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>

1 files changed, 2 insertions, 1 deletions

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)"