Hi Nicholas,
I just noticed this problem in the interface:
+#include <linux/vhost.h>
+
+/*
+ * Used by QEMU userspace to ensure a consistent vhost-scsi ABI.
+ *
+ * ABI Rev 0: July 2012 version starting point for v3.6-rc merge
candidate +
+ * RFC-v2 vhost-scsi userspace. Add GET_ABI_VERSION ioctl
usage
+ */
+
+#define VHOST_SCSI_ABI_VERSION 0
+
+struct vhost_scsi_target {
+ int abi_version;
+ unsigned char vhost_wwpn[TRANSPORT_IQN_LEN];
+ unsigned short vhost_tpgt;
+};
+
Here TRANSPORT_IQN_LEN is 224, which is a multiple of 4.
Since vhost_tpgt is 2 bytes and abi_version is 4, the total size would
be 230. But gcc needs struct size be aligned to first field size, which
is 4 bytes, so it pads the structure by extra 2 bytes to the total of
232.
This padding is very undesirable in an ABI:
- it can not be initialized easily
- it can not be checked easily
- it can leak information between kernel and userspace
Simplest solution is probably just to make the padding
explicit:
+struct vhost_scsi_target {
+ int abi_version;
+ unsigned char vhost_wwpn[TRANSPORT_IQN_LEN];
+ unsigned short vhost_tpgt;
+ unsigned short reserved;
+};
+
I think we should fix this buglet before it goes out to users.
--
MST
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