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, 21 insertions, 12 deletions

diff --git a/fs/nilfs2/cpfile.c b/fs/nilfs2/cpfile.c
index 300f1cdfa862..b5a8cd6b474f 100644
--- a/fs/nilfs2/cpfile.c
+++ b/fs/nilfs2/cpfile.c
@@ -384,9 +384,10 @@ static void nilfs_cpfile_checkpoint_to_cpinfo(struct inode *cpfile,
 }
 
 static ssize_t nilfs_cpfile_do_get_cpinfo(struct inode *cpfile, __u64 *cnop,
-                                          struct nilfs_cpinfo *ci, size_t nci)
+                                          void *buf, unsigned cisz, size_t nci)
 {
         struct nilfs_checkpoint *cp;
+        struct nilfs_cpinfo *ci = buf;
         struct buffer_head *bh;
         size_t cpsz = NILFS_MDT(cpfile)->mi_entry_size;
         __u64 cur_cno = nilfs_mdt_cno(cpfile), cno = *cnop;
@@ -410,17 +411,22 @@ static ssize_t nilfs_cpfile_do_get_cpinfo(struct inode *cpfile, __u64 *cnop,
                 kaddr = kmap_atomic(bh->b_page, KM_USER0);
                 cp = nilfs_cpfile_block_get_checkpoint(cpfile, cno, bh, kaddr);
                 for (i = 0; i < ncps && n < nci; i++, cp = (void *)cp + cpsz) {
-                        if (!nilfs_checkpoint_invalid(cp))
-                                nilfs_cpfile_checkpoint_to_cpinfo(
-                                        cpfile, cp, &ci[n++]);
+                        if (!nilfs_checkpoint_invalid(cp)) {
+                                nilfs_cpfile_checkpoint_to_cpinfo(cpfile, cp,
+                                                                  ci);
+                                ci = (void *)ci + cisz;
+                                n++;
+                        }
                 }
                 kunmap_atomic(kaddr, KM_USER0);
                 brelse(bh);
         }
 
         ret = n;
-        if (n > 0)
-                *cnop = ci[n - 1].ci_cno + 1;
+        if (n > 0) {
+                ci = (void *)ci - cisz;
+                *cnop = ci->ci_cno + 1;
+        }
 
  out:
         up_read(&NILFS_MDT(cpfile)->mi_sem);
@@ -428,11 +434,12 @@ static ssize_t nilfs_cpfile_do_get_cpinfo(struct inode *cpfile, __u64 *cnop,
 }
 
 static ssize_t nilfs_cpfile_do_get_ssinfo(struct inode *cpfile, __u64 *cnop,
-                                          struct nilfs_cpinfo *ci, size_t nci)
+                                          void *buf, unsigned cisz, size_t nci)
 {
         struct buffer_head *bh;
         struct nilfs_cpfile_header *header;
         struct nilfs_checkpoint *cp;
+        struct nilfs_cpinfo *ci = buf;
         __u64 curr = *cnop, next;
         unsigned long curr_blkoff, next_blkoff;
         void *kaddr;
@@ -472,7 +479,9 @@ static ssize_t nilfs_cpfile_do_get_ssinfo(struct inode *cpfile, __u64 *cnop,
                 if (unlikely(nilfs_checkpoint_invalid(cp) ||
                              !nilfs_checkpoint_snapshot(cp)))
                         break;
-                nilfs_cpfile_checkpoint_to_cpinfo(cpfile, cp, &ci[n++]);
+                nilfs_cpfile_checkpoint_to_cpinfo(cpfile, cp, ci);
+                ci = (void *)ci + cisz;
+                n++;
                 next = le64_to_cpu(cp->cp_snapshot_list.ssl_next);
                 if (next == 0)
                         break; /* reach end of the snapshot list */
@@ -511,13 +520,13 @@ static ssize_t nilfs_cpfile_do_get_ssinfo(struct inode *cpfile, __u64 *cnop,
  */
 
 ssize_t nilfs_cpfile_get_cpinfo(struct inode *cpfile, __u64 *cnop, int mode,
-                                struct nilfs_cpinfo *ci, size_t nci)
+                                void *buf, unsigned cisz, size_t nci)
 {
         switch (mode) {
         case NILFS_CHECKPOINT:
-                return nilfs_cpfile_do_get_cpinfo(cpfile, cnop, ci, nci);
+                return nilfs_cpfile_do_get_cpinfo(cpfile, cnop, buf, cisz, nci);
         case NILFS_SNAPSHOT:
-                return nilfs_cpfile_do_get_ssinfo(cpfile, cnop, ci, nci);
+                return nilfs_cpfile_do_get_ssinfo(cpfile, cnop, buf, cisz, nci);
         default:
                 return -EINVAL;
         }
@@ -535,7 +544,7 @@ int nilfs_cpfile_delete_checkpoint(struct inode *cpfile, __u64 cno)
         ssize_t nci;
         int ret;
 
-        nci = nilfs_cpfile_do_get_cpinfo(cpfile, &tcno, &ci, 1);
+        nci = nilfs_cpfile_do_get_cpinfo(cpfile, &tcno, &ci, sizeof(ci), 1);
         if (nci < 0)
                 return nci;
         else if (nci == 0 || ci.ci_cno != cno)