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>

4 files changed, 24 insertions, 11 deletions

diff --git a/net/9p/client.c b/net/9p/client.c
index 33717b1b84d8..20088aa06343 100644
--- a/net/9p/client.c
+++ b/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.
diff --git a/net/9p/trans_fd.c b/net/9p/trans_fd.c
index cce41b20a709..964260265b13 100644
--- a/net/9p/trans_fd.c
+++ b/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;
diff --git a/net/9p/trans_rdma.c b/net/9p/trans_rdma.c
index 3d414acb7015..2649b2ebf961 100644
--- a/net/9p/trans_rdma.c
+++ b/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;
diff --git a/net/9p/trans_virtio.c b/net/9p/trans_virtio.c
index d422bfc81eca..06dcd3cc6a29 100644
--- a/net/9p/trans_virtio.c
+++ b/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. */