Subject: [PATCH v2 1/8] mm: slab: provide krealloc_array()

From: Bartosz Golaszewski <[email-masked]>
Date: Mon, 2 Nov 2020 16:20:30 +0100

From: Bartosz Golaszewski <[email-masked]>

When allocating an array of elements, users should check for
multiplication overflow or preferably use one of the provided helpers
like: kmalloc_array().

There's no krealloc_array() counterpart but there are many users who use
regular krealloc() to reallocate arrays. Let's provide an actual
krealloc_array() implementation.

While at it: add some documentation regarding krealloc.

Signed-off-by: Bartosz Golaszewski <[email-masked]>
Acked-by: Vlastimil Babka <[email-masked]>
---
 Documentation/core-api/memory-allocation.rst |  4 ++++
 include/linux/slab.h                         | 18 ++++++++++++++++++
 2 files changed, 22 insertions(+)

diff --git a/Documentation/core-api/memory-allocation.rst b/Documentation/core-api/memory-allocation.rst
index 4446a1ac36cc..6dc38b40439a 100644
--- a/Documentation/core-api/memory-allocation.rst
+++ b/Documentation/core-api/memory-allocation.rst
@@ -147,6 +147,10 @@ The address of a chunk allocated with `kmalloc` is aligned to at least
 ARCH_KMALLOC_MINALIGN bytes.  For sizes which are a power of two, the
 alignment is also guaranteed to be at least the respective size.
 
+Chunks allocated with `kmalloc` can be resized with `krealloc`. Similarly
+to `kmalloc_array`: a helper for resising arrays is provided in the form of
+`krealloc_array`.
+
 For large allocations you can use vmalloc() and vzalloc(), or directly
 request pages from the page allocator. The memory allocated by `vmalloc`
 and related functions is not physically contiguous.
diff --git a/include/linux/slab.h b/include/linux/slab.h
index dd6897f62010..be4ba5867ac5 100644
--- a/include/linux/slab.h
+++ b/include/linux/slab.h
@@ -592,6 +592,24 @@ static inline void *kmalloc_array(size_t n, size_t size, gfp_t flags)
 	return __kmalloc(bytes, flags);
 }
 
+/**
+ * krealloc_array - reallocate memory for an array.
+ * @p: pointer to the memory chunk to reallocate
+ * @new_n: new number of elements to alloc
+ * @new_size: new size of a single member of the array
+ * @flags: the type of memory to allocate (see kmalloc)
+ */
+static __must_check inline void *
+krealloc_array(void *p, size_t new_n, size_t new_size, gfp_t flags)
+{
+	size_t bytes;
+
+	if (unlikely(check_mul_overflow(new_n, new_size, &bytes)))
+		return NULL;
+
+	return krealloc(p, bytes, flags);
+}
+
 /**
  * kcalloc - allocate memory for an array. The memory is set to zero.
  * @n: number of elements.
-- 
2.29.1