Fix sctp privilege elevation (CVE-2006-3745)

sctp_make_abort_user() now takes the msg_len along with the msg
so that we don't have to recalculate the bytes in iovec.
It also uses memcpy_fromiovec() so that we don't go beyond the
length allocated.

It is good to have this fix even if verify_iovec() is fixed to
return error on overflow.
Signed-off-by: Sridhar Samudrala <sri@us.ibm.com>
Acked-by: David Miller <davem@davemloft.net>
Signed-off-by: Adrian Bunk <bunk@stusta.de>

include/net/sctp/sctp.h

@@ -405,19 +405,6 @@ static inline int sctp_list_single_entry(struct list_head *head)
 	return ((head->next != head) && (head->next == head->prev));
 }
 
-/* Calculate the size (in bytes) occupied by the data of an iovec.  */
-static inline size_t get_user_iov_size(struct iovec *iov, int iovlen)
-{
-	size_t retval = 0;
-
-	for (; iovlen > 0; --iovlen) {
-		retval += iov->iov_len;
-		iov++;
-	}
-
-	return retval;
-}
-
 /* Generate a random jitter in the range of -50% ~ +50% of input RTO. */
 static inline __s32 sctp_jitter(__u32 rto)
 {

include/net/sctp/sm.h

@@ -221,8 +221,7 @@ struct sctp_chunk *sctp_make_abort_no_data(const struct sctp_association *,
 				      const struct sctp_chunk *,
 				      __u32 tsn);
 struct sctp_chunk *sctp_make_abort_user(const struct sctp_association *,
-				   const struct sctp_chunk *,
-				   const struct msghdr *);
+					const struct msghdr *, size_t msg_len);
 struct sctp_chunk *sctp_make_abort_violation(const struct sctp_association *,
 				   const struct sctp_chunk *,
 				   const __u8 *,

net/sctp/sm_make_chunk.c

@@ -806,38 +806,26 @@ struct sctp_chunk *sctp_make_abort_no_data(
 
 /* Helper to create ABORT with a SCTP_ERROR_USER_ABORT error.  */
 struct sctp_chunk *sctp_make_abort_user(const struct sctp_association *asoc,
-				   const struct sctp_chunk *chunk,
-				   const struct msghdr *msg)
+					const struct msghdr *msg,
+					size_t paylen)
 {
 	struct sctp_chunk *retval;
-	void *payload = NULL, *payoff;
-	size_t paylen = 0;
-	struct iovec *iov = NULL;
-	int iovlen = 0;
-
-	if (msg) {
-		iov = msg->msg_iov;
-		iovlen = msg->msg_iovlen;
-		paylen = get_user_iov_size(iov, iovlen);
-	}
+	void *payload = NULL;
+	int err;
 
-	retval = sctp_make_abort(asoc, chunk, sizeof(sctp_errhdr_t) + paylen);
+	retval = sctp_make_abort(asoc, NULL, sizeof(sctp_errhdr_t) + paylen);
 	if (!retval)
 		goto err_chunk;
 
 	if (paylen) {
 		/* Put the msg_iov together into payload.  */
-		payload = kmalloc(paylen, GFP_ATOMIC);
+		payload = kmalloc(paylen, GFP_KERNEL);
 		if (!payload)
 			goto err_payload;
-		payoff = payload;
 
-		for (; iovlen > 0; --iovlen) {
-			if (copy_from_user(payoff, iov->iov_base,iov->iov_len))
-				goto err_copy;
-			payoff += iov->iov_len;
-			iov++;
-		}
+		err = memcpy_fromiovec(payload, msg->msg_iov, paylen);
+		if (err < 0)
+			goto err_copy;
 	}
 
 	sctp_init_cause(retval, SCTP_ERROR_USER_ABORT, payload, paylen);

net/sctp/sm_statefuns.c

@@ -4023,18 +4023,12 @@ sctp_disposition_t sctp_sf_do_9_1_prm_abort(
 	 * from its upper layer, but retransmits data to the far end
 	 * if necessary to fill gaps.
 	 */
-	struct msghdr *msg = arg;
-	struct sctp_chunk *abort;
+	struct sctp_chunk *abort = arg;
 	sctp_disposition_t retval;
 
 	retval = SCTP_DISPOSITION_CONSUME;
 
-	/* Generate ABORT chunk to send the peer.  */
-	abort = sctp_make_abort_user(asoc, NULL, msg);
-	if (!abort)
-		retval = SCTP_DISPOSITION_NOMEM;
-	else
-		sctp_add_cmd_sf(commands, SCTP_CMD_REPLY, SCTP_CHUNK(abort));
+	sctp_add_cmd_sf(commands, SCTP_CMD_REPLY, SCTP_CHUNK(abort));
 
 	/* Even if we can't send the ABORT due to low memory delete the
 	 * TCB.  This is a departure from our typical NOMEM handling.
@@ -4156,8 +4150,7 @@ sctp_disposition_t sctp_sf_cookie_wait_prm_abort(
 	void *arg,
 	sctp_cmd_seq_t *commands)
 {
-	struct msghdr *msg = arg;
-	struct sctp_chunk *abort;
+	struct sctp_chunk *abort = arg;
 	sctp_disposition_t retval;
 
 	/* Stop T1-init timer */
@@ -4165,12 +4158,7 @@ sctp_disposition_t sctp_sf_cookie_wait_prm_abort(
 			SCTP_TO(SCTP_EVENT_TIMEOUT_T1_INIT));
 	retval = SCTP_DISPOSITION_CONSUME;
 
-	/* Generate ABORT chunk to send the peer */
-	abort = sctp_make_abort_user(asoc, NULL, msg);
-	if (!abort)
-		retval = SCTP_DISPOSITION_NOMEM;
-	else
-		sctp_add_cmd_sf(commands, SCTP_CMD_REPLY, SCTP_CHUNK(abort));
+	sctp_add_cmd_sf(commands, SCTP_CMD_REPLY, SCTP_CHUNK(abort));
 
 	sctp_add_cmd_sf(commands, SCTP_CMD_NEW_STATE,
 			SCTP_STATE(SCTP_STATE_CLOSED));

net/sctp/socket.c

@@ -1476,8 +1476,16 @@ SCTP_STATIC int sctp_sendmsg(struct kiocb *iocb, struct sock *sk,
 			goto out_unlock;
 		}
 		if (sinfo_flags & SCTP_ABORT) {
+			struct sctp_chunk *chunk;
+
+			chunk = sctp_make_abort_user(asoc, msg, msg_len);
+			if (!chunk) {
+				err = -ENOMEM;
+				goto out_unlock;
+			}
+
 			SCTP_DEBUG_PRINTK("Aborting association: %p\n", asoc);
-			sctp_primitive_ABORT(asoc, msg);
+			sctp_primitive_ABORT(asoc, chunk);
 			err = 0;
 			goto out_unlock;
 		}