sctp: properly validate chunk size in sctp_sf_ootb()

A size validation fix similar to that in Commit 50619dbf8db7 ("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: [e-mail]
Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Signed-off-by: Xin Long <[e-mail]>
Link: https://patch.msgid.link/a2[e-mail]
Signed-off-by: Jakub Kicinski <[e-mail]>

net/sctp/sm_statefuns.c

···
 		}
 
 		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);