9pfs: fix file descriptor leak

The v9fs_create() and v9fs_lcreate() functions are used to create a file
on the backend and to associate it to a fid. The fid shouldn't be already
in-use, otherwise both functions may silently leak a file descriptor or
allocated memory. The current code doesn't check that.

This patch ensures that the fid isn't already associated to anything
before using it.
Signed-off-by: NLi Qiang <liqiang6-s@360.cn>
(reworded the changelog, Greg Kurz)
Signed-off-by: NGreg Kurz <groug@kaod.org>

hw/9pfs/9p.c

@@ -1550,6 +1550,10 @@ static void coroutine_fn v9fs_lcreate(void *opaque)
         err = -ENOENT;
         goto out_nofid;
     }
+    if (fidp->fid_type != P9_FID_NONE) {
+        err = -EINVAL;
+        goto out;
+    }
 
     flags = get_dotl_openflags(pdu->s, flags);
     err = v9fs_co_open2(pdu, fidp, &name, gid,
@@ -2153,6 +2157,10 @@ static void coroutine_fn v9fs_create(void *opaque)
         err = -EINVAL;
         goto out_nofid;
     }
+    if (fidp->fid_type != P9_FID_NONE) {
+        err = -EINVAL;
+        goto out;
+    }
     if (perm & P9_STAT_MODE_DIR) {
         err = v9fs_co_mkdir(pdu, fidp, &name, perm & 0777,
                             fidp->uid, -1, &stbuf);