Subject: Re: [PATCH net-next] sctp: fix slab-out-of-bounds in SCTP_DELAYED_SACK processing

From: Christoph Hellwig <[email-masked]>
Date: Thu, 23 Jul 2020 11:22:38 +0200

On Wed, Jul 22, 2020 at 05:42:31PM -0300, Marcelo Ricardo Leitner wrote:
> Cc'ing [email-masked].

What do you think of this version, which I think is a little cleaner?

diff --git a/net/sctp/socket.c b/net/sctp/socket.c
index 9a767f35971865..6ce460428af9f3 100644
--- a/net/sctp/socket.c
+++ b/net/sctp/socket.c
@@ -2749,31 +2749,12 @@ static void sctp_apply_asoc_delayed_ack(struct sctp_sack_info *params,
  *    timer to expire.  The default value for this is 2, setting this
  *    value to 1 will disable the delayed sack algorithm.
  */
-
-static int sctp_setsockopt_delayed_ack(struct sock *sk,
-				       struct sctp_sack_info *params,
-				       unsigned int optlen)
+static int __sctp_setsockopt_delayed_ack(struct sock *sk,
+					 struct sctp_sack_info *params)
 {
 	struct sctp_sock *sp = sctp_sk(sk);
 	struct sctp_association *asoc;
 
-	if (optlen == sizeof(struct sctp_sack_info)) {
-		if (params->sack_delay == 0 && params->sack_freq == 0)
-			return 0;
-	} else if (optlen == sizeof(struct sctp_assoc_value)) {
-		pr_warn_ratelimited(DEPRECATED
-				    "%s (pid %d) "
-				    "Use of struct sctp_assoc_value in delayed_ack socket option.\n"
-				    "Use struct sctp_sack_info instead\n",
-				    current->comm, task_pid_nr(current));
-
-		if (params->sack_delay == 0)
-			params->sack_freq = 1;
-		else
-			params->sack_freq = 0;
-	} else
-		return -EINVAL;
-
 	/* Validate value parameter. */
 	if (params->sack_delay > 500)
 		return -EINVAL;
@@ -2821,6 +2802,31 @@ static int sctp_setsockopt_delayed_ack(struct sock *sk,
 	return 0;
 }
 
+static int sctp_setsockopt_delayed_ack(struct sock *sk,
+				       struct sctp_sack_info *params,
+				       unsigned int optlen)
+{
+	if (optlen == sizeof(struct sctp_assoc_value)) {
+		struct sctp_sack_info p;
+
+		pr_warn_ratelimited(DEPRECATED
+				    "%s (pid %d) "
+				    "Use of struct sctp_assoc_value in delayed_ack socket option.\n"
+				    "Use struct sctp_sack_info instead\n",
+				    current->comm, task_pid_nr(current));
+
+		memcpy(&p, params, sizeof(struct sctp_assoc_value));
+		p.sack_freq = p.sack_delay ? 0 : 1;
+		return __sctp_setsockopt_delayed_ack(sk, &p);
+	}
+
+	if (optlen != sizeof(struct sctp_sack_info))
+		return -EINVAL;
+	if (params->sack_delay == 0 && params->sack_freq == 0)
+		return 0;
+	return __sctp_setsockopt_delayed_ack(sk, params);
+}
+
 /* 7.1.3 Initialization Parameters (SCTP_INITMSG)
  *
  * Applications can specify protocol parameters for the default association