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[Qemu-block] [PATCH] block/qdev: Fix NULL access when using BB twice

From: Kevin Wolf
Subject: [Qemu-block] [PATCH] block/qdev: Fix NULL access when using BB twice
Date: Thu, 23 Jun 2016 09:30:01 +0200

BlockBackend has only a single pointer to its guest device, so it makes
sure that only a single guest device is attached to it. device-add
returns an error if you try to attach a second device to a BB. In order
to make the error message nicer, -device that manually connects to a
if=none block device get a different message than -drive that implicitly
creates a guest device. The if=... option is stored in DriveInfo.

However, since blockdev-add exists, not every BlockBackend has a
DriveInfo any more. Check that it exists before we dereference it.

QMP reproducer resulting in a segfault:


Signed-off-by: Kevin Wolf <address@hidden>
 hw/core/qdev-properties-system.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/hw/core/qdev-properties-system.c b/hw/core/qdev-properties-system.c
index 623be94..c5cc9cf 100644
--- a/hw/core/qdev-properties-system.c
+++ b/hw/core/qdev-properties-system.c
@@ -91,7 +91,7 @@ static void parse_drive(DeviceState *dev, const char *str, 
void **ptr,
     if (blk_attach_dev(blk, dev) < 0) {
         DriveInfo *dinfo = blk_legacy_dinfo(blk);
-        if (dinfo->type != IF_NONE) {
+        if (dinfo && dinfo->type != IF_NONE) {
             error_setg(errp, "Drive '%s' is already in use because "
                        "it has been automatically connected to another "
                        "device (did you need 'if=none' in the drive options?)",

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