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, 95 insertions, 0 deletions

diff --git a/lib/argv_split.c b/lib/argv_split.c
new file mode 100644
index 000000000..e28db8e3b
--- /dev/null
+++ b/lib/argv_split.c
@@ -0,0 +1,95 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Helper function for splitting a string into an argv-like array.
+ */
+
+#include <linux/kernel.h>
+#include <linux/ctype.h>
+#include <linux/string.h>
+#include <linux/slab.h>
+#include <linux/export.h>
+
+static int count_argc(const char *str)
+{
+	int count = 0;
+	bool was_space;
+
+	for (was_space = true; *str; str++) {
+		if (isspace(*str)) {
+			was_space = true;
+		} else if (was_space) {
+			was_space = false;
+			count++;
+		}
+	}
+
+	return count;
+}
+
+/**
+ * argv_free - free an argv
+ * @argv: the argument vector to be freed
+ *
+ * Frees an argv and the strings it points to.
+ */
+void argv_free(char **argv)
+{
+	argv--;
+	kfree(argv[0]);
+	kfree(argv);
+}
+EXPORT_SYMBOL(argv_free);
+
+/**
+ * argv_split - split a string at whitespace, returning an argv
+ * @gfp: the GFP mask used to allocate memory
+ * @str: the string to be split
+ * @argcp: returned argument count
+ *
+ * Returns: an array of pointers to strings which are split out from
+ * @str.  This is performed by strictly splitting on white-space; no
+ * quote processing is performed.  Multiple whitespace characters are
+ * considered to be a single argument separator.  The returned array
+ * is always NULL-terminated.  Returns NULL on memory allocation
+ * failure.
+ *
+ * The source string at `str' may be undergoing concurrent alteration via
+ * userspace sysctl activity (at least).  The argv_split() implementation
+ * attempts to handle this gracefully by taking a local copy to work on.
+ */
+char **argv_split(gfp_t gfp, const char *str, int *argcp)
+{
+	char *argv_str;
+	bool was_space;
+	char **argv, **argv_ret;
+	int argc;
+
+	argv_str = kstrndup(str, KMALLOC_MAX_SIZE - 1, gfp);
+	if (!argv_str)
+		return NULL;
+
+	argc = count_argc(argv_str);
+	argv = kmalloc_array(argc + 2, sizeof(*argv), gfp);
+	if (!argv) {
+		kfree(argv_str);
+		return NULL;
+	}
+
+	*argv = argv_str;
+	argv_ret = ++argv;
+	for (was_space = true; *argv_str; argv_str++) {
+		if (isspace(*argv_str)) {
+			was_space = true;
+			*argv_str = 0;
+		} else if (was_space) {
+			was_space = false;
+			*argv++ = argv_str;
+		}
+	}
+	*argv = NULL;
+
+	if (argcp)
+		*argcp = argc;
+	return argv_ret;
+}
+EXPORT_SYMBOL(argv_split);