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Btrfs: prevent loops in the directory tree when creating snapshots

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For a directory tree:

/mnt/subvolA/subvolB

btrfsctl -s /mnt/subvolA/subvolB /mnt

Will create a directory loop with subvolA under subvolB.  This
commit uses the forward refs for each subvol and snapshot to error out
before creating the loop.

Signed-off-by: Chris Mason <chris.mason@oracle.com>
This commit is contained in:
Chris Mason
2008-11-17 21:14:24 -05:00
parent 0660b5af3f
commit ea9e8b11bd
4 changed files with 73 additions and 1 deletions
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50
fs/btrfs/ioctl.c
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@@ -284,6 +284,56 @@ static noinline int btrfs_mksubvol(struct path *parent, char *name,
* subvolume with specific mode bits.
*/
if (snap_src) {
struct dentry *dir = dentry->d_parent;
struct dentry *test = dir->d_parent;
struct btrfs_path *path = btrfs_alloc_path();
int ret;
u64 test_oid;
u64 parent_oid = BTRFS_I(dir->d_inode)->root->root_key.objectid;
test_oid = snap_src->root_key.objectid;
ret = btrfs_find_root_ref(snap_src->fs_info->tree_root,
path, parent_oid, test_oid);
if (ret == 0)
goto create;
btrfs_release_path(snap_src->fs_info->tree_root, path);
/* we need to make sure we aren't creating a directory loop
* by taking a snapshot of something that has our current
* subvol in its directory tree. So, this loops through
* the dentries and checks the forward refs for each subvolume
* to see if is references the subvolume where we are
* placing this new snapshot.
*/
while(1) {
if (!test ||
dir == snap_src->fs_info->sb->s_root ||
test == snap_src->fs_info->sb->s_root ||
test->d_inode->i_sb != snap_src->fs_info->sb) {
break;
}
if (S_ISLNK(test->d_inode->i_mode)) {
printk("Symlink in snapshot path, failed\n");
error = -EMLINK;
btrfs_free_path(path);
goto out_drop_write;
}
test_oid =
BTRFS_I(test->d_inode)->root->root_key.objectid;
ret = btrfs_find_root_ref(snap_src->fs_info->tree_root,
path, test_oid, parent_oid);
if (ret == 0) {
printk("Snapshot creation failed, looping\n");
error = -EMLINK;
btrfs_free_path(path);
goto out_drop_write;
}
btrfs_release_path(snap_src->fs_info->tree_root, path);
test = test->d_parent;
}
create:
btrfs_free_path(path);
error = create_snapshot(snap_src, dentry, name, namelen);
} else {
error = create_subvol(BTRFS_I(parent->dentry->d_inode)->root,