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, 58 insertions, 0 deletions

diff --git a/Documentation/ABI/testing/sysfs-class-rnbd-server b/Documentation/ABI/testing/sysfs-class-rnbd-server
new file mode 100644
index 000000000..6c5996cd7
--- /dev/null
+++ b/Documentation/ABI/testing/sysfs-class-rnbd-server
@@ -0,0 +1,58 @@
+What:		/sys/class/rnbd-server
+Date:		Feb 2020
+KernelVersion:	5.7
+Contact:	Jack Wang <jinpu.wang@cloud.ionos.com> Danil Kipnis <danil.kipnis@cloud.ionos.com>
+Description:	provide information about RNBD-server.
+
+What:		/sys/class/rnbd-server/ctl/
+Date:		Feb 2020
+KernelVersion:	5.7
+Contact:	Jack Wang <jinpu.wang@cloud.ionos.com> Danil Kipnis <danil.kipnis@cloud.ionos.com>
+Description:	When a client maps a device, a directory entry with the name of the
+		block device is created under /sys/class/rnbd-server/ctl/devices/.
+
+What:		/sys/class/rnbd-server/ctl/devices/<device_name>/block_dev
+Date:		Feb 2020
+KernelVersion:	5.7
+Contact:	Jack Wang <jinpu.wang@cloud.ionos.com> Danil Kipnis <danil.kipnis@cloud.ionos.com>
+Description:	Is a symlink to the sysfs entry of the exported device.
+
+		Example:
+		block_dev -> ../../../../class/block/ram0
+
+What:		/sys/class/rnbd-server/ctl/devices/<device_name>/sessions/
+Date:		Feb 2020
+KernelVersion:	5.7
+Contact:	Jack Wang <jinpu.wang@cloud.ionos.com> Danil Kipnis <danil.kipnis@cloud.ionos.com>
+Description:	For each client a particular device is exported to, following directory will be
+		created:
+
+		/sys/class/rnbd-server/ctl/devices/<device_name>/sessions/<session-name>/
+
+		When the device is unmapped by that client, the directory will be removed.
+
+What:		/sys/class/rnbd-server/ctl/devices/<device_name>/sessions/<session-name>/read_only
+Date:		Feb 2020
+KernelVersion:	5.7
+Contact:	Jack Wang <jinpu.wang@cloud.ionos.com> Danil Kipnis <danil.kipnis@cloud.ionos.com>
+Description:	Contains '1' if device is mapped read-only, otherwise '0'.
+
+What:		/sys/class/rnbd-server/ctl/devices/<device_name>/sessions/<session-name>/mapping_path
+Date:		Feb 2020
+KernelVersion:	5.7
+Contact:	Jack Wang <jinpu.wang@cloud.ionos.com> Danil Kipnis <danil.kipnis@cloud.ionos.com>
+Description:	Contains the relative device path provided by the user during mapping.
+
+What:		/sys/class/rnbd-server/ctl/devices/<device_name>/sessions/<session-name>/access_mode
+Date:		Feb 2020
+KernelVersion:	5.7
+Contact:	Jack Wang <jinpu.wang@cloud.ionos.com> Danil Kipnis <danil.kipnis@cloud.ionos.com>
+Description:	Contains the device access mode: ro, rw or migration.
+
+What:		/sys/class/rnbd-server/ctl/devices/<device_name>/sessions/<session-name>/force_close
+Date:		Nov 2020
+KernelVersion:	5.10
+Contact:	Jack Wang <jinpu.wang@cloud.ionos.com> Danil Kipnis <danil.kipnis@cloud.ionos.com>
+Description:	Write "1" to the file to close the device on server side. Please
+		note that the client side device will not be closed, read or
+		write to the device will get -ENOTCONN.