linux-kernel - Re: [PATCH v2] scsi: advansys: Prefer struct

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Date:   Mon, 27 Sep 2021 09:48:38 -0500
From:   "Gustavo A. R. Silva" <gustavoars@...nel.org>
To:     Len Baker <len.baker@....com>
Cc:     Matthew Wilcox <willy@...radead.org>,
        Hannes Reinecke <hare@...e.com>,
        "James E.J. Bottomley" <jejb@...ux.ibm.com>,
        "Martin K. Petersen" <martin.petersen@...cle.com>,
        Kees Cook <keescook@...omium.org>,
        linux-hardening@...r.kernel.org, linux-scsi@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] scsi: advansys: Prefer struct_size over open coded
 arithmetic

On Sat, Sep 25, 2021 at 01:42:05PM +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, use the struct_size() helper to do the arithmetic instead of the
> argument "size + count * size" in the kzalloc() function.
> 
> 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-coded-arithmetic-in-allocator-arguments
> 
> Signed-off-by: Len Baker <len.baker@....com>

Reviewed-by: Gustavo A. R. Silva <gustavoars@...nel.org>

> ---
> Changelog v1 -> v2
> - Rebase against v5.15-rc2

Don't use mainline for these sorts of patches . Use linux-next instead:

https://www.kernel.org/doc/man-pages/linux-next.html

Thanks
--
Gustavo

> - Remove the unnecessary "size" variable (Gustavo A. R. Silva).
> - Update the commit changelog to inform that this code was detected
>   using a Coccinelle script (Gustavo A. R. Silva).
> 
>  drivers/scsi/advansys.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/scsi/advansys.c b/drivers/scsi/advansys.c
> index ffb391967573..e341b3372482 100644
> --- a/drivers/scsi/advansys.c
> +++ b/drivers/scsi/advansys.c
> @@ -7477,8 +7477,8 @@ static int asc_build_req(struct asc_board *boardp, struct scsi_cmnd *scp,
>  			return ASC_ERROR;
>  		}
> 
> -		asc_sg_head = kzalloc(sizeof(asc_scsi_q->sg_head) +
> -			use_sg * sizeof(struct asc_sg_list), GFP_ATOMIC);
> +		asc_sg_head = kzalloc(struct_size(asc_sg_head, sg_list, use_sg),
> +				      GFP_ATOMIC);
>  		if (!asc_sg_head) {
>  			scsi_dma_unmap(scp);
>  			set_host_byte(scp, DID_SOFT_ERROR);
> --
> 2.25.1
>