9p: validate PDU length

This commit adds length check for the PDU size.
The size contained in the header has to match the actual size,
except for TCP (trans_fd.c) where actual length is not known ahead
and the header's length will be checked only against the validity
range.

Link: http://lkml.kernel.org/r/20180723154404.2406-1-tomasbortoli@gmail.com
Signed-off-by: Tomas Bortoli <tomasbortoli@gmail.com>
Reported-by: syzbot+65c6b72f284a39d416b4@syzkaller.appspotmail.com
To: Eric Van Hensbergen <ericvh@gmail.com>
To: Ron Minnich <rminnich@sandia.gov>
To: Latchesar Ionkov <lucho@ionkov.net>
Cc: David S. Miller <davem@davemloft.net>
Signed-off-by: Dominique Martinet <dominique.martinet@cea.fr>

net/9p/client.c

@@ -469,20 +469,11 @@ p9_parse_header(struct p9_fcall *pdu, int32_t *size, int8_t *type, int16_t *tag,
 	int err;
 
 	pdu->offset = 0;
-	if (pdu->size == 0)
-		pdu->size = 7;
 
 	err = p9pdu_readf(pdu, 0, "dbw", &r_size, &r_type, &r_tag);
 	if (err)
 		goto rewind_and_exit;
 
-	pdu->size = r_size;
-	pdu->id = r_type;
-	pdu->tag = r_tag;
-
-	p9_debug(P9_DEBUG_9P, "<<< size=%d type: %d tag: %d\n",
-		 pdu->size, pdu->id, pdu->tag);
-
 	if (type)
 		*type = r_type;
 	if (tag)
@@ -490,6 +481,16 @@ p9_parse_header(struct p9_fcall *pdu, int32_t *size, int8_t *type, int16_t *tag,
 	if (size)
 		*size = r_size;
 
+	if (pdu->size != r_size || r_size < 7) {
+		err = -EINVAL;
+		goto rewind_and_exit;
+	}
+
+	pdu->id = r_type;
+	pdu->tag = r_tag;
+
+	p9_debug(P9_DEBUG_9P, "<<< size=%d type: %d tag: %d\n",
+		 pdu->size, pdu->id, pdu->tag);
 
 rewind_and_exit:
 	if (rewind)
@@ -516,6 +517,12 @@ static int p9_check_errors(struct p9_client *c, struct p9_req_t *req)
 	int ecode;
 
 	err = p9_parse_header(req->rc, NULL, &type, NULL, 0);
+	if (req->rc->size >= c->msize) {
+		p9_debug(P9_DEBUG_ERROR,
+			 "requested packet size too big: %d\n",
+			 req->rc->size);
+		return -EIO;
+	}
 	/*
 	 * dump the response from server
 	 * This should be after check errors which poplulate pdu_fcall.

net/9p/trans_fd.c

@@ -325,7 +325,9 @@ static void p9_read_work(struct work_struct *work)
 	if ((!m->req) && (m->rc.offset == m->rc.capacity)) {
 		p9_debug(P9_DEBUG_TRANS, "got new header\n");
 
-		err = p9_parse_header(&m->rc, NULL, NULL, NULL, 0);
+		/* Header size */
+		m->rc.size = 7;
+		err = p9_parse_header(&m->rc, &m->rc.size, NULL, NULL, 0);
 		if (err) {
 			p9_debug(P9_DEBUG_ERROR,
 				 "error parsing header: %d\n", err);
@@ -370,6 +372,7 @@ static void p9_read_work(struct work_struct *work)
 	 */
 	if ((m->req) && (m->rc.offset == m->rc.capacity)) {
 		p9_debug(P9_DEBUG_TRANS, "got new packet\n");
+		m->req->rc->size = m->rc.offset;
 		spin_lock(&m->client->lock);
 		if (m->req->status != REQ_STATUS_ERROR)
 			status = REQ_STATUS_RCVD;

net/9p/trans_rdma.c

@@ -320,6 +320,7 @@ recv_done(struct ib_cq *cq, struct ib_wc *wc)
 	if (wc->status != IB_WC_SUCCESS)
 		goto err_out;
 
+	c->rc->size = wc->byte_len;
 	err = p9_parse_header(c->rc, NULL, NULL, &tag, 1);
 	if (err)
 		goto err_out;

net/9p/trans_virtio.c

@@ -156,8 +156,10 @@ static void req_done(struct virtqueue *vq)
 			need_wakeup = true;
 		}
 
-		if (len)
+		if (len) {
+			req->rc->size = len;
 			p9_client_cb(chan->client, req, REQ_STATUS_RCVD);
+		}
 	}
 	spin_unlock_irqrestore(&chan->lock, flags);
 	/* Wakeup if anyone waiting for VirtIO ring space. */