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, 63 insertions, 0 deletions

diff --git a/Documentation/admin-guide/device-mapper/linear.rst b/Documentation/admin-guide/device-mapper/linear.rst
new file mode 100644
index 000000000..9d17fc6e6
--- /dev/null
+++ b/Documentation/admin-guide/device-mapper/linear.rst
@@ -0,0 +1,63 @@
+=========
+dm-linear
+=========
+
+Device-Mapper's "linear" target maps a linear range of the Device-Mapper
+device onto a linear range of another device.  This is the basic building
+block of logical volume managers.
+
+Parameters: <dev path> <offset>
+    <dev path>:
+	Full pathname to the underlying block-device, or a
+        "major:minor" device-number.
+    <offset>:
+	Starting sector within the device.
+
+
+Example scripts
+===============
+
+::
+
+  #!/bin/sh
+  # Create an identity mapping for a device
+  echo "0 `blockdev --getsz $1` linear $1 0" | dmsetup create identity
+
+::
+
+  #!/bin/sh
+  # Join 2 devices together
+  size1=`blockdev --getsz $1`
+  size2=`blockdev --getsz $2`
+  echo "0 $size1 linear $1 0
+  $size1 $size2 linear $2 0" | dmsetup create joined
+
+::
+
+  #!/usr/bin/perl -w
+  # Split a device into 4M chunks and then join them together in reverse order.
+
+  my $name = "reverse";
+  my $extent_size = 4 * 1024 * 2;
+  my $dev = $ARGV[0];
+  my $table = "";
+  my $count = 0;
+
+  if (!defined($dev)) {
+          die("Please specify a device.\n");
+  }
+
+  my $dev_size = `blockdev --getsz $dev`;
+  my $extents = int($dev_size / $extent_size) -
+                (($dev_size % $extent_size) ? 1 : 0);
+
+  while ($extents > 0) {
+          my $this_start = $count * $extent_size;
+          $extents--;
+          $count++;
+          my $this_offset = $extents * $extent_size;
+
+          $table .= "$this_start $extent_size linear $dev $this_offset\n";
+  }
+
+  `echo \"$table\" | dmsetup create $name`;