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, 64 insertions, 0 deletions

diff --git a/lib/kasprintf.c b/lib/kasprintf.c
new file mode 100644
index 000000000..cd2f5974e
--- /dev/null
+++ b/lib/kasprintf.c
@@ -0,0 +1,64 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ *  linux/lib/kasprintf.c
+ *
+ *  Copyright (C) 1991, 1992  Linus Torvalds
+ */
+
+#include <linux/stdarg.h>
+#include <linux/export.h>
+#include <linux/slab.h>
+#include <linux/types.h>
+#include <linux/string.h>
+
+/* Simplified asprintf. */
+char *kvasprintf(gfp_t gfp, const char *fmt, va_list ap)
+{
+	unsigned int first, second;
+	char *p;
+	va_list aq;
+
+	va_copy(aq, ap);
+	first = vsnprintf(NULL, 0, fmt, aq);
+	va_end(aq);
+
+	p = kmalloc_track_caller(first+1, gfp);
+	if (!p)
+		return NULL;
+
+	second = vsnprintf(p, first+1, fmt, ap);
+	WARN(first != second, "different return values (%u and %u) from vsnprintf(\"%s\", ...)",
+	     first, second, fmt);
+
+	return p;
+}
+EXPORT_SYMBOL(kvasprintf);
+
+/*
+ * If fmt contains no % (or is exactly %s), use kstrdup_const. If fmt
+ * (or the sole vararg) points to rodata, we will then save a memory
+ * allocation and string copy. In any case, the return value should be
+ * freed using kfree_const().
+ */
+const char *kvasprintf_const(gfp_t gfp, const char *fmt, va_list ap)
+{
+	if (!strchr(fmt, '%'))
+		return kstrdup_const(fmt, gfp);
+	if (!strcmp(fmt, "%s"))
+		return kstrdup_const(va_arg(ap, const char*), gfp);
+	return kvasprintf(gfp, fmt, ap);
+}
+EXPORT_SYMBOL(kvasprintf_const);
+
+char *kasprintf(gfp_t gfp, const char *fmt, ...)
+{
+	va_list ap;
+	char *p;
+
+	va_start(ap, fmt);
+	p = kvasprintf(gfp, fmt, ap);
+	va_end(ap);
+
+	return p;
+}
+EXPORT_SYMBOL(kasprintf);