sctp: properly validate chunk size in sctp_sf_ootb()

A size validation fix similar to that in Commit 50619db ("sctp: add
size validation when walking chunks") is also required in sctp_sf_ootb()
to address a crash reported by syzbot:

  BUG: KMSAN: uninit-value in sctp_sf_ootb+0x7f5/0xce0 net/sctp/sm_statefuns.c:3712
  sctp_sf_ootb+0x7f5/0xce0 net/sctp/sm_statefuns.c:3712
  sctp_do_sm+0x181/0x93d0 net/sctp/sm_sideeffect.c:1166
  sctp_endpoint_bh_rcv+0xc38/0xf90 net/sctp/endpointola.c:407
  sctp_inq_push+0x2ef/0x380 net/sctp/inqueue.c:88
  sctp_rcv+0x3831/0x3b20 net/sctp/input.c:243
  sctp4_rcv+0x42/0x50 net/sctp/protocol.c:1159
  ip_protocol_deliver_rcu+0xb51/0x13d0 net/ipv4/ip_input.c:205
  ip_local_deliver_finish+0x336/0x500 net/ipv4/ip_input.c:233

Reported-by: [email protected]
Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Signed-off-by: Xin Long <[email protected]>
Link: https://patch.msgid.link/a29ebb6d8b9f8affd0f9abb296faafafe10c17d8.1730223981.git.lucien.xin@gmail.com
Signed-off-by: Jakub Kicinski <[email protected]>

Author: lxin

net/sctp/sm_statefuns.c

@@ -3751,7 +3751,7 @@ enum sctp_disposition sctp_sf_ootb(struct net *net,
 		}
 
 		ch = (struct sctp_chunkhdr *)ch_end;
-	} while (ch_end < skb_tail_pointer(skb));
+	} while (ch_end + sizeof(*ch) < skb_tail_pointer(skb));
 
 	if (ootb_shut_ack)
 		return sctp_sf_shut_8_4_5(net, ep, asoc, type, arg, commands);