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, 71 insertions, 0 deletions

diff --git a/Documentation/userspace-api/index.rst b/Documentation/userspace-api/index.rst
new file mode 100644
index 000000000..a68b1bea5
--- /dev/null
+++ b/Documentation/userspace-api/index.rst
@@ -0,0 +1,71 @@
+=====================================
+The Linux kernel user-space API guide
+=====================================
+
+.. _man-pages: https://www.kernel.org/doc/man-pages/
+
+While much of the kernel's user-space API is documented elsewhere
+(particularly in the man-pages_ project), some user-space information can
+also be found in the kernel tree itself.  This manual is intended to be the
+place where this information is gathered.
+
+
+System calls
+============
+
+.. toctree::
+   :maxdepth: 1
+
+   unshare
+   futex2
+   ebpf/index
+   ioctl/index
+   mseal
+   rseq
+
+Security-related interfaces
+===========================
+
+.. toctree::
+   :maxdepth: 1
+
+   no_new_privs
+   seccomp_filter
+   landlock
+   lsm
+   mfd_noexec
+   spec_ctrl
+   tee
+   check_exec
+
+Devices and I/O
+===============
+
+.. toctree::
+   :maxdepth: 1
+
+   accelerators/ocxl
+   dma-buf-heaps
+   dma-buf-alloc-exchange
+   fwctl/index
+   gpio/index
+   iommufd
+   media/index
+   dcdbas
+   vduse
+   isapnp
+
+Everything else
+===============
+
+.. toctree::
+   :maxdepth: 1
+
+   ELF
+   liveupdate
+   netlink/index
+   sysfs-platform_profile
+   vduse
+   futex2
+   perf_ring_buffer
+   ntsync