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, 76 insertions, 0 deletions

diff --git a/fs/stack.c b/fs/stack.c
new file mode 100644
index 000000000..d8c782e06
--- /dev/null
+++ b/fs/stack.c
@@ -0,0 +1,76 @@
+// SPDX-License-Identifier: GPL-2.0-only
+#include <linux/export.h>
+#include <linux/fs.h>
+#include <linux/fs_stack.h>
+
+/* does _NOT_ require i_rwsem to be held.
+ *
+ * This function cannot be inlined since i_size_{read,write} is rather
+ * heavy-weight on 32-bit systems
+ */
+void fsstack_copy_inode_size(struct inode *dst, struct inode *src)
+{
+	loff_t i_size;
+	blkcnt_t i_blocks;
+
+	/*
+	 * i_size_read() includes its own seqlocking and protection from
+	 * preemption (see include/linux/fs.h): we need nothing extra for
+	 * that here, and prefer to avoid nesting locks than attempt to keep
+	 * i_size and i_blocks in sync together.
+	 */
+	i_size = i_size_read(src);
+
+	/*
+	 * But on 32-bit, we ought to make an effort to keep the two halves of
+	 * i_blocks in sync despite SMP or PREEMPTION - though stat's
+	 * generic_fillattr() doesn't bother, and we won't be applying quotas
+	 * (where i_blocks does become important) at the upper level.
+	 *
+	 * We don't actually know what locking is used at the lower level;
+	 * but if it's a filesystem that supports quotas, it will be using
+	 * i_lock as in inode_add_bytes().
+	 */
+	if (sizeof(i_blocks) > sizeof(long))
+		spin_lock(&src->i_lock);
+	i_blocks = src->i_blocks;
+	if (sizeof(i_blocks) > sizeof(long))
+		spin_unlock(&src->i_lock);
+
+	/*
+	 * If CONFIG_SMP or CONFIG_PREEMPTION on 32-bit, it's vital for
+	 * fsstack_copy_inode_size() to hold some lock around
+	 * i_size_write(), otherwise i_size_read() may spin forever (see
+	 * include/linux/fs.h).  We don't necessarily hold i_rwsem when this
+	 * is called, so take i_lock for that case.
+	 *
+	 * And if on 32-bit, continue our effort to keep the two halves of
+	 * i_blocks in sync despite SMP or PREEMPTION: use i_lock for that case
+	 * too, and do both at once by combining the tests.
+	 *
+	 * There is none of this locking overhead in the 64-bit case.
+	 */
+	if (sizeof(i_size) > sizeof(long) || sizeof(i_blocks) > sizeof(long))
+		spin_lock(&dst->i_lock);
+	i_size_write(dst, i_size);
+	dst->i_blocks = i_blocks;
+	if (sizeof(i_size) > sizeof(long) || sizeof(i_blocks) > sizeof(long))
+		spin_unlock(&dst->i_lock);
+}
+EXPORT_SYMBOL_GPL(fsstack_copy_inode_size);
+
+/* copy all attributes */
+void fsstack_copy_attr_all(struct inode *dest, const struct inode *src)
+{
+	dest->i_mode = src->i_mode;
+	dest->i_uid = src->i_uid;
+	dest->i_gid = src->i_gid;
+	dest->i_rdev = src->i_rdev;
+	inode_set_atime_to_ts(dest, inode_get_atime(src));
+	inode_set_mtime_to_ts(dest, inode_get_mtime(src));
+	inode_set_ctime_to_ts(dest, inode_get_ctime(src));
+	dest->i_blkbits = src->i_blkbits;
+	dest->i_flags = src->i_flags;
+	set_nlink(dest, src->i_nlink);
+}
+EXPORT_SYMBOL_GPL(fsstack_copy_attr_all);