hw/9pfs: fix invalid union access by v9fs_co_fstat()

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_lock() and v9fs_getlock() by checking if FID has a valid
file descriptor before calling v9fs_co_fstat().

Fixes: 10b468bdc533 ("virtio-9p: Implement TXATTRCREATE")
Link: https://lore.kernel.org/qemu-devel/4b33cd1aaa2551efda220a6f651e3660d27f4746.1781621428.git.qemu_oss@crudebyte.com
Signed-off-by: Christian Schoenebeck <qemu_oss@crudebyte.com>

diff --git a/hw/9pfs/9p.c b/hw/9pfs/9p.c
index a2b73355152bf6e98ff1275d1672b545a5a0c201..3119f011173d85304d2c9198a0a576aff2fcd587 100644 (file)
--- a/hw/9pfs/9p.c
+++ b/hw/9pfs/9p.c
@@ -3908,6 +3908,10 @@ static void coroutine_fn v9fs_lock(void *opaque)
         err = -ENOENT;
         goto out_nofid;
     }
+    if (!fid_has_valid_file_handle(pdu->s, fidp)) {
+        err = -EBADF;
+        goto out;
+    }
     err = v9fs_co_fstat(pdu, fidp, &stbuf);
     if (err < 0) {
         goto out;
@@ -3953,6 +3957,10 @@ static void coroutine_fn v9fs_getlock(void *opaque)
         err = -ENOENT;
         goto out_nofid;
     }
+    if (!fid_has_valid_file_handle(pdu->s, fidp)) {
+        err = -EBADF;
+        goto out;
+    }
     err = v9fs_co_fstat(pdu, fidp, &stbuf);
     if (err < 0) {
         goto out;