linux-kernel - [PATCH v4 1/3] scsi: 3w-9xxx: Use flexible array members to avoid struct padding

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Message-Id: <20200903034450.5491-1-samuel@sholland.org>
Date:   Wed,  2 Sep 2020 22:44:48 -0500
From:   Samuel Holland <samuel@...lland.org>
To:     Adam Radford <aradford@...il.com>,
        "James E.J. Bottomley" <jejb@...ux.ibm.com>,
        "Martin K. Petersen" <martin.petersen@...cle.com>
Cc:     Arnd Bergmann <arnd@...db.de>, Joe Perches <joe@...ches.com>,
        linux-kernel@...r.kernel.org, linux-scsi@...r.kernel.org,
        Samuel Holland <samuel@...lland.org>
Subject: [PATCH v4 1/3] scsi: 3w-9xxx: Use flexible array members to avoid struct padding

In preparation for removing the "#pragma pack(1)" from the driver, fix
all instances where a trailing array member could be replaced by a
flexible array member. Since a flexible array member has zero size, it
introduces no padding, whether or not the struct is packed.

Signed-off-by: Samuel Holland <samuel@...lland.org>
---

Changes since v3:
  - Consistently put sizeof(TW_Ioctl_Buf_Apache) before buffer_length.

---
 drivers/scsi/3w-9xxx.c | 16 ++++++++++------
 drivers/scsi/3w-9xxx.h |  4 ++--
 2 files changed, 12 insertions(+), 8 deletions(-)

diff --git a/drivers/scsi/3w-9xxx.c b/drivers/scsi/3w-9xxx.c
index 3337b1e80412..aad9b3b73e15 100644
--- a/drivers/scsi/3w-9xxx.c
+++ b/drivers/scsi/3w-9xxx.c
@@ -676,7 +676,9 @@ static long twa_chrdev_ioctl(struct file *file, unsigned int cmd, unsigned long
 	data_buffer_length_adjusted = (driver_command.buffer_length + 511) & ~511;
 
 	/* Now allocate ioctl buf memory */
-	cpu_addr = dma_alloc_coherent(&tw_dev->tw_pci_dev->dev, data_buffer_length_adjusted+sizeof(TW_Ioctl_Buf_Apache) - 1, &dma_handle, GFP_KERNEL);
+	cpu_addr = dma_alloc_coherent(&tw_dev->tw_pci_dev->dev,
+				      sizeof(TW_Ioctl_Buf_Apache) + data_buffer_length_adjusted,
+				      &dma_handle, GFP_KERNEL);
 	if (!cpu_addr) {
 		retval = TW_IOCTL_ERROR_OS_ENOMEM;
 		goto out2;
@@ -685,7 +687,7 @@ static long twa_chrdev_ioctl(struct file *file, unsigned int cmd, unsigned long
 	tw_ioctl = (TW_Ioctl_Buf_Apache *)cpu_addr;
 
 	/* Now copy down the entire ioctl */
-	if (copy_from_user(tw_ioctl, argp, driver_command.buffer_length + sizeof(TW_Ioctl_Buf_Apache) - 1))
+	if (copy_from_user(tw_ioctl, argp, sizeof(TW_Ioctl_Buf_Apache) + driver_command.buffer_length))
 		goto out3;
 
 	/* See which ioctl we are doing */
@@ -867,11 +869,13 @@ static long twa_chrdev_ioctl(struct file *file, unsigned int cmd, unsigned long
 	}
 
 	/* Now copy the entire response to userspace */
-	if (copy_to_user(argp, tw_ioctl, sizeof(TW_Ioctl_Buf_Apache) + driver_command.buffer_length - 1) == 0)
+	if (copy_to_user(argp, tw_ioctl, sizeof(TW_Ioctl_Buf_Apache) + driver_command.buffer_length) == 0)
 		retval = 0;
 out3:
 	/* Now free ioctl buf memory */
-	dma_free_coherent(&tw_dev->tw_pci_dev->dev, data_buffer_length_adjusted+sizeof(TW_Ioctl_Buf_Apache) - 1, cpu_addr, dma_handle);
+	dma_free_coherent(&tw_dev->tw_pci_dev->dev,
+			  sizeof(TW_Ioctl_Buf_Apache) + data_buffer_length_adjusted,
+			  cpu_addr, dma_handle);
 out2:
 	mutex_unlock(&tw_dev->ioctl_lock);
 out:
@@ -1392,7 +1396,7 @@ static void twa_load_sgl(TW_Device_Extension *tw_dev, TW_Command_Full *full_comm
 		newcommand->request_id__lunl =
 			cpu_to_le16(TW_REQ_LUN_IN(TW_LUN_OUT(newcommand->request_id__lunl), request_id));
 		if (length) {
-			newcommand->sg_list[0].address = TW_CPU_TO_SGL(dma_handle + sizeof(TW_Ioctl_Buf_Apache) - 1);
+			newcommand->sg_list[0].address = TW_CPU_TO_SGL(dma_handle + sizeof(TW_Ioctl_Buf_Apache));
 			newcommand->sg_list[0].length = cpu_to_le32(length);
 		}
 		newcommand->sgl_entries__lunh =
@@ -1407,7 +1411,7 @@ static void twa_load_sgl(TW_Device_Extension *tw_dev, TW_Command_Full *full_comm
 				sgl = (TW_SG_Entry *)((u32 *)oldcommand+oldcommand->size - (sizeof(TW_SG_Entry)/4) + pae);
 			else
 				sgl = (TW_SG_Entry *)((u32 *)oldcommand+TW_SGL_OUT(oldcommand->opcode__sgloffset));
-			sgl->address = TW_CPU_TO_SGL(dma_handle + sizeof(TW_Ioctl_Buf_Apache) - 1);
+			sgl->address = TW_CPU_TO_SGL(dma_handle + sizeof(TW_Ioctl_Buf_Apache));
 			sgl->length = cpu_to_le32(length);
 
 			oldcommand->size += pae;
diff --git a/drivers/scsi/3w-9xxx.h b/drivers/scsi/3w-9xxx.h
index d88cd3499bd5..e65dafda2e3e 100644
--- a/drivers/scsi/3w-9xxx.h
+++ b/drivers/scsi/3w-9xxx.h
@@ -588,7 +588,7 @@ typedef struct TAG_TW_Ioctl_Apache {
 	TW_Ioctl_Driver_Command driver_command;
         char padding[488];
 	TW_Command_Full firmware_command;
-	char data_buffer[1];
+	char data_buffer[];
 } TW_Ioctl_Buf_Apache;
 
 /* Lock structure for ioctl get/release lock */
@@ -604,7 +604,7 @@ typedef struct {
 	unsigned short	parameter_id;
 	unsigned short	parameter_size_bytes;
 	unsigned short  actual_parameter_size_bytes;
-	unsigned char	data[1];
+	unsigned char	data[];
 } TW_Param_Apache, *PTW_Param_Apache;
 
 /* Response queue */
-- 
2.26.2