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, 61 insertions, 0 deletions

diff --git a/drivers/md/dm-pcache/segment.c b/drivers/md/dm-pcache/segment.c
new file mode 100644
index 000000000..8f8816e1c
--- /dev/null
+++ b/drivers/md/dm-pcache/segment.c
@@ -0,0 +1,61 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+#include <linux/dax.h>
+
+#include "pcache_internal.h"
+#include "cache_dev.h"
+#include "segment.h"
+
+int segment_copy_to_bio(struct pcache_segment *segment,
+		u32 data_off, u32 data_len, struct bio *bio, u32 bio_off)
+{
+	struct iov_iter iter;
+	size_t copied;
+	void *src;
+
+	iov_iter_bvec(&iter, ITER_DEST, &bio->bi_io_vec[bio->bi_iter.bi_idx],
+			bio_segments(bio), bio->bi_iter.bi_size);
+	iter.iov_offset = bio->bi_iter.bi_offset;
+	if (bio_off)
+		iov_iter_advance(&iter, bio_off);
+
+	src = segment->data + data_off;
+	copied = _copy_mc_to_iter(src, data_len, &iter);
+	if (copied != data_len)
+		return -EIO;
+
+	return 0;
+}
+
+int segment_copy_from_bio(struct pcache_segment *segment,
+		u32 data_off, u32 data_len, struct bio *bio, u32 bio_off)
+{
+	struct iov_iter iter;
+	size_t copied;
+	void *dst;
+
+	iov_iter_bvec(&iter, ITER_SOURCE, &bio->bi_io_vec[bio->bi_iter.bi_idx],
+			bio_segments(bio), bio->bi_iter.bi_size);
+	iter.iov_offset = bio->bi_iter.bi_offset;
+	if (bio_off)
+		iov_iter_advance(&iter, bio_off);
+
+	dst = segment->data + data_off;
+	copied = _copy_from_iter_flushcache(dst, data_len, &iter);
+	if (copied != data_len)
+		return -EIO;
+	pmem_wmb();
+
+	return 0;
+}
+
+void pcache_segment_init(struct pcache_cache_dev *cache_dev, struct pcache_segment *segment,
+		      struct pcache_segment_init_options *options)
+{
+	segment->seg_info = options->seg_info;
+	segment_info_set_type(segment->seg_info, options->type);
+
+	segment->cache_dev = cache_dev;
+	segment->seg_id = options->seg_id;
+	segment->data_size = PCACHE_SEG_SIZE - options->data_off;
+	segment->data = CACHE_DEV_SEGMENT(cache_dev, options->seg_id) + options->data_off;
+}