[Qemu-devel] [PATCH] blockdev: Refuse to open encrypted image unless paused

[Markus Armbruster <armbru@redhat.com>]

Opening an encrypted image takes an additional step: setting the key.
Between open and the key set, the image must not be used.

We have some protection against accidental use in place: you can't
unpause a guest while we're missing keys.  You can, however, hot-plug
block devices lacking keys into a running guest just fine, or insert
media lacking keys.  In the latter case, notifying the guest of the
insert is delayed until the key is set, which may suffice to protect
at least some guests in common usage.

This patch makes the protection apply in more cases, in a rather
heavy-handed way: it doesn't let you open encrypted images unless
we're in a paused state.

It doesn't extend the protection to users other than the guest (block
jobs?).  Use of runstate_check() from block.c is disgusting.  Best I
can do right now.

Signed-off-by: Markus Armbruster <armbru@redhat.com>
---
 block.c                | 8 +++++++-
 stubs/Makefile.objs    | 1 +
 stubs/runstate-check.c | 6 ++++++
 3 files changed, 14 insertions(+), 1 deletion(-)
 create mode 100644 stubs/runstate-check.c

diff --git a/block.c b/block.c
index f1ef4b0..7604881 100644
--- a/block.c
+++ b/block.c
@@ -1388,12 +1388,18 @@ done:
         ret = -EINVAL;
         goto close_and_fail;
     }
-    QDECREF(options);
 
     if (!bdrv_key_required(bs)) {
         bdrv_dev_change_media_cb(bs, true);
+    } else if (!runstate_check(RUN_STATE_PRELAUNCH)
+            && !runstate_check(RUN_STATE_PAUSED)) { /* HACK */
+        error_setg(errp,
+                   "Guest must be stopped for opening of encrypted image");
+        ret = -EBUSY;
+        goto close_and_fail;
     }
 
+    QDECREF(options);
     *pbs = bs;
     return 0;
 
diff --git a/stubs/Makefile.objs b/stubs/Makefile.objs
index df3aa7a..09e7790 100644
--- a/stubs/Makefile.objs
+++ b/stubs/Makefile.objs
@@ -19,6 +19,7 @@ stub-obj-y += mon-protocol-event.o
 stub-obj-y += mon-set-error.o
 stub-obj-y += pci-drive-hot-add.o
 stub-obj-y += reset.o
+stub-obj-y += runstate-check.o
 stub-obj-y += set-fd-handler.o
 stub-obj-y += slirp.o
 stub-obj-y += sysbus.o
diff --git a/stubs/runstate-check.c b/stubs/runstate-check.c
new file mode 100644
index 0000000..bd2e375
--- /dev/null
+++ b/stubs/runstate-check.c
@@ -0,0 +1,6 @@
+#include "sysemu/sysemu.h"
+
+bool runstate_check(RunState state)
+{
+    return state == RUN_STATE_PRELAUNCH;
+}
-- 
1.8.1.4