nilfs2: allow future expansion of metadata read out via get info ioctl

Nilfs has some ioctl commands to read out metadata from meta data
files:

 - NILFS_IOCTL_GET_CPINFO for checkpoint file,
 - NILFS_IOCTL_GET_SUINFO for segment usage file, and
 - NILFS_IOCTL_GET_VINFO for Disk Address Transalation (DAT) file,
   respectively.

Every routine on these metadata files is implemented so that it allows
future expansion of on-disk format.  But, the above ioctl commands do
not support expansion even though nilfs_argv structure can handle
arbitrary size for data exchanged via ioctl.

This allows future expansion of the following structures which give
basic format of the "get information" ioctls:

 - struct nilfs_cpinfo
 - struct nilfs_suinfo
 - struct nilfs_vinfo

So, this introduces forward compatility of such ioctl commands.

In this patch, a sanity check in nilfs_ioctl_get_info() function is
changed to accept larger data structure [1], and metadata read
routines are rewritten so that they become compatible for larger
structures; the routines will just ignore the remaining fields which
the current version of nilfs doesn't know.

[1] The ioctl function already has another upper limit (PAGE_SIZE
    against a structure, which appears in nilfs_ioctl_wrap_copy
    function), and this will not cause security problem.

Signed-off-by: Ryusuke Konishi <konishi.ryusuke@lab.ntt.co.jp>

1 files changed, 5 insertions, 4 deletions

diff --git a/fs/nilfs2/ioctl.c b/fs/nilfs2/ioctl.c
index bdad7e4..6ea5f87 100644
--- a/fs/nilfs2/ioctl.c
+++ b/fs/nilfs2/ioctl.c
@@ -152,7 +152,7 @@ nilfs_ioctl_do_get_cpinfo(struct the_nilfs *nilfs, __u64 *posp, int flags,
 
 	down_read(&nilfs->ns_segctor_sem);
 	ret = nilfs_cpfile_get_cpinfo(nilfs->ns_cpfile, posp, flags, buf,
-				      nmembs);
+				      size, nmembs);
 	up_read(&nilfs->ns_segctor_sem);
 	return ret;
 }
@@ -182,7 +182,8 @@ nilfs_ioctl_do_get_suinfo(struct the_nilfs *nilfs, __u64 *posp, int flags,
 	int ret;
 
 	down_read(&nilfs->ns_segctor_sem);
-	ret = nilfs_sufile_get_suinfo(nilfs->ns_sufile, *posp, buf, nmembs);
+	ret = nilfs_sufile_get_suinfo(nilfs->ns_sufile, *posp, buf, size,
+				      nmembs);
 	up_read(&nilfs->ns_segctor_sem);
 	return ret;
 }
@@ -212,7 +213,7 @@ nilfs_ioctl_do_get_vinfo(struct the_nilfs *nilfs, __u64 *posp, int flags,
 	int ret;
 
 	down_read(&nilfs->ns_segctor_sem);
-	ret = nilfs_dat_get_vinfo(nilfs_dat_inode(nilfs), buf, nmembs);
+	ret = nilfs_dat_get_vinfo(nilfs_dat_inode(nilfs), buf, size, nmembs);
 	up_read(&nilfs->ns_segctor_sem);
 	return ret;
 }
@@ -589,7 +590,7 @@ static int nilfs_ioctl_get_info(struct inode *inode, struct file *filp,
 	if (copy_from_user(&argv, argp, sizeof(argv)))
 		return -EFAULT;
 
-	if (argv.v_size != membsz)
+	if (argv.v_size < membsz)
 		return -EINVAL;
 
 	ret = nilfs_ioctl_wrap_copy(nilfs, &argv, _IOC_DIR(cmd), dofunc);