[PATCH] net/mlx5: DR, Prefer kcalloc 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, refactor the code a bit to use the purpose specific kcalloc()
function instead of the argument 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 <redacted>
---
 .../net/ethernet/mellanox/mlx5/core/steering/dr_action.c  | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/drivers/net/ethernet/mellanox/mlx5/core/steering/dr_action.c b/drivers/net/ethernet/mellanox/mlx5/core/steering/dr_action.c
index 6475ba35cf6b..e8957dad3bb1 100644
--- a/drivers/net/ethernet/mellanox/mlx5/core/steering/dr_action.c
+++ b/drivers/net/ethernet/mellanox/mlx5/core/steering/dr_action.c

@@ -716,6 +716,7 @@ mlx5dr_action_create_mult_dest_tbl(struct mlx5dr_domain *dmn,
 	struct mlx5dr_action *action;
 	bool reformat_req = false;
 	u32 num_of_ref = 0;
+	u32 ref_act_cnt;
 	int ret;
 	int i;

@@ -724,11 +725,14 @@ mlx5dr_action_create_mult_dest_tbl(struct mlx5dr_domain *dmn,
 		return NULL;
 	}

-	hw_dests = kzalloc(sizeof(*hw_dests) * num_of_dests, GFP_KERNEL);
+	hw_dests = kcalloc(num_of_dests, sizeof(*hw_dests), GFP_KERNEL);
 	if (!hw_dests)
 		return NULL;

-	ref_actions = kzalloc(sizeof(*ref_actions) * num_of_dests * 2, GFP_KERNEL);
+	if (unlikely(check_mul_overflow(num_of_dests, 2u, &ref_act_cnt)))
+		goto free_hw_dests;
+
+	ref_actions = kcalloc(ref_act_cnt, sizeof(*ref_actions), GFP_KERNEL);
 	if (!ref_actions)
 		goto free_hw_dests;

--

2.25.1

On Sun, 2021-09-05 at 09:49 +0200, Len Baker wrote:

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, refactor the code a bit to use the purpose specific kcalloc()
function instead of the argument 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 <redacted>

applied to net-next-mlx5,

Thanks.

On Sun, Sep 05, 2021 at 09:49:36AM +0200, Len Baker wrote:

In the future, consider array3_size(), but this is fine too. :)

-Kees

 	if (!ref_actions)
 		goto free_hw_dests;

--
2.25.1

-- 
Kees Cook

Hi,

On Mon, Sep 20, 2021 at 09:06:35PM -0700, Kees Cook wrote:

quoted

-	ref_actions = kzalloc(sizeof(*ref_actions) * num_of_dests * 2, GFP_KERNEL);
+	if (unlikely(check_mul_overflow(num_of_dests, 2u, &ref_act_cnt)))
+		goto free_hw_dests;
+
+	ref_actions = kcalloc(ref_act_cnt, sizeof(*ref_actions), GFP_KERNEL);

In the future, consider array3_size(), but this is fine too. :)

Ok, thanks for the advise.

Regards,
Len