Re: net/sctp: slab-out-of-bounds in sctp_sf_ootb

[Marcelo Ricardo Leitner]

Hi Andrey,

On Mon, Oct 24, 2016 at 05:30:04PM +0200, Andrey Konovalov wrote:
> The problem is that sctp_walk_errors walks the chunk before its length
> is checked for overflow.

Exactly. The check is done too late, for the 2nd and subsequent chunks
only.
Please try the following patch, thanks. Note: not even compile tested.

---8<---

diff --git a/net/sctp/sm_statefuns.c b/net/sctp/sm_statefuns.c
index 026e3bca4a94..8ec20a64a3f8 100644
--- a/net/sctp/sm_statefuns.c
+++ b/net/sctp/sm_statefuns.c
@@ -3422,6 +3422,12 @@ sctp_disposition_t sctp_sf_ootb(struct net *net,
                        return sctp_sf_violation_chunklen(net, ep, asoc, type, 
arg,
                                                  commands);
 
+               /* Report violation if chunk len overflows */
+               ch_end = ((__u8 *)ch) + SCTP_PAD4(ntohs(ch->length));
+               if (ch_end > skb_tail_pointer(skb))
+                       return sctp_sf_violation_chunklen(net, ep, asoc, type, 
arg,
+                                                 commands);
+
                /* Now that we know we at least have a chunk header,
                 * do things that are type appropriate.
                 */
@@ -3453,12 +3459,6 @@ sctp_disposition_t sctp_sf_ootb(struct net *net,
                        }
                }
 
-               /* Report violation if chunk len overflows */
-               ch_end = ((__u8 *)ch) + SCTP_PAD4(ntohs(ch->length));
-               if (ch_end > skb_tail_pointer(skb))
-                       return sctp_sf_violation_chunklen(net, ep, asoc, type, 
arg,
-                                                 commands);
-
                ch = (sctp_chunkhdr_t *) ch_end;
        } while (ch_end < skb_tail_pointer(skb));