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From:   Len Baker <len.baker@gmx.com>
To:     Andrew Morton <akpm@linux-foundation.org>
Cc:     Len Baker <len.baker@gmx.com>, Kees Cook <keescook@chromium.org>,
        "Gustavo A. R. Silva" <gustavoars@kernel.org>,
        linux-hardening@vger.kernel.org, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org
Subject: [PATCH] mm/list_lru.c: prefer struct_size over open coded arithmetic
Date:   Sun, 17 Oct 2021 12:59:29 +0200
Message-Id: <20211017105929.9284-1-len.baker@gmx.com>
MIME-Version: 1.0
Content-Transfer-Encoding: quoted-printable
Precedence: bulk

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-co=
ded-arithmetic-in-allocator-arguments

Signed-off-by: Len Baker <len.baker@gmx.com>
=2D--
Hi,

this patch is built against the linux-next tree (tag next-20211015).

Regards,
Len

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

diff --git a/mm/list_lru.c b/mm/list_lru.c
index cd58790d0fb3..a6031f1c5bd7 100644
=2D-- a/mm/list_lru.c
+++ b/mm/list_lru.c
@@ -354,8 +354,7 @@ static int memcg_init_list_lru_node(struct list_lru_no=
de *nlru)
 	struct list_lru_memcg *memcg_lrus;
 	int size =3D memcg_nr_cache_ids;

-	memcg_lrus =3D kvmalloc(sizeof(*memcg_lrus) +
-			      size * sizeof(void *), GFP_KERNEL);
+	memcg_lrus =3D 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(struct list_lru_=
node *nlru,

 	old =3D rcu_dereference_protected(nlru->memcg_lrus,
 					lockdep_is_held(&list_lrus_mutex));
-	new =3D kvmalloc(sizeof(*new) + new_size * sizeof(void *), GFP_KERNEL);
+	new =3D kvmalloc(struct_size(new, lru, new_size), GFP_KERNEL);
 	if (!new)
 		return -ENOMEM;

@@ -398,7 +397,7 @@ static int memcg_update_list_lru_node(struct list_lru_=
node *nlru,
 		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
=2D-
2.25.1