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, 96 insertions, 0 deletions

diff --git a/net/rxrpc/txbuf.c b/net/rxrpc/txbuf.c
new file mode 100644
index 000000000..55ef7a048
--- /dev/null
+++ b/net/rxrpc/txbuf.c
@@ -0,0 +1,96 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/* RxRPC Tx data buffering.
+ *
+ * Copyright (C) 2022 Red Hat, Inc. All Rights Reserved.
+ * Written by David Howells (dhowells@redhat.com)
+ */
+
+#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
+
+#include <linux/slab.h>
+#include "ar-internal.h"
+
+static atomic_t rxrpc_txbuf_debug_ids;
+atomic_t rxrpc_nr_txbuf;
+
+/*
+ * Allocate and partially initialise a data transmission buffer.
+ */
+struct rxrpc_txbuf *rxrpc_alloc_data_txbuf(struct rxrpc_call *call, size_t data_size,
+					   size_t data_align, gfp_t gfp)
+{
+	struct rxrpc_txbuf *txb;
+	size_t total, doff, jsize = sizeof(struct rxrpc_jumbo_header);
+	void *buf;
+
+	txb = kzalloc_obj(*txb, gfp);
+	if (!txb)
+		return NULL;
+
+	/* We put a jumbo header in the buffer, but not a full wire header to
+	 * avoid delayed-corruption problems with zerocopy.
+	 */
+	doff = round_up(jsize, data_align);
+	total = doff + data_size;
+
+	data_align = umax(data_align, L1_CACHE_BYTES);
+	mutex_lock(&call->conn->tx_data_alloc_lock);
+	buf = page_frag_alloc_align(&call->conn->tx_data_alloc, total, gfp,
+				    data_align);
+	mutex_unlock(&call->conn->tx_data_alloc_lock);
+	if (!buf) {
+		kfree(txb);
+		return NULL;
+	}
+
+	refcount_set(&txb->ref, 1);
+	txb->call_debug_id	= call->debug_id;
+	txb->debug_id		= atomic_inc_return(&rxrpc_txbuf_debug_ids);
+	txb->alloc_size		= data_size;
+	txb->space		= data_size;
+	txb->offset		= 0;
+	txb->flags		= call->conn->out_clientflag;
+	txb->seq		= call->send_top + 1;
+	txb->data		= buf + doff;
+
+	trace_rxrpc_txbuf(txb->debug_id, txb->call_debug_id, txb->seq, 1,
+			  rxrpc_txbuf_alloc_data);
+
+	atomic_inc(&rxrpc_nr_txbuf);
+	return txb;
+}
+
+void rxrpc_see_txbuf(struct rxrpc_txbuf *txb, enum rxrpc_txbuf_trace what)
+{
+	int r = refcount_read(&txb->ref);
+
+	trace_rxrpc_txbuf(txb->debug_id, txb->call_debug_id, txb->seq, r, what);
+}
+
+static void rxrpc_free_txbuf(struct rxrpc_txbuf *txb)
+{
+	trace_rxrpc_txbuf(txb->debug_id, txb->call_debug_id, txb->seq, 0,
+			  rxrpc_txbuf_free);
+	if (txb->data)
+		page_frag_free(txb->data);
+	kfree(txb);
+	atomic_dec(&rxrpc_nr_txbuf);
+}
+
+void rxrpc_put_txbuf(struct rxrpc_txbuf *txb, enum rxrpc_txbuf_trace what)
+{
+	unsigned int debug_id, call_debug_id;
+	rxrpc_seq_t seq;
+	bool dead;
+	int r;
+
+	if (txb) {
+		debug_id = txb->debug_id;
+		call_debug_id = txb->call_debug_id;
+		seq = txb->seq;
+		dead = __refcount_dec_and_test(&txb->ref, &r);
+		trace_rxrpc_txbuf(debug_id, call_debug_id, seq, r - 1, what);
+		if (dead)
+			rxrpc_free_txbuf(txb);
+	}
+}