[PATCH v2 1/2] libfs: Introduce tokenize_user_input()

[Cezary Rojewski]

Add new helper function to allow for splitting specified user string
into a sequence of integers. Internally it makes use of get_options() so
the returned sequence contains the integers extracted plus an additional
element that begins the sequence and specifies the integers count.

Suggested-by: Andy Shevchenko <andy.shevchenko@xxxxxxxxx>
Signed-off-by: Cezary Rojewski <cezary.rojewski@xxxxxxxxx>
---
 fs/libfs.c         | 45 +++++++++++++++++++++++++++++++++++++++++++++
 include/linux/fs.h |  1 +
 2 files changed, 46 insertions(+)

diff --git a/fs/libfs.c b/fs/libfs.c
index 31b0ddf01c31..078b23e26741 100644
--- a/fs/libfs.c
+++ b/fs/libfs.c
@@ -809,6 +809,51 @@ ssize_t simple_write_to_buffer(void *to, size_t available, loff_t *ppos,
 }
 EXPORT_SYMBOL(simple_write_to_buffer);
 
+/**
+ * tokenize_user_input - Split string into a sequence of integers
+ * @from:	The user space buffer to read from
+ * @ppos:	The current position in the buffer
+ * @count:	The maximum number of bytes to read
+ * @tkns:	Returned pointer to sequence of integers
+ *
+ * On success @tkns is allocated and initialized with a sequence of
+ * integers extracted from the @from plus an additional element that
+ * begins the sequence and specifies the integers count.
+ *
+ * Caller takes responsibility for freeing @tkns when it is no longer
+ * needed.
+ */
+int tokenize_user_input(const char __user *from, size_t count, int **tkns)
+{
+	int *ints, nints;
+	char *buf;
+	int ret = 0;
+
+	buf = memdup_user_nul(from, count);
+	if (IS_ERR(buf))
+		return PTR_ERR(buf);
+
+	get_options(buf, 0, &nints);
+	if (!nints) {
+		ret = -ENOENT;
+		goto free_buf;
+	}
+
+	ints = kcalloc(nints + 1, sizeof(*ints), GFP_KERNEL);
+	if (!ints) {
+		ret = -ENOMEM;
+		goto free_buf;
+	}
+
+	get_options(buf, nints + 1, ints);
+	*tkns = ints;
+
+free_buf:
+	kfree(buf);
+	return ret;
+}
+EXPORT_SYMBOL(tokenize_user_input);
+
 /**
  * memory_read_from_buffer - copy data from the buffer
  * @to: the kernel space buffer to read to
diff --git a/include/linux/fs.h b/include/linux/fs.h
index 9eced4cc286e..ab04cc7f9efa 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -3345,6 +3345,7 @@ extern ssize_t simple_read_from_buffer(void __user *to, size_t count,
 			loff_t *ppos, const void *from, size_t available);
 extern ssize_t simple_write_to_buffer(void *to, size_t available, loff_t *ppos,
 		const void __user *from, size_t count);
+extern int tokenize_user_input(const char __user *from, size_t count, int **tkns);
 
 extern int __generic_file_fsync(struct file *, loff_t, loff_t, int);
 extern int generic_file_fsync(struct file *, loff_t, loff_t, int);
-- 
2.25.1