linux-kernel - Re: [PATCH v2] bnxt: avoid overflow in bnxt_get_nvram

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Date:   Sun, 19 Feb 2023 15:14:19 +0100
From:   Simon Horman <simon.horman@...igine.com>
To:     Maxim Korotkov <korotkov.maxim.s@...il.com>
Cc:     Michael Chan <michael.chan@...adcom.com>,
        Pavan Chebbi <pavan.chebbi@...adcom.com>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, lvc-project@...uxtesting.org
Subject: Re: [PATCH v2] bnxt: avoid overflow in bnxt_get_nvram_directory()

On Sun, Feb 19, 2023 at 11:46:56AM +0300, Maxim Korotkov wrote:
> The value of an arithmetic expression is subject
> of possible overflow due to a failure to cast operands to a larger data
> type before performing arithmetic. Used macro for multiplication instead
> operator for avoiding overflow.
> 
> Found by Security Code and Linux Verification
> Center (linuxtesting.org) with SVACE.
> 
> Fixes: c0c050c58d84 ("bnxt_en: New Broadcom ethernet driver.")
> Signed-off-by: Maxim Korotkov <korotkov.maxim.s@...il.com>
> Reviewed-by: Pavan Chebbi <pavan.chebbi@...adcom.com>

I agree that it is correct to use mul_u32_u32() for multiplication
of two u32 entities where the result is 64bit, avoiding overflow.

And I agree that the fixes tag indicates the commit where the code
in question was introduced.

However, it is not clear to me if this is a theoretical bug
or one that can manifest in practice - I think it implies that
buflen really can be > 4Gbytes.

And thus it is not clear to me if this patch should be for 'net' or
'net-next'.

> ---
> changelog:
> - added "fixes" tag.
>  drivers/net/ethernet/broadcom/bnxt/bnxt_ethtool.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/net/ethernet/broadcom/bnxt/bnxt_ethtool.c b/drivers/net/ethernet/broadcom/bnxt/bnxt_ethtool.c
> index ec573127b707..696f32dfe41f 100644
> --- a/drivers/net/ethernet/broadcom/bnxt/bnxt_ethtool.c
> +++ b/drivers/net/ethernet/broadcom/bnxt/bnxt_ethtool.c
> @@ -2862,7 +2862,7 @@ static int bnxt_get_nvram_directory(struct net_device *dev, u32 len, u8 *data)
>  	if (rc)
>  		return rc;
>  
> -	buflen = dir_entries * entry_length;
> +	buflen = mul_u32_u32(dir_entries, entry_length);
>  	buf = hwrm_req_dma_slice(bp, req, buflen, &dma_handle);
>  	if (!buf) {
>  		hwrm_req_drop(bp, req);
> -- 
> 2.37.2
>