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

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Message-Id: <20210912131057.2285-1-len.baker@gmx.com>
Date:   Sun, 12 Sep 2021 15:10:57 +0200
From:   Len Baker <len.baker@....com>
To:     Simon Horman <simon.horman@...igine.com>,
        Jakub Kicinski <kuba@...nel.org>,
        "David S. Miller" <davem@...emloft.net>
Cc:     Len Baker <len.baker@....com>, Kees Cook <keescook@...omium.org>,
        "Gustavo A. R. Silva" <gustavoars@...nel.org>,
        oss-drivers@...igine.com, netdev@...r.kernel.org,
        linux-hardening@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH] nfp: 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 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/net/ethernet/netronome/nfp/nfp_net_repr.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/drivers/net/ethernet/netronome/nfp/nfp_net_repr.c b/drivers/net/ethernet/netronome/nfp/nfp_net_repr.c
index 3b8e675087de..369f6ae700c7 100644
--- a/drivers/net/ethernet/netronome/nfp/nfp_net_repr.c
+++ b/drivers/net/ethernet/netronome/nfp/nfp_net_repr.c
@@ -499,8 +499,7 @@ struct nfp_reprs *nfp_reprs_alloc(unsigned int num_reprs)
 {
 	struct nfp_reprs *reprs;

-	reprs = kzalloc(sizeof(*reprs) +
-			num_reprs * sizeof(struct net_device *), GFP_KERNEL);
+	reprs = kzalloc(struct_size(reprs, reprs, num_reprs), GFP_KERNEL);
 	if (!reprs)
 		return NULL;
 	reprs->num_reprs = num_reprs;
--
2.25.1