[PATCH 007/437] mm/util: add iterdup_nul() and iterdup() helpers

[Jens Axboe]

This is identical to the memdup variants, except it operates on a struct
iov_iter rather than a direct user pointer.

Signed-off-by: Jens Axboe <axboe@xxxxxxxxx>
---
 include/linux/string.h |  4 +++
 mm/util.c              | 57 ++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 61 insertions(+)

diff --git a/include/linux/string.h b/include/linux/string.h
index 9ba8b4597009..1983d2bf8840 100644
--- a/include/linux/string.h
+++ b/include/linux/string.h
@@ -18,6 +18,10 @@ extern void *memdup_user(const void __user *, size_t);
 extern void *vmemdup_user(const void __user *, size_t);
 extern void *memdup_user_nul(const void __user *, size_t);
 
+struct iov_iter;
+void *iterdup_nul(struct iov_iter *, size_t);
+void *iterdup(struct iov_iter *, size_t);
+
 /**
  * memdup_array_user - duplicate array from user space
  * @src: source address in user space
diff --git a/mm/util.c b/mm/util.c
index 669397235787..5d701cf693b0 100644
--- a/mm/util.c
+++ b/mm/util.c
@@ -224,6 +224,32 @@ void *memdup_user(const void __user *src, size_t len)
 }
 EXPORT_SYMBOL(memdup_user);
 
+/**
+ * iterdup - duplicate memory region
+ *
+ * @src: source iov_iter
+ * @len: number of bytes to copy
+ *
+ * Return: an ERR_PTR() on failure.  Result is physically
+ * contiguous, to be freed by kfree().
+ */
+void *iterdup(struct iov_iter *src, size_t len)
+{
+	void *p;
+
+	p = kmalloc_track_caller(len, GFP_USER | __GFP_NOWARN);
+	if (!p)
+		return ERR_PTR(-ENOMEM);
+
+	if (!copy_from_iter_full(p, len, src)) {
+		kfree(p);
+		return ERR_PTR(-EFAULT);
+	}
+
+	return p;
+}
+EXPORT_SYMBOL(iterdup);
+
 /**
  * vmemdup_user - duplicate memory region from user space
  *
@@ -312,6 +338,37 @@ void *memdup_user_nul(const void __user *src, size_t len)
 }
 EXPORT_SYMBOL(memdup_user_nul);
 
+/**
+ * iterdup_nul - duplicate memory region from iov_iter and NUL-terminate
+ *
+ * @src: source address to copy from
+ * @len: number of bytes to copy
+ *
+ * Return: an ERR_PTR() on failure.
+ */
+void *iterdup_nul(struct iov_iter *src, size_t len)
+{
+	char *p;
+
+	/*
+	 * Always use GFP_KERNEL, since copy_from_iter_full() can sleep and
+	 * cause pagefault, which makes it pointless to use GFP_NOFS
+	 * or GFP_ATOMIC.
+	 */
+	p = kmalloc_track_caller(len + 1, GFP_KERNEL);
+	if (!p)
+		return ERR_PTR(-ENOMEM);
+
+	if (!copy_from_iter_full(p, len, src)) {
+		kfree(p);
+		return ERR_PTR(-EFAULT);
+	}
+	p[len] = '\0';
+
+	return p;
+}
+EXPORT_SYMBOL(iterdup_nul);
+
 /* Check if the vma is being used as a stack by this task */
 int vma_is_stack_for_current(struct vm_area_struct *vma)
 {
-- 
2.43.0