[PATCH net] sctp: fix the issue that a __u16 variable may overflow in sctp_ulpq_renege

[Xin Long]

Now when reneging events in sctp_ulpq_renege(), the variable freed
could be increased by a __u16 value twice while freed is of __u16
type. It means freed may overflow at the second addition.

This patch is to fix it by using __u32 type for 'freed', while at
it, also to remove 'if (chunk)' check, as all renege commands are
generated in sctp_eat_data and it can't be NULL.

Reported-by: Marcelo Ricardo Leitner <marcelo.leit...@gmail.com>
Signed-off-by: Xin Long <lucien....@gmail.com>
---
 net/sctp/ulpqueue.c | 24 ++++++++----------------
 1 file changed, 8 insertions(+), 16 deletions(-)

diff --git a/net/sctp/ulpqueue.c b/net/sctp/ulpqueue.c
index a71be33..e36ec5d 100644
--- a/net/sctp/ulpqueue.c
+++ b/net/sctp/ulpqueue.c
@@ -1084,29 +1084,21 @@ void sctp_ulpq_partial_delivery(struct sctp_ulpq *ulpq,
 void sctp_ulpq_renege(struct sctp_ulpq *ulpq, struct sctp_chunk *chunk,
                      gfp_t gfp)
 {
-       struct sctp_association *asoc;
-       __u16 needed, freed;
-
-       asoc = ulpq->asoc;
+       struct sctp_association *asoc = ulpq->asoc;
+       __u32 freed = 0;
+       __u16 needed;
 
-       if (chunk) {
-               needed = ntohs(chunk->chunk_hdr->length);
-               needed -= sizeof(struct sctp_data_chunk);
-       } else
-               needed = SCTP_DEFAULT_MAXWINDOW;
-
-       freed = 0;
+       needed = ntohs(chunk->chunk_hdr->length) -
+                sizeof(struct sctp_data_chunk);
 
        if (skb_queue_empty(&asoc->base.sk->sk_receive_queue)) {
                freed = sctp_ulpq_renege_order(ulpq, needed);
-               if (freed < needed) {
+               if (freed < needed)
                        freed += sctp_ulpq_renege_frags(ulpq, needed - freed);
-               }
        }
        /* If able to free enough room, accept this chunk. */
-       if (chunk && (freed >= needed)) {
-               int retval;
-               retval = sctp_ulpq_tail_data(ulpq, chunk, gfp);
+       if (freed >= needed) {
+               int retval = sctp_ulpq_tail_data(ulpq, chunk, gfp);
                /*
                 * Enter partial delivery if chunk has not been
                 * delivered; otherwise, drain the reassembly queue.
-- 
2.1.0