com
Signed-off-by: Vinod Koul <vkoul@kernel.org>
Acked-by: Takashi Iwai <tiwai@suse.de>

---
 drivers/dma/xilinx/xilinx_dma.c |   12 ++++++++++++
 1 file changed, 12 insertions(+)

--- a/drivers/dma/xilinx/xilinx_dma.c
+++ b/drivers/dma/xilinx/xilinx_dma.c
@@ -333,6 +333,7 @@ struct xilinx_dma_tx_descriptor {
  * @genlock: Support genlock mode
  * @err: Channel has errors
  * @idle: Check for channel idle
+ * @terminating: Check for channel being synchronized by user
  * @tasklet: Cleanup work after irq
  * @config: Device configuration info
  * @flush_on_fsync: Flush on Frame sync
@@ -370,6 +371,7 @@ struct xilinx_dma_chan {
 	bool genlock;
 	bool err;
 	bool idle;
+	bool terminating;
 	struct tasklet_struct tasklet;
 	struct xilinx_vdma_config config;
 	bool flush_on_fsync;
@@ -844,6 +846,13 @@ static void xilinx_dma_chan_desc_cleanup
 		/* Run any dependencies, then free the descriptor */
 		dma_run_dependencies(&desc->async_tx);
 		xilinx_dma_free_tx_descriptor(chan, desc);
+
+		/*
+		 * While we ran a callback the user called a terminate function,
+		 * which takes care of cleaning up any remaining descriptors
+		 */
+		if (chan->terminating)
+			break;
 	}
 
 	spin_unlock_irqrestore(&chan->lock, flags);
@@ -1618,6 +1627,8 @@ static dma_cookie_t xilinx_dma_tx_submit
 	if (desc->cyclic)
 		chan->cyclic = true;
 
+	chan->terminating = false;
+
 	spin_unlock_irqrestore(&chan->lock, flags);
 
 	return cookie;
@@ -2074,6 +2085,7 @@ static int xilinx_dma_terminate_all(stru
 	}
 
 	/* Remove and free all of the descriptors in the lists */
+	chan->terminating = true;
 	xilinx_dma_free_descriptors(chan);
 	chan->idle = true;