+ mm-list_lruc-prefer-struct_size-over-open-coded-arithmetic.patch added to -mm tree

[akpm@xxxxxxxxxxxxxxxxxxxx]

The patch titled
     Subject: mm/list_lru.c: prefer struct_size over open coded arithmetic
has been added to the -mm tree.  Its filename is
     mm-list_lruc-prefer-struct_size-over-open-coded-arithmetic.patch

This patch should soon appear at
    https://ozlabs.org/~akpm/mmots/broken-out/mm-list_lruc-prefer-struct_size-over-open-coded-arithmetic.patch
and later at
    https://ozlabs.org/~akpm/mmotm/broken-out/mm-list_lruc-prefer-struct_size-over-open-coded-arithmetic.patch

Before you just go and hit "reply", please:
   a) Consider who else should be cc'ed
   b) Prefer to cc a suitable mailing list as well
   c) Ideally: find the original patch on the mailing list and do a
      reply-to-all to that, adding suitable additional cc's

*** Remember to use Documentation/process/submit-checklist.rst when testing your code ***

The -mm tree is included into linux-next and is updated
there every 3-4 working days

------------------------------------------------------
From: Len Baker <len.baker@xxxxxxx>
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-co=
ded-arithmetic-in-allocator-arguments

Link: https://lkml.kernel.org/r/20211017105929.9284-1-len.baker@xxxxxxx
Signed-off-by: Len Baker <len.baker@xxxxxxx>
Cc: Kees Cook <keescook@xxxxxxxxxxxx>
Cc: "Gustavo A. R. Silva" <gustavoars@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---

 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
_

Patches currently in -mm which might be from len.baker@xxxxxxx are

mm-list_lruc-prefer-struct_size-over-open-coded-arithmetic.patch