[PATCH] btrfs: add 32-bit compat ioctl for BTRFS_IOC_GET_SUBVOL_INFO

[Daan De Meyer <daan@amutable.com>]

On 64-bit kernels with 32-bit userspace, struct btrfs_ioctl_timespec is
laid out as 16 bytes (8B sec + 4B nsec + 4B trailing padding) instead of
the 12 bytes a 32-bit userspace expects, because the surrounding struct
is not packed. As a result, struct btrfs_ioctl_get_subvol_info_args has
a different size and layout in 32-bit userspace than in the 64-bit
kernel, and BTRFS_IOC_GET_SUBVOL_INFO returns garbage to 32-bit callers.

Mirror what was done for BTRFS_IOC_SET_RECEIVED_SUBVOL: add a packed
btrfs_ioctl_get_subvol_info_args_32 with btrfs_ioctl_timespec_32 fields,
define BTRFS_IOC_GET_SUBVOL_INFO_32 with that struct as the size
argument, factor the existing handler into a shared _btrfs_ioctl_get_
subvol_info() helper, and add btrfs_ioctl_get_subvol_info_32() which
fills the kernel struct and translates field-by-field into the 32-bit
struct before copy_to_user().

Signed-off-by: Daan De Meyer <daan@amutable.com>
---
 fs/btrfs/ioctl.c | 112 +++++++++++++++++++++++++++++++++++++++++------
 1 file changed, 99 insertions(+), 13 deletions(-)

diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c
index a39460bf68a7..31be2590f1b2 100644
--- a/fs/btrfs/ioctl.c
+++ b/fs/btrfs/ioctl.c
@@ -82,6 +82,30 @@ struct btrfs_ioctl_received_subvol_args_32 {
 
 #define BTRFS_IOC_SET_RECEIVED_SUBVOL_32 _IOWR(BTRFS_IOCTL_MAGIC, 37, \
 				struct btrfs_ioctl_received_subvol_args_32)
+
+struct btrfs_ioctl_get_subvol_info_args_32 {
+	__u64 treeid;
+	char name[BTRFS_VOL_NAME_MAX + 1];
+	__u64 parent_id;
+	__u64 dirid;
+	__u64 generation;
+	__u64 flags;
+	__u8 uuid[BTRFS_UUID_SIZE];
+	__u8 parent_uuid[BTRFS_UUID_SIZE];
+	__u8 received_uuid[BTRFS_UUID_SIZE];
+	__u64 ctransid;
+	__u64 otransid;
+	__u64 stransid;
+	__u64 rtransid;
+	struct btrfs_ioctl_timespec_32 ctime;
+	struct btrfs_ioctl_timespec_32 otime;
+	struct btrfs_ioctl_timespec_32 stime;
+	struct btrfs_ioctl_timespec_32 rtime;
+	__u64 reserved[8];
+} __attribute__ ((__packed__));
+
+#define BTRFS_IOC_GET_SUBVOL_INFO_32 _IOR(BTRFS_IOCTL_MAGIC, 60, \
+				struct btrfs_ioctl_get_subvol_info_args_32)
 #endif
 
 #if defined(CONFIG_64BIT) && defined(CONFIG_COMPAT)
@@ -1945,9 +1969,9 @@ static int btrfs_ioctl_ino_lookup_user(struct file *file, void __user *argp)
 }
 
 /* Get the subvolume information in BTRFS_ROOT_ITEM and BTRFS_ROOT_BACKREF */
-static int btrfs_ioctl_get_subvol_info(struct inode *inode, void __user *argp)
+static int _btrfs_ioctl_get_subvol_info(struct inode *inode,
+					struct btrfs_ioctl_get_subvol_info_args *subvol_info)
 {
-	struct btrfs_ioctl_get_subvol_info_args *subvol_info;
 	struct btrfs_fs_info *fs_info;
 	struct btrfs_root *root;
 	struct btrfs_path *path;
@@ -1964,12 +1988,6 @@ static int btrfs_ioctl_get_subvol_info(struct inode *inode, void __user *argp)
 	if (!path)
 		return -ENOMEM;
 
-	subvol_info = kzalloc_obj(*subvol_info);
-	if (!subvol_info) {
-		btrfs_free_path(path);
-		return -ENOMEM;
-	}
-
 	fs_info = BTRFS_I(inode)->root->fs_info;
 
 	/* Get root_item of inode's subvolume */
@@ -2048,15 +2066,79 @@ static int btrfs_ioctl_get_subvol_info(struct inode *inode, void __user *argp)
 		}
 	}
 
