sctp: implement memory accounting on rx path

sk_forward_alloc's updating is also done on rx path, but to be consistent
we change to use sk_mem_charge() in sctp_skb_set_owner_r().

In sctp_eat_data(), it's not enough to check sctp_memory_pressure only,
which doesn't work for mem_cgroup_sockets_enabled, so we change to use
sk_under_memory_pressure().

When it's under memory pressure, sk_mem_reclaim() and sk_rmem_schedule()
should be called on both RENEGE or CHUNK DELIVERY path exit the memory
pressure status as soon as possible.

Note that sk_rmem_schedule() is using datalen to make things easy there.
Reported-by: Matteo Croce <mcroce@redhat.com>
Tested-by: Matteo Croce <mcroce@redhat.com>
Acked-by: Neil Horman <nhorman@tuxdriver.com>
Acked-by: Marcelo Ricardo Leitner <marcelo.leitner@gmail.com>
Signed-off-by: Xin Long <lucien.xin@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

CVE-2019-3874

(backported from commit 9dde27de linux-next)
[tyhicks: Backport to 4.4:
 - SCTP_PAD4() was WORD_ROUND() in 4.4. It was later renamed in commit
   e2f036a9 ("sctp: rename WORD_TRUNC/ROUND macros").]
Signed-off-by: Tyler Hicks <tyhicks@canonical.com>
Acked-by: Stefan Bader <stefan.bader@canonical.com>
Acked-by: Kleber Sacilotto de Souza <kleber.souza@canonical.com>
Signed-off-by: Kleber Sacilotto de Souza <kleber.souza@canonical.com>

include/net/sctp/sctp.h

@@ -396,7 +396,7 @@ static inline void sctp_skb_set_owner_r(struct sk_buff *skb, struct sock *sk)
 	/*
 	 * This mimics the behavior of skb_set_owner_r
 	 */
-	sk->sk_forward_alloc -= event->rmem_len;
+	sk_mem_charge(sk, event->rmem_len);
 }
 
 /* Tests if the list has one and only one entry. */

net/sctp/sm_statefuns.c

@@ -6216,13 +6216,15 @@ static int sctp_eat_data(const struct sctp_association *asoc,
 	 * in sctp_ulpevent_make_rcvmsg will drop the frame if we grow our
 	 * memory usage too much
 	 */
-	if (*sk->sk_prot_creator->memory_pressure) {
+	if (sk_under_memory_pressure(sk)) {
 		if (sctp_tsnmap_has_gap(map) &&
 		    (sctp_tsnmap_get_ctsn(map) + 1) == tsn) {
 			pr_debug("%s: under pressure, reneging for tsn:%u\n",
 				 __func__, tsn);
 			deliver = SCTP_CMD_RENEGE;
-		 }
+		} else {
+			sk_mem_reclaim(sk);
+		}
 	}
 
 	/*

net/sctp/ulpevent.c

@@ -637,8 +637,9 @@ struct sctp_ulpevent *sctp_ulpevent_make_rcvmsg(struct sctp_association *asoc,
 						gfp_t gfp)
 {
 	struct sctp_ulpevent *event = NULL;
-	struct sk_buff *skb;
-	size_t padding, len;
+	struct sk_buff *skb = chunk->skb;
+	struct sock *sk = asoc->base.sk;
+	size_t padding, datalen;
 	int rx_count;
 
 	/*
@@ -649,15 +650,12 @@ struct sctp_ulpevent *sctp_ulpevent_make_rcvmsg(struct sctp_association *asoc,
 	if (asoc->ep->rcvbuf_policy)
 		rx_count = atomic_read(&asoc->rmem_alloc);
 	else
-		rx_count = atomic_read(&asoc->base.sk->sk_rmem_alloc);
+		rx_count = atomic_read(&sk->sk_rmem_alloc);
 
-	if (rx_count >= asoc->base.sk->sk_rcvbuf) {
+	datalen = ntohs(chunk->chunk_hdr->length);
 
-		if ((asoc->base.sk->sk_userlocks & SOCK_RCVBUF_LOCK) ||
-		    (!sk_rmem_schedule(asoc->base.sk, chunk->skb,
-				       chunk->skb->truesize)))
-			goto fail;
-	}
+	if (rx_count >= sk->sk_rcvbuf || !sk_rmem_schedule(sk, skb, datalen))
+		goto fail;
 
 	/* Clone the original skb, sharing the data.  */
 	skb = skb_clone(chunk->skb, gfp);
@@ -684,8 +682,7 @@ struct sctp_ulpevent *sctp_ulpevent_make_rcvmsg(struct sctp_association *asoc,
 	 * The sender should never pad with more than 3 bytes.  The receiver
 	 * MUST ignore the padding bytes.
 	 */
-	len = ntohs(chunk->chunk_hdr->length);
-	padding = WORD_ROUND(len) - len;
+	padding = WORD_ROUND(datalen) - datalen;
 
 	/* Fixup cloned skb with just this chunks data.  */
 	skb_trim(skb, chunk->chunk_end - padding - skb->data);

net/sctp/ulpqueue.c

@@ -1093,7 +1093,8 @@ void sctp_ulpq_renege(struct sctp_ulpq *ulpq, struct sctp_chunk *chunk,
 			freed += sctp_ulpq_renege_frags(ulpq, needed - freed);
 	}
 	/* If able to free enough room, accept this chunk. */
-	if (freed >= needed) {
+	if (sk_rmem_schedule(asoc->base.sk, chunk->skb, needed) &&
+	    freed >= needed) {
 		int retval = sctp_ulpq_tail_data(ulpq, chunk, gfp);
 		/*
 		 * Enter partial delivery if chunk has not been