From: Bartosz Golaszewski <redacted>

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 <redacted>
Acked-by: Vlastimil Babka <redacted>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Borislav Petkov <redacted>
Cc: Christian Knig <christian.koenig@amd.com>
Cc: Christoph Lameter <redacted>
Cc: Daniel Vetter <redacted>
Cc: Daniel Vetter <redacted>
Cc: David Airlie <redacted>
Cc: David Rientjes <rientjes@google.com>
Cc: Gustavo Padovan <redacted>
Cc: James Morse <james.morse@arm.com>
Cc: Jaroslav Kysela <perex@perex.cz>
Cc: Jason Wang <redacted>
Cc: Joonsoo Kim <redacted>
Cc: Linus Walleij <redacted>
Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Cc: Mauro Carvalho Chehab <mchehab@kernel.org>
Cc: Maxime Ripard <mripard@kernel.org>
Cc: "Michael S . Tsirkin" <mst@redhat.com>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: Robert Richter <rric@kernel.org>
Cc: Sumit Semwal <sumit.semwal@linaro.org>
Cc: Takashi Iwai <tiwai@suse.com>
Cc: Takashi Iwai <redacted>
Cc: Thomas Zimmermann <tzimmermann@suse.de>
Cc: Tony Luck <tony.luck@intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Lad Prabhakar <prabhakar.mahadev-lad.rj@bp.renesas.com>
---
 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