ctcm: avoid wraparound in length of incoming data

Since the receive code should tolerate any incoming garbage, it
should be protected against a potential wraparound when manipulating
length values within incoming data.
block_len is unsigned, so a too large subtraction will cause a
wraparound.

Signed-off-by: Roel Kluin <roel.kluin@gmail.com>
Signed-off-by: Ursula Braun <ursula.braun@de.ibm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

2 files changed, 4 insertions, 4 deletions

diff --git a/drivers/s390/net/ctcm_fsms.c b/drivers/s390/net/ctcm_fsms.c
index f29c7086fc1..4ded9ac2c5e 100644
--- a/drivers/s390/net/ctcm_fsms.c
+++ b/drivers/s390/net/ctcm_fsms.c
@@ -410,9 +410,8 @@ static void chx_rx(fsm_instance *fi, int event, void *arg)
                 priv->stats.rx_length_errors++;
                                                 goto again;
         }
-        block_len -= 2;
-        if (block_len > 0) {
-                *((__u16 *)skb->data) = block_len;
+        if (block_len > 2) {
+                *((__u16 *)skb->data) = block_len - 2;
                 ctcm_unpack_skb(ch, skb);
         }
  again:
diff --git a/drivers/s390/net/ctcm_main.c b/drivers/s390/net/ctcm_main.c
index 59ce7fb7308..a7a25383db7 100644
--- a/drivers/s390/net/ctcm_main.c
+++ b/drivers/s390/net/ctcm_main.c
@@ -105,7 +105,8 @@ void ctcm_unpack_skb(struct channel *ch, struct sk_buff *pskb)
                         return;
                 }
                 pskb->protocol = ntohs(header->type);
-                if (header->length <= LL_HEADER_LENGTH) {
+                if ((header->length <= LL_HEADER_LENGTH) ||
+                    (len <= LL_HEADER_LENGTH)) {
                         if (!(ch->logflags & LOG_FLAG_ILLEGALSIZE)) {
                                 CTCM_DBF_TEXT_(ERROR, CTC_DBF_ERROR,
                                         "%s(%s): Illegal packet size %d(%d,%d)"