Fix use-after-free after unmount

During unmount `zfsvfs` is destroyed and the pointer is zeroed in the VCB. There is however still a copy of the pointer in the DCB. Windows can still call into `zfs_AcquireForLazyWrite` through `CcMgr` after unmount and this would use the already freed `zfsvfs` pointer. To fix this we set the pointer to zero in the DCB and add a zero check in `zfs_AcquireForLazyWrite`. Signed-off-by: Axel Gembe <[email protected]>
openzfsonwindows · Oct 13, 2023 · 669adec · 669adec
1 parent fee66c7
commit 669adec
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diff --git a/module/os/windows/zfs/zfs_vnops_windows.c b/module/os/windows/zfs/zfs_vnops_windows.c
@@ -132,6 +132,16 @@ zfs_AcquireForLazyWrite(void *Context, BOOLEAN Wait)
 	struct vnode *vp = fo->FsContext;
 	dprintf("%s:fo %p\n", __func__, fo);
 
+	if ((zmo->vpb->Flags & VPB_MOUNTED) == 0) {
+		dprintf("%s:fo not mounted\n", __func__);
+		return (FALSE);
+	}
+
+	if (zfsvfs == NULL) {
+		dprintf("%s:fo already freed zfsvfs\n", __func__);
+		return (FALSE);
+	}
+
 	/* Confirm we are mounted, and stop unmounting */
 	if (vfs_busy(zfsvfs->z_vfs, 0) != 0)
 		return (FALSE);

diff --git a/module/os/windows/zfs/zfs_vnops_windows_mount.c b/module/os/windows/zfs/zfs_vnops_windows_mount.c
@@ -1583,6 +1583,12 @@ zfs_windows_unmount(zfs_cmd_t *zc)
 		if (error)
 			goto out_unlock;
 
+		if (zmo_dcb != NULL) {
+			// zfs_vfs_unmount already freed the zfsvfs, but
+			// a reference still exists in the DCB.
+			vfs_setfsprivate(zmo_dcb, NULL);
+		}
+
 		// Release devices
 		IoDeleteSymbolicLink(&zmo->symlink_name);