dmaengine: fix use-after-free in dma_chan_put() and dma_release_channel()grafted

When dma_device_put() drops the last reference on chan->device->ref,
dma_device_release() runs and may free the dma_device along with its
channels.

dma_chan_put() then still reads chan->device->owner via
dma_chan_to_owner() for the trailing module_put(). KASAN catches it:

	slab-use-after-free in dma_chan_put+0x3e6/0x4c0
	Read of size 8 by task insmod/6319
	Freed by task 6319:
	  kfree+0x225/0x470
	  dma_chan_put+0x395/0x4c0
	  dmaengine_put+0xf8/0x160

Cache the module owner in dma_chan_put() before the put so the trailing
module_put() does not need chan->device.

Fixes: 8ad342a86359 ("dmaengine: Add reference counting to dma_device struct")
Suggested-by: Sashiko <sashiko-bot@kernel.org>
Link: https://sashiko.dev/#/patchset/20260518-dmaengine-kref-fix-v1-1-4d6125048fb7@amd.com
Reviewed-by: Frank Li <Frank.Li@nxp.com>
Reviewed-by: Logan Gunthorpe <logang@deltatee.com>
Signed-off-by: Shivank Garg <shivankg@amd.com>
Link: https://patch.msgid.link/20260822-dmaengine-kref-fix-v5-3-d4a4ee47d927@amd.com
Signed-off-by: Vinod Koul <vkoul@kernel.org>

1 files changed, 88 insertions, 0 deletions

diff --git a/drivers/md/dm-cache-background-tracker.h b/drivers/md/dm-cache-background-tracker.h
new file mode 100644
index 000000000..47156c14a
--- /dev/null
+++ b/drivers/md/dm-cache-background-tracker.h
@@ -0,0 +1,88 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+/*
+ * Copyright (C) 2017 Red Hat. All rights reserved.
+ *
+ * This file is released under the GPL.
+ */
+
+#ifndef DM_CACHE_BACKGROUND_WORK_H
+#define DM_CACHE_BACKGROUND_WORK_H
+
+#include <linux/vmalloc.h>
+#include "dm-cache-policy.h"
+
+/*----------------------------------------------------------------*/
+
+/*
+ * The cache policy decides what background work should be performed,
+ * such as promotions, demotions and writebacks. The core cache target
+ * is in charge of performing the work, and does so when it sees fit.
+ *
+ * The background_tracker acts as a go between. Keeping track of future
+ * work that the policy has decided upon, and handing (issuing) it to
+ * the core target when requested.
+ *
+ * There is no locking in this, so calls will probably need to be
+ * protected with a spinlock.
+ */
+
+struct bt_work {
+	struct list_head list;
+	struct rb_node node;
+	struct policy_work work;
+};
+
+extern struct kmem_cache *btracker_work_cache;
+
+struct background_work;
+struct background_tracker;
+
+/*
+ * Create a new tracker, it will not be able to queue more than
+ * 'max_work' entries.
+ */
+struct background_tracker *btracker_create(unsigned int max_work);
+
+/*
+ * Destroy the tracker. No issued, but not complete, work should
+ * exist when this is called. It is fine to have queued but unissued
+ * work.
+ */
+void btracker_destroy(struct background_tracker *b);
+
+unsigned int btracker_nr_demotions_queued(struct background_tracker *b);
+
+/*
+ * Queue some work within the tracker. 'work' should point to the work
+ * to queue, this will be copied (ownership doesn't pass).  If pwork
+ * is not NULL then it will be set to point to the tracker's internal
+ * copy of the work.
+ *
+ * returns -EINVAL iff the work is already queued.  -ENOMEM if the work
+ * couldn't be queued for another reason.
+ */
+int btracker_queue(struct background_tracker *b,
+		   struct policy_work *work,
+		   struct policy_work **pwork);
+
+/*
+ * Hands out the next piece of work to be performed.
+ * Returns -ENODATA if there's no work.
+ */
+int btracker_issue(struct background_tracker *b, struct policy_work **work);
+
+/*
+ * Informs the tracker that the work has been completed and it may forget
+ * about it.
+ */
+void btracker_complete(struct background_tracker *b, struct policy_work *op);
+
+/*
+ * Predicate to see if an origin block is already scheduled for promotion.
+ */
+bool btracker_promotion_already_present(struct background_tracker *b,
+					dm_oblock_t oblock);
+
+/*----------------------------------------------------------------*/
+
+#endif