sctp: fix the issue that a __u16 variable may overflow in sctp_ulpq_renege

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.leitner@gmail.com>
Signed-off-by: Xin Long <lucien.xin@gmail.com>
Acked-by: Neil Horman <nhorman@tuxdriver.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 8 insertions, 16 deletions

diff --git a/net/sctp/ulpqueue.c b/net/sctp/ulpqueue.c
index a71be33f3afe..e36ec5dd64c6 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.