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, 31 insertions, 0 deletions

diff --git a/Documentation/admin-guide/blockdev/nbd.rst b/Documentation/admin-guide/blockdev/nbd.rst
new file mode 100644
index 000000000..faf2ac4b1
--- /dev/null
+++ b/Documentation/admin-guide/blockdev/nbd.rst
@@ -0,0 +1,31 @@
+==================================
+Network Block Device (TCP version)
+==================================
+
+1) Overview
+-----------
+
+What is it: With this compiled in the kernel (or as a module), Linux
+can use a remote server as one of its block devices. So every time
+the client computer wants to read, e.g., /dev/nb0, it sends a
+request over TCP to the server, which will reply with the data read.
+This can be used for stations with low disk space (or even diskless)
+to borrow disk space from another computer.
+Unlike NFS, it is possible to put any filesystem on it, etc.
+
+For more information, or to download the nbd-client and nbd-server
+tools, go to https://github.com/NetworkBlockDevice/nbd.
+
+The nbd kernel module need only be installed on the client
+system, as the nbd-server is completely in userspace. In fact,
+the nbd-server has been successfully ported to other operating
+systems, including Windows.
+
+A) NBD parameters
+-----------------
+
+max_part
+	Number of partitions per device (default: 0).
+
+nbds_max
+	Number of block devices that should be initialized (default: 16).