Re: [RFC] Add option to mount only a pids subset
From: Oleg Nesterov <hidden>
Date: 2017-03-23 16:07:16
Also in:
lkml
Possibly related (same subject, not in this thread)
- 2017-03-09 · Re: [RFC] Add option to mount only a pids subset · Eric W. Biederman <hidden>
Again, I can't really review this, I know nothing about vfs, but since nobody else replied... On 03/20, Alexey Gladkov wrote:
quoted hunk ↗ jump to hunk
@@ -97,7 +169,23 @@ static struct dentry *proc_mount(struct file_system_type *fs_type, ns = task_active_pid_ns(current); } - return mount_ns(fs_type, flags, data, ns, ns->user_ns, proc_fill_super); + root = mount_ns(fs_type, flags, data, ns, ns->user_ns, proc_fill_super); + + if (!IS_ERR(root)) { + if (!proc_fill_options(data, &opts)) + return ERR_PTR(-EINVAL);
So we have to call proc_fill_options() twice, not good... Yes, I understand why, but perhaps we factor it out somehow, we can pack options + pid_ns into sb->s_fs_info. Nevermind, this is minor.
+ if (opts.pid_only) {
+ int ret;
+
+ if (!ns->pidfs && (ret = fill_pidfs_root(root->d_sb)))
+ return ERR_PTR(ret);
+
+ root = ns->pidfs;Afaics this lacks dget(ns->pidfs) which should pair with dput(mnt.mnt_root) in cleanup_mnt(). IIUC otherwise ns->pidfs can go away after umount, OTOH, if we return ns->pidfs then dget(sb->s_root) in mount_ns() is not balanced. But this all is fixeable. So with this change "mount -opidonly" creates another IS_ROOT() dentry which is not equal to sb->s_root. I simply do not know if this is technically correct or not... but, say, the "Only bind mounts can have disconnected paths" comment in path_connected() makes me worry ;) And this obviously means that /path-to-pidonly-mnt/ won't share dentries with the normal /proc mount. Not really good imo even if not really wrong... Lets look at proc_flush_task(). The exiting task will flush its $pid dentries in /proc/ but not in /path-to-pidonly-mnt/ iiuc. Again, not really a bug, but still... Oleg.