-	btrfs_free_path(path);
-	path = NULL;
-	if (copy_to_user(argp, subvol_info, sizeof(*subvol_info)))
-		ret = -EFAULT;
-
 out:
 	btrfs_put_root(root);
 out_free:
 	btrfs_free_path(path);
+	return ret;
+}
+
+#ifdef CONFIG_64BIT
+static int btrfs_ioctl_get_subvol_info_32(struct inode *inode, void __user *argp)
+{
+	struct btrfs_ioctl_get_subvol_info_args *subvol_info = NULL;
+	struct btrfs_ioctl_get_subvol_info_args_32 *subvol_info_32 = NULL;
+	int ret;
+
+	subvol_info = kzalloc_obj(*subvol_info);
+	if (!subvol_info)
+		return -ENOMEM;
+
+	subvol_info_32 = kzalloc_obj(*subvol_info_32);
+	if (!subvol_info_32) {
+		ret = -ENOMEM;
+		goto out;
+	}
+
+	ret = _btrfs_ioctl_get_subvol_info(inode, subvol_info);
+	if (ret)
+		goto out;
+
+	subvol_info_32->treeid = subvol_info->treeid;
+	memcpy(subvol_info_32->name, subvol_info->name, sizeof(subvol_info_32->name));
+	subvol_info_32->parent_id = subvol_info->parent_id;
+	subvol_info_32->dirid = subvol_info->dirid;
+	subvol_info_32->generation = subvol_info->generation;
+	subvol_info_32->flags = subvol_info->flags;
+	memcpy(subvol_info_32->uuid, subvol_info->uuid, BTRFS_UUID_SIZE);
+	memcpy(subvol_info_32->parent_uuid, subvol_info->parent_uuid, BTRFS_UUID_SIZE);
+	memcpy(subvol_info_32->received_uuid, subvol_info->received_uuid, BTRFS_UUID_SIZE);
+	subvol_info_32->ctransid = subvol_info->ctransid;
+	subvol_info_32->otransid = subvol_info->otransid;
+	subvol_info_32->stransid = subvol_info->stransid;
+	subvol_info_32->rtransid = subvol_info->rtransid;
+	subvol_info_32->ctime.sec = subvol_info->ctime.sec;
+	subvol_info_32->ctime.nsec = subvol_info->ctime.nsec;
+	subvol_info_32->otime.sec = subvol_info->otime.sec;
+	subvol_info_32->otime.nsec = subvol_info->otime.nsec;
+	subvol_info_32->stime.sec = subvol_info->stime.sec;
+	subvol_info_32->stime.nsec = subvol_info->stime.nsec;
+	subvol_info_32->rtime.sec = subvol_info->rtime.sec;
+	subvol_info_32->rtime.nsec = subvol_info->rtime.nsec;
+
+	if (copy_to_user(argp, subvol_info_32, sizeof(*subvol_info_32)))
+		ret = -EFAULT;
+
+out:
+	kfree(subvol_info_32);
+	kfree(subvol_info);
+	return ret;
+}
+#endif
+
+static int btrfs_ioctl_get_subvol_info(struct inode *inode, void __user *argp)
+{
+	struct btrfs_ioctl_get_subvol_info_args *subvol_info;
+	int ret;
+
+	subvol_info = kzalloc_obj(*subvol_info);
+	if (!subvol_info)
+		return -ENOMEM;
+
+	ret = _btrfs_ioctl_get_subvol_info(inode, subvol_info);
+	if (!ret && copy_to_user(argp, subvol_info, sizeof(*subvol_info)))
+		ret = -EFAULT;
+
 	kfree(subvol_info);
 	return ret;
 }
@@ -5273,6 +5355,10 @@ long btrfs_ioctl(struct file *file, unsigned int
 		return btrfs_ioctl_set_features(file, argp);
 	case BTRFS_IOC_GET_SUBVOL_INFO:
 		return btrfs_ioctl_get_subvol_info(inode, argp);
+#ifdef CONFIG_64BIT
+	case BTRFS_IOC_GET_SUBVOL_INFO_32:
+		return btrfs_ioctl_get_subvol_info_32(inode, argp);
+#endif
 	case BTRFS_IOC_GET_SUBVOL_ROOTREF:
 		return btrfs_ioctl_get_subvol_rootref(root, argp);
 	case BTRFS_IOC_INO_LOOKUP_USER:
-- 
2.54.0