i40e: clamp debugfs nvm read command

This issue was identified by the coverity checker where we were
not checking the upper limit on reads, reported by Hannes
Frederic Sowa.

Implement more specific limits on reads (min 1k, max 4k)

Signed-off-by: Jesse Brandeburg <jesse.brandeburg@intel.com>
CC: Hannes Frederic Sowa <hannes@stressinduktion.org>
Tested-by: Kavindya Deegala <kavindya.s.deegala@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>

drivers/net/ethernet/intel/i40e/i40e_debugfs.c

@@ -1742,11 +1742,13 @@ static ssize_t i40e_dbg_command_write(struct file *filp,
 			goto command_write_done;
 		}
 
-		/* Read at least 512 words */
-		if (buffer_len == 0)
-			buffer_len = 512;
+		/* set the max length */
+		buffer_len = min_t(u16, buffer_len, I40E_MAX_AQ_BUF_SIZE/2);
 
 		bytes = 2 * buffer_len;
+
+		/* read at least 1k bytes, no more than 4kB */
+		bytes = clamp(bytes, (u16)1024, (u16)I40E_MAX_AQ_BUF_SIZE);
 		buff = kzalloc(bytes, GFP_KERNEL);
 		if (!buff)
 			goto command_write_done;