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[Qemu-devel] [PATCH 099/108] Allow mismatched virtio config-len

From: Michael Roth
Subject: [Qemu-devel] [PATCH 099/108] Allow mismatched virtio config-len
Date: Wed, 6 Aug 2014 15:39:49 -0500

From: "Dr. David Alan Gilbert" <address@hidden>

Commit 'virtio: validate config_len on load' restricted config_len
loaded from the wire to match the config_len that the device had.

Unfortunately, there are cases where this isn't true, the one
we found it on was the wce addition in virtio-blk.

Allow mismatched config-lengths:
   *) If the version on the wire is shorter then fine
   *) If the version on the wire is longer, load what we have space
      for and skip the rest.

(This is address@hidden's rework of what I originally posted)

Signed-off-by: Dr. David Alan Gilbert <address@hidden>
Reviewed-by: Michael S. Tsirkin <address@hidden>
Signed-off-by: Michael S. Tsirkin <address@hidden>
(cherry picked from commit 2f5732e9648fcddc8759a8fd25c0b41a38352be6)
Signed-off-by: Michael Roth <address@hidden>
 hw/virtio/virtio.c | 16 +++++++++++-----
 1 file changed, 11 insertions(+), 5 deletions(-)

diff --git a/hw/virtio/virtio.c b/hw/virtio/virtio.c
index 3557c17..3e4b70c 100644
--- a/hw/virtio/virtio.c
+++ b/hw/virtio/virtio.c
@@ -926,12 +926,18 @@ int virtio_load(VirtIODevice *vdev, QEMUFile *f)
         return -1;
     config_len = qemu_get_be32(f);
-    if (config_len != vdev->config_len) {
-        error_report("Unexpected config length 0x%x. Expected 0x%zx",
-                     config_len, vdev->config_len);
-        return -1;
+    /*
+     * There are cases where the incoming config can be bigger or smaller
+     * than what we have; so load what we have space for, and skip
+     * any excess that's in the stream.
+     */
+    qemu_get_buffer(f, vdev->config, MIN(config_len, vdev->config_len));
+    while (config_len > vdev->config_len) {
+        qemu_get_byte(f);
+        config_len--;
-    qemu_get_buffer(f, vdev->config, vdev->config_len);
     num = qemu_get_be32(f);

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