[PATCHv2 3/4] staging: android: ion: Add an ioctl for ABI checking

[Laura Abbott <labbott@redhat.com>]

The current Ion ioctls lack a good way to tell what ioctls are
available. Introduce an ioctl to give an ABI version. This way when the
ABI inevitably gets screwed up userspace will have a way to tell what
version of the screw up is available.

Signed-off-by: Laura Abbott <labbott@redhat.com>
---
 drivers/staging/android/ion/ion-ioctl.c | 53 ++++++++++++++++++++++++++-------
 drivers/staging/android/uapi/ion.h      | 22 ++++++++++++++
 2 files changed, 65 insertions(+), 10 deletions(-)

diff --git a/drivers/staging/android/ion/ion-ioctl.c b/drivers/staging/android/ion/ion-ioctl.c
index 341ba7d..53b9520 100644
--- a/drivers/staging/android/ion/ion-ioctl.c
+++ b/drivers/staging/android/ion/ion-ioctl.c
@@ -22,6 +22,29 @@
 #include "ion_priv.h"
 #include "compat_ion.h"
 
+union ion_ioctl_arg {
+	struct ion_fd_data fd;
+	struct ion_allocation_data allocation;
+	struct ion_handle_data handle;
+	struct ion_custom_data custom;
+	struct ion_abi_version abi_version;
+};
+
+static int validate_ioctl_arg(unsigned int cmd, union ion_ioctl_arg *arg)
+{
+	int ret = 0;
+
+	switch (cmd) {
+	case ION_IOC_ABI_VERSION:
+		ret = arg->abi_version.reserved != 0;
+		break;
+	default:
+		break;
+	}
+
+	return ret ? -EINVAL : 0;
+}
+
 /* fix up the cases where the ioctl direction bits are incorrect */
 static unsigned int ion_ioctl_dir(unsigned int cmd)
 {
@@ -42,22 +65,27 @@ long ion_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
 	struct ion_handle *cleanup_handle = NULL;
 	int ret = 0;
 	unsigned int dir;
-
-	union {
-		struct ion_fd_data fd;
-		struct ion_allocation_data allocation;
-		struct ion_handle_data handle;
-		struct ion_custom_data custom;
-	} data;
+	union ion_ioctl_arg data;
 
 	dir = ion_ioctl_dir(cmd);
 
 	if (_IOC_SIZE(cmd) > sizeof(data))
 		return -EINVAL;
 
-	if (dir & _IOC_WRITE)
-		if (copy_from_user(&data, (void __user *)arg, _IOC_SIZE(cmd)))
-			return -EFAULT;
+	/*
+	 * The copy_from_user is unconditional here for both read and write
+	 * to do the validate. If there is no write for the ioctl, the
+	 * buffer is cleared
+	 */
+	if (copy_from_user(&data, (void __user *)arg, _IOC_SIZE(cmd)))
+		return -EFAULT;
+
+	ret = validate_ioctl_arg(cmd, &data);
+	if (WARN_ON_ONCE(ret))
+		return ret;
+
+	if (!(dir & _IOC_WRITE))
+		memset(&data, 0, sizeof(data));
 
 	switch (cmd) {
 	case ION_IOC_ALLOC:
@@ -129,6 +157,11 @@ long ion_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
 						data.custom.arg);
 		break;
 	}
+	case ION_IOC_ABI_VERSION:
+	{
+		data.abi_version.abi_version = ION_ABI_VERSION;
+		break;
+	}
 	default:
 		return -ENOTTY;
 	}
diff --git a/drivers/staging/android/uapi/ion.h b/drivers/staging/android/uapi/ion.h
index a9c4e8b..7ca4e8b 100644
--- a/drivers/staging/android/uapi/ion.h
+++ b/drivers/staging/android/uapi/ion.h
@@ -19,6 +19,7 @@
 
 #include <linux/ioctl.h>
 #include <linux/types.h>
+#include <linux/version.h>
 
 typedef int ion_user_handle_t;
 
@@ -128,6 +129,19 @@ struct ion_custom_data {
 	unsigned long arg;
 };
 
+/**
+ * struct ion_abi_version
+ *
+ *  @version - current ABI version
+ */
+
+#define ION_ABI_VERSION                KERNEL_VERSION(0, 1, 0)
+
+struct ion_abi_version {
+	__u32 abi_version;
+	__u32 reserved;
+};
+
 #define ION_IOC_MAGIC		'I'
 
 /**
@@ -194,4 +208,12 @@ struct ion_custom_data {
  */
 #define ION_IOC_CUSTOM		_IOWR(ION_IOC_MAGIC, 6, struct ion_custom_data)
 
+/**
+ * DOC: ION_IOC_ABI_VERSION - return ABI version
+ *
+ * Returns the ABI version of this driver.
+ */
+#define ION_IOC_ABI_VERSION    _IOR(ION_IOC_MAGIC, 8, \
+					struct ion_abi_version)
+
 #endif /* _UAPI_LINUX_ION_H */
-- 
2.7.4