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);

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.

Link: https://github.com/KSPP/linux/issues/79
Link: https://github.com/KSPP/linux/issues/205
Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>
---
 drivers/scsi/hptiop.c | 3 +--
 drivers/scsi/hptiop.h | 2 +-
 2 files changed, 2 insertions(+), 3 deletions(-)

diff --git a/drivers/scsi/hptiop.c b/drivers/scsi/hptiop.c
index f18b770626e6..cfc6546e35a6 100644
--- a/drivers/scsi/hptiop.c
+++ b/drivers/scsi/hptiop.c
@@ -1046,7 +1046,6 @@ static int hptiop_queuecommand_lck(struct scsi_cmnd *scp)
 	req->lun = scp->device->lun;
 	req->header.size = cpu_to_le32(
 				sizeof(struct hpt_iop_request_scsi_command)
-				 - sizeof(struct hpt_iopsg)
 				 + sg_count * sizeof(struct hpt_iopsg));
 
 	memcpy(req->cdb, scp->cmnd, sizeof(req->cdb));
@@ -1398,7 +1397,7 @@ static int hptiop_probe(struct pci_dev *pcidev, const struct pci_device_id *id)
 	host->max_cmd_len = 16;
 
 	req_size = sizeof(struct hpt_iop_request_scsi_command)
-		+ sizeof(struct hpt_iopsg) * (hba->max_sg_descriptors - 1);
+		+ sizeof(struct hpt_iopsg) * hba->max_sg_descriptors;
 	if ((req_size & 0x1f) != 0)
 		req_size = (req_size + 0x1f) & ~0x1f;
 
diff --git a/drivers/scsi/hptiop.h b/drivers/scsi/hptiop.h
index 363d5a16243f..ef2f2aca598c 100644
--- a/drivers/scsi/hptiop.h
+++ b/drivers/scsi/hptiop.h
@@ -228,7 +228,7 @@ struct hpt_iop_request_scsi_command {
 	u8     pad1;
 	u8     cdb[16];
 	__le32 dataxfer_length;
-	struct hpt_iopsg sg_list[1];
+	struct hpt_iopsg sg_list[];
 };
 
 struct hpt_iop_request_ioctl_command {
-- 
2.34.1

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@chromium.org>

-- 
Kees Cook