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, 68 insertions, 0 deletions

diff --git a/tools/perf/util/fncache.c b/tools/perf/util/fncache.c
new file mode 100644
index 000000000..bf9559c55
--- /dev/null
+++ b/tools/perf/util/fncache.c
@@ -0,0 +1,68 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/* Manage a cache of file names' existence */
+#include <pthread.h>
+#include <stdlib.h>
+#include <string.h>
+#include <unistd.h>
+#include <linux/compiler.h>
+#include "fncache.h"
+#include "hashmap.h"
+
+static struct hashmap *fncache;
+
+static size_t fncache__hash(long key, void *ctx __maybe_unused)
+{
+	return str_hash((const char *)key);
+}
+
+static bool fncache__equal(long key1, long key2, void *ctx __maybe_unused)
+{
+	return strcmp((const char *)key1, (const char *)key2) == 0;
+}
+
+static void fncache__init(void)
+{
+	fncache = hashmap__new(fncache__hash, fncache__equal, /*ctx=*/NULL);
+}
+
+static struct hashmap *fncache__get(void)
+{
+	static pthread_once_t fncache_once = PTHREAD_ONCE_INIT;
+
+	pthread_once(&fncache_once, fncache__init);
+
+	return fncache;
+}
+
+static bool lookup_fncache(const char *name, bool *res)
+{
+	long val;
+
+	if (!hashmap__find(fncache__get(), name, &val))
+		return false;
+
+	*res = (val != 0);
+	return true;
+}
+
+static void update_fncache(const char *name, bool res)
+{
+	char *old_key = NULL, *key = strdup(name);
+
+	if (key) {
+		hashmap__set(fncache__get(), key, res, &old_key, /*old_value*/NULL);
+		free(old_key);
+	}
+}
+
+/* No LRU, only use when bounded in some other way. */
+bool file_available(const char *name)
+{
+	bool res;
+
+	if (lookup_fncache(name, &res))
+		return res;
+	res = access(name, R_OK) == 0;
+	update_fncache(name, res);
+	return res;
+}