linux-kernel - Re: [PATCH 1/2][next] scsi: hptiop: Replace one-element array with flexible-array member

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Message-ID: <202209232240.747B2B5FCC@keescook>
Date:   Fri, 23 Sep 2022 23:01:46 -0700
From:   Kees Cook <keescook@...omium.org>
To:     "Gustavo A. R. Silva" <gustavoars@...nel.org>
Cc:     HighPoint Linux Team <linux@...hpoint-tech.com>,
        "James E.J. Bottomley" <jejb@...ux.ibm.com>,
        "Martin K. Petersen" <martin.petersen@...cle.com>,
        linux-scsi@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-hardening@...r.kernel.org
Subject: Re: [PATCH 1/2][next] scsi: hptiop: Replace one-element array with
 flexible-array member

On Thu, Sep 22, 2022 at 11:53:23AM -0500, Gustavo A. R. Silva wrote:
> One-element arrays are deprecated, and we are replacing them with flexible
> array members instead. So, replace one-element array with flexible-array
> member in struct hpt_iop_request_scsi_command and refactor the rest of the
> code, accordingly.
> 
> The following pieces of code suggest that the one element of array sg_list
> in struct hpt_iop_request_scsi_command is not taken into account when
> calculating the total size for both struct hpt_iop_request_scsi_command
> and the maximum number of elements sg_list will contain:
> 
> 1047         req->header.size = cpu_to_le32(
> 1048                                 sizeof(struct hpt_iop_request_scsi_command)
> 1049                                  - sizeof(struct hpt_iopsg)
> 1050                                  + sg_count * sizeof(struct hpt_iopsg));
> 
> 1400         req_size = sizeof(struct hpt_iop_request_scsi_command)                            1401                 + sizeof(struct hpt_iopsg) * (hba->max_sg_descriptors - 1);

Accidentally merge line above ("1401" should start a new line).

> So it's safe to replace the one-element array with a flexible-array
> member and update the code above, accordingly: now we don't need to
> subtract sizeof(struct hpt_iopsg) from sizeof(struct hpt_iop_request_scsi_command)
> because this is implicitly done by the flex-array transformation.

The only binary output change I see is from the line numbers changing
from the patch, as the argument to __might_sleep() is adjusted:

...
│       call   d1 <hptiop_reset+0x74>
│   R_X86_64_PLT32      __x86_indirect_thunk_rax-0x4
│ -     mov    $0x434,%esi
│ +     mov    $0x433,%esi
│       mov    $0x0,%rdi
│   R_X86_64_32S        .rodata.str1.1
│       call   e2 <hptiop_reset+0x85>
│   R_X86_64_PLT32      __might_sleep-0x4
...

So this looks good!

Reviewed-by: Kees Cook <keescook@...omium.org>

-- 
Kees Cook