tape: changer: handle libraries that sends wrong amount of data

if the library sends more data than advertised, simply cut it off,
but if it sends less data, bail out (depending on how much data is
missing, trying to parse it could lead to a panic, so bail out early)

Signed-off-by: Dominik Csapak <d.csapak@proxmox.com>

src/tape/changer/sg_pt_changer.rs

@@ -692,6 +692,15 @@ fn decode_element_status_page(
             bail!("got wrong first_element_address_reported"); // sanity check
         }
 
+        let len = head.byte_count_of_report_available;
+        let len = ((len[0] as usize) << 16) + ((len[1] as usize) << 8) + (len[2] as usize);
+
+        if len < reader.len() {
+            reader = &reader[..len];
+        } else if len > reader.len() {
+            bail!("wrong amount of data: expected {}, got {}", len, reader.len());
+        }
+
         loop {
             if reader.is_empty() {
                 break;