9pfs: handle transport errors in pdu_complete()

Contrary to what is written in the comment, a buggy guest can misconfigure
the transport buffers and pdu_marshal() may return an error.  If this ever
happens, it is up to the transport layer to handle the situation (9P is
transport agnostic).

This fixes Coverity issue CID1348518.

Signed-off-by: Greg Kurz <groug@kaod.org>
Reviewed-by: Stefano Stabellini <sstabellini@kernel.org>

1 files changed, 15 insertions, 8 deletions

diff --git a/hw/9pfs/9p.c b/hw/9pfs/9p.c
index 8e5cac71eb..6c92bad5b3 100644
--- a/hw/9pfs/9p.c
+++ b/hw/9pfs/9p.c
@@ -624,15 +624,11 @@ void pdu_free(V9fsPDU *pdu)
     QLIST_INSERT_HEAD(&s->free_list, pdu, next);
 }
 
-/*
- * We don't do error checking for pdu_marshal/unmarshal here
- * because we always expect to have enough space to encode
- * error details
- */
 static void coroutine_fn pdu_complete(V9fsPDU *pdu, ssize_t len)
 {
     int8_t id = pdu->id + 1; /* Response */
     V9fsState *s = pdu->s;
+    int ret;
 
     if (len < 0) {
         int err = -len;
@@ -644,11 +640,19 @@ static void coroutine_fn pdu_complete(V9fsPDU *pdu, ssize_t len)
             str.data = strerror(err);
             str.size = strlen(str.data);
 
-            len += pdu_marshal(pdu, len, "s", &str);
+            ret = pdu_marshal(pdu, len, "s", &str);
+            if (ret < 0) {
+                goto out_notify;
+            }
+            len += ret;
             id = P9_RERROR;
         }
 
-        len += pdu_marshal(pdu, len, "d", err);
+        ret = pdu_marshal(pdu, len, "d", err);
+        if (ret < 0) {
+            goto out_notify;
+        }
+        len += ret;
 
         if (s->proto_version == V9FS_PROTO_2000L) {
             id = P9_RLERROR;
@@ -657,12 +661,15 @@ static void coroutine_fn pdu_complete(V9fsPDU *pdu, ssize_t len)
     }
 
     /* fill out the header */
-    pdu_marshal(pdu, 0, "dbw", (int32_t)len, id, pdu->tag);
+    if (pdu_marshal(pdu, 0, "dbw", (int32_t)len, id, pdu->tag) < 0) {
+        goto out_notify;
+    }
 
     /* keep these in sync */
     pdu->size = len;
     pdu->id = id;
 
+out_notify:
     pdu->s->transport->push_and_notify(pdu);
 
     /* Now wakeup anybody waiting in flush for this request */