From: Christian Schoenebeck <qemu_oss@crudebyte.com>
Date: Tue, 16 Jun 2026 15:00:11 +0000 (+0200)
Subject: hw/9pfs: fix invalid union access by v9fs_co_fstat()
X-Git-Tag: v11.1.0-rc0~39^2~1
X-Git-Url: http://git.ipfire.org/gitweb.cgi?a=commitdiff_plain;h=c3aa2491cd2cd89e2f484d32f323ee447e782984;p=thirdparty%2Fqemu.git

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 a2b7335515..3119f01117 100644
--- 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;