[patch 058/262] mm/list_lru.c: prefer struct_size over open coded arithmetic

Andrew Morton
2021-11-05T20:37:43Z

From: Len Baker <len.baker@gmx.com>
Subject: mm/list_lru.c: prefer struct_size over open coded arithmetic

As noted in the "Deprecated Interfaces, Language Features, Attributes, and
Conventions" documentation [1], size calculations (especially
multiplication) should not be performed in memory allocator (or similar)
function arguments due to the risk of them overflowing. This could lead
to values wrapping around and a smaller allocation being made than the
caller was expecting. Using those allocations could lead to linear
overflows of heap memory and other misbehaviors.

So, use the struct_size() helper to do the arithmetic instead of the
argument "size + count * size" in the kvmalloc() functions.

Also, take the opportunity to refactor the memcpy() call to use the
flex_array_size() helper.

This code was detected with the help of Coccinelle and audited and fixed
manually.

[1] https://www.kernel.org/doc/html/latest/process/deprecated.html#open-coded-arithmetic-in-allocator-arguments

Link: https://lkml.kernel.org/r/20211017105929.9284-1-len.baker@gmx.com
Signed-off-by: Len Baker <len.baker@gmx.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: "Gustavo A. R. Silva" <gustavoars@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

mm/list_lru.c | 7 +++----
1 file changed, 3 insertions(+), 4 deletions(-)

--- a/mm/list_lru.c~mm-list_lruc-prefer-struct_size-over-open-coded-arithmetic
+++ a/mm/list_lru.c
@@ -354,8 +354,7 @@ static int memcg_init_list_lru_node(stru
struct list_lru_memcg *memcg_lrus;
int size = memcg_nr_cache_ids;

- memcg_lrus = kvmalloc(sizeof(*memcg_lrus) +
- size * sizeof(void *), GFP_KERNEL);
+ memcg_lrus = kvmalloc(struct_size(memcg_lrus, lru, size), GFP_KERNEL);
if (!memcg_lrus)
return -ENOMEM;

@@ -389,7 +388,7 @@ static int memcg_update_list_lru_node(st

old = rcu_dereference_protected(nlru->memcg_lrus,
lockdep_is_held(&list_lrus_mutex));
- new = kvmalloc(sizeof(*new) + new_size * sizeof(void *), GFP_KERNEL);
+ new = kvmalloc(struct_size(new, lru, new_size), GFP_KERNEL);
if (!new)
return -ENOMEM;

@@ -398,7 +397,7 @@ static int memcg_update_list_lru_node(st
return -ENOMEM;
}

- memcpy(&new->lru, &old->lru, old_size * sizeof(void *));
+ memcpy(&new->lru, &old->lru, flex_array_size(new, lru, old_size));

/*
* The locking below allows readers that hold nlru->lock avoid taking
_