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, 92 insertions, 0 deletions

diff --git a/fs/lockd/procfs.c b/fs/lockd/procfs.c
new file mode 100644
index 000000000..a01f08c8c
--- /dev/null
+++ b/fs/lockd/procfs.c
@@ -0,0 +1,92 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Procfs support for lockd
+ *
+ * Copyright (c) 2014 Jeff Layton <jlayton@primarydata.com>
+ */
+
+#include <linux/fs.h>
+#include <linux/proc_fs.h>
+#include <linux/module.h>
+#include <linux/nsproxy.h>
+#include <net/net_namespace.h>
+
+#include "netns.h"
+#include "procfs.h"
+
+/*
+ * We only allow strings that start with 'Y', 'y', or '1'.
+ */
+static ssize_t
+nlm_end_grace_write(struct file *file, const char __user *buf, size_t size,
+		    loff_t *pos)
+{
+	char *data;
+	struct lockd_net *ln = net_generic(current->nsproxy->net_ns,
+					   lockd_net_id);
+
+	if (size < 1)
+		return -EINVAL;
+
+	data = simple_transaction_get(file, buf, size);
+	if (IS_ERR(data))
+		return PTR_ERR(data);
+
+	switch(data[0]) {
+	case 'Y':
+	case 'y':
+	case '1':
+		locks_end_grace(&ln->lockd_manager);
+		break;
+	default:
+		return -EINVAL;
+	}
+
+	return size;
+}
+
+static ssize_t
+nlm_end_grace_read(struct file *file, char __user *buf, size_t size,
+		   loff_t *pos)
+{
+	struct lockd_net *ln = net_generic(current->nsproxy->net_ns,
+					   lockd_net_id);
+	char resp[3];
+
+	resp[0] = list_empty(&ln->lockd_manager.list) ? 'Y' : 'N';
+	resp[1] = '\n';
+	resp[2] = '\0';
+
+	return simple_read_from_buffer(buf, size, pos, resp, sizeof(resp));
+}
+
+static const struct proc_ops lockd_end_grace_proc_ops = {
+	.proc_write	= nlm_end_grace_write,
+	.proc_read	= nlm_end_grace_read,
+	.proc_lseek	= default_llseek,
+	.proc_release	= simple_transaction_release,
+};
+
+int __init
+lockd_create_procfs(void)
+{
+	struct proc_dir_entry *entry;
+
+	entry = proc_mkdir("fs/lockd", NULL);
+	if (!entry)
+		return -ENOMEM;
+	entry = proc_create("nlm_end_grace", S_IRUGO|S_IWUSR, entry,
+			    &lockd_end_grace_proc_ops);
+	if (!entry) {
+		remove_proc_entry("fs/lockd", NULL);
+		return -ENOMEM;
+	}
+	return 0;
+}
+
+void __exit
+lockd_remove_procfs(void)
+{
+	remove_proc_entry("fs/lockd/nlm_end_grace", NULL);
+	remove_proc_entry("fs/lockd", NULL);
+}