[PATCH 1/3] hw/9pfs: fix invalid union access by v9fs_co_fsync()

[Christian Schoenebeck]

The individual FID types (P9_FID_NONE, P9_FID_FILE, P9_FID_DIR, P9_FID_XATTR)
share union V9fsFidOpenState with FID-type specific fields. Accessing any of
the union fields must comply with the FID-type to avoid undefined behaviour
or information disclosure.

Fix this in v9fs_fsync() and v9fs_wstat() by checking if FID has a valid file
descriptor before calling v9fs_co_fsync().

Fixes: 10b468bdc533 ("virtio-9p: Implement TXATTRCREATE")
Reported-by: Feifan Qian <be...@proton.me>
Signed-off-by: Christian Schoenebeck <qemu_...@crudebyte.com>
---
 hw/9pfs/9p.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/hw/9pfs/9p.c b/hw/9pfs/9p.c
index b4314d2549..6dd6a57e7a 100644
--- a/hw/9pfs/9p.c
+++ b/hw/9pfs/9p.c
@@ -2247,10 +2247,15 @@ static void coroutine_fn v9fs_fsync(void *opaque)
         err = -ENOENT;
         goto out_nofid;
     }
+    if (!fid_has_valid_file_handle(pdu->s, fidp)) {
+        err = -EBADF;
+        goto out;
+    }
     err = v9fs_co_fsync(pdu, fidp, datasync);
     if (!err) {
         err = offset;
     }
+out:
     put_fid(pdu, fidp);
 out_nofid:
     pdu_complete(pdu, err);
@@ -3584,6 +3589,10 @@ static void coroutine_fn v9fs_wstat(void *opaque)
     }
     /* do we need to sync the file? */
     if (donttouch_stat(&v9stat)) {
+        if (!fid_has_valid_file_handle(s, fidp)) {
+            err = -EBADF;
+            goto out;
+        }
         err = v9fs_co_fsync(pdu, fidp, 0);
         goto out;
     }
-- 
2.47.3