From: Bartosz Golaszewski <bgolaszewski@...>

commit f0dbd2bd1c22c6670e83ddcd46a9beb8b575e86d upstream.

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.

Link: https://lkml.kernel.org/r/20201109110654.12547-3-brgl@bgdev.pl
Signed-off-by: Bartosz Golaszewski <bgolaszewski@...>
Acked-by: Vlastimil Babka <vbabka@...>
Cc: Alexander Shishkin <alexander.shishkin@...>
Cc: Andy Shevchenko <andriy.shevchenko@...>
Cc: Borislav Petkov <bp@...>
Cc: Borislav Petkov <bp@...>
Cc: Christian Knig <christian.koenig@...>
Cc: Christoph Lameter <cl@...>
Cc: Daniel Vetter <daniel@...>
Cc: Daniel Vetter <daniel.vetter@...>
Cc: David Airlie <airlied@...>
Cc: David Rientjes <rientjes@...>
Cc: Gustavo Padovan <gustavo@...>
Cc: James Morse <james.morse@...>
Cc: Jaroslav Kysela <perex@...>
Cc: Jason Wang <jasowang@...>
Cc: Joonsoo Kim <iamjoonsoo.kim@...>
Cc: Linus Walleij <linus.walleij@...>
Cc: Maarten Lankhorst <maarten.lankhorst@...>
Cc: Mauro Carvalho Chehab <mchehab@...>
Cc: Maxime Ripard <mripard@...>
Cc: "Michael S . Tsirkin" <mst@...>
Cc: Pekka Enberg <penberg@...>
Cc: Robert Richter <rric@...>
Cc: Sumit Semwal <sumit.semwal@...>
Cc: Takashi Iwai <tiwai@...>
Cc: Takashi Iwai <tiwai@...>
Cc: Thomas Zimmermann <tzimmermann@...>
Cc: Tony Luck <tony.luck@...>
Signed-off-by: Andrew Morton <akpm@...>
Signed-off-by: Linus Torvalds <torvalds@...>
Signed-off-by: Lad Prabhakar <prabhakar.mahadev-lad.rj@...>
---
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..5954ddf6ee13 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 resizing 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.
--
2.17.1