[PATCH v5 iwl-next] i40e: Use correct buffer size in i40e_dbg_command_read

[Kunwu Chan]

The size of "i40e_dbg_command_buf" is 256, the size of "name"
depends on "IFNAMSIZ", plus a null character and format size,
the total size is more than 256.

Improve readability and maintainability by replacing a hardcoded string
allocation and formatting by the use of the kasprintf() helper.

Fixes: 02e9c290814c ("i40e: debugfs interface")
Suggested-by: Simon Horman <horms@xxxxxxxxxx>
Suggested-by: Alexander Lobakin <aleksander.lobakin@xxxxxxxxx>
Suggested-by: Tony Nguyen <anthony.l.nguyen@xxxxxxxxx>
Cc: Kunwu Chan <kunwu.chan@xxxxxxxxxxx>
Signed-off-by: Kunwu Chan <chentao@xxxxxxxxxx>
---
v2
   - Update the size calculation with IFNAMSIZ and sizeof(i40e_dbg_command_buf)
v3
   - Use kasprintf to improve readability and maintainability
v4
   - Fix memory leak in error path
v5
   - Change the order of labels
---
 .../net/ethernet/intel/i40e/i40e_debugfs.c    | 20 ++++++++++---------
 1 file changed, 11 insertions(+), 9 deletions(-)

diff --git a/drivers/net/ethernet/intel/i40e/i40e_debugfs.c b/drivers/net/ethernet/intel/i40e/i40e_debugfs.c
index 88240571721a..78a7200211b2 100644
--- a/drivers/net/ethernet/intel/i40e/i40e_debugfs.c
+++ b/drivers/net/ethernet/intel/i40e/i40e_debugfs.c
@@ -72,29 +72,31 @@ static ssize_t i40e_dbg_command_read(struct file *filp, char __user *buffer,
 {
 	struct i40e_pf *pf = filp->private_data;
 	int bytes_not_copied;
-	int buf_size = 256;
 	char *buf;
 	int len;
 
 	/* don't allow partial reads */
 	if (*ppos != 0)
 		return 0;
-	if (count < buf_size)
-		return -ENOSPC;
 
-	buf = kzalloc(buf_size, GFP_KERNEL);
+	buf = kasprintf(GFP_KERNEL, "%s: %s\n",
+			pf->vsi[pf->lan_vsi]->netdev->name,
+			i40e_dbg_command_buf);
 	if (!buf)
 		return -ENOSPC;
 
-	len = snprintf(buf, buf_size, "%s: %s\n",
-		       pf->vsi[pf->lan_vsi]->netdev->name,
-		       i40e_dbg_command_buf);
+	len = strlen(buf) + 1;
+	if (count < len)
+		bytes_not_copied = -ENOSPC;
+	else if (copy_to_user(buffer, buf, len))
+		bytes_not_copied = -EFAULT;
+	else
+		bytes_not_copied = 0;
 
-	bytes_not_copied = copy_to_user(buffer, buf, len);
 	kfree(buf);
 
 	if (bytes_not_copied)
-		return -EFAULT;
+		return bytes_not_copied;
 
 	*ppos = len;
 	return len;
-- 
2.39.2