linux-hardening - [PATCH] tifm: Prefer struct_size over open coded arithmetic

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Date:   Sun,  5 Sep 2021 17:37:07 +0200
From:   Len Baker <len.baker@....com>
To:     Alex Dubov <oakad@...oo.com>, Arnd Bergmann <arnd@...db.de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     Len Baker <len.baker@....com>, Kees Cook <keescook@...omium.org>,
        linux-hardening@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH] tifm: 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 + size * count" in the kzalloc() function.

[1] https://www.kernel.org/doc/html/v5.14/process/deprecated.html#open-coded-arithmetic-in-allocator-arguments

Signed-off-by: Len Baker <len.baker@....com>
---
 drivers/misc/tifm_core.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/drivers/misc/tifm_core.c b/drivers/misc/tifm_core.c
index 667e574a7df2..9babf171a035 100644
--- a/drivers/misc/tifm_core.c
+++ b/drivers/misc/tifm_core.c
@@ -177,8 +177,7 @@ struct tifm_adapter *tifm_alloc_adapter(unsigned int num_sockets,
 {
 	struct tifm_adapter *fm;

-	fm = kzalloc(sizeof(struct tifm_adapter)
-		     + sizeof(struct tifm_dev*) * num_sockets, GFP_KERNEL);
+	fm = kzalloc(struct_size(fm, sockets, num_sockets), GFP_KERNEL);
 	if (fm) {
 		fm->dev.class = &tifm_adapter_class;
 		fm->dev.parent = dev;
--
2.25.1