From: Amir Goldstein <amir73il@gmail.com>
To: Al Viro <viro@zeniv.linux.org.uk>,
Christian Brauner <christian.brauner@ubuntu.com>,
Miklos Szeredi <miklos@szeredi.hu>
Cc: Jan Kara <jack@suse.cz>,
linux-fsdevel <linux-fsdevel@vger.kernel.org>,
"J. Bruce Fields" <bfields@fieldses.org>
Subject: Re: fsnotify path hooks
Date: Tue, 20 Apr 2021 01:04:29 +0300 [thread overview]
Message-ID: <CAOQ4uxhXXLwUBr01zuU=Uo9rzEg4JQ2w_zEejdRRU8FSJsJg0w@mail.gmail.com> (raw)
In-Reply-To: <YH23mMawq2nZeBhk@zeniv-ca.linux.org.uk>
On Mon, Apr 19, 2021 at 8:02 PM Al Viro <viro@zeniv.linux.org.uk> wrote:
>
> On Mon, Apr 19, 2021 at 07:41:51PM +0300, Amir Goldstein wrote:
>
> > Would you be willing to make an exception for notify_change()
> > and pass mnt arg to the helper? and if so, which of the following
> > is the lesser evil in your opinion:
> >
> > 1. Optional mnt arg
> > --------------------------
> > int notify_change(struct vfsmount *mnt,
> > struct user_namespace *mnt_userns,
> > struct dentry *dentry, struct iattr *attr,
> > struct inode **delegated_inode)
> >
> > @mnt is non-NULL from syscalls and nfsd and NULL from other callers.
> >
> > 2. path instead of dentry
> > --------------------------------
> > int notify_change(struct user_namespace *mnt_userns,
> > struct path *path, struct iattr *attr,
> > struct inode **delegated_inode)
> >
> > This is symmetric with vfs_getattr().
> > syscalls and nfsd use the actual path.
> > overlayfs, ecryptfs, cachefiles compose a path from the private mount
> > (Christian posted patches to make ecryptfs, cachefiles mount private).
> >
> > 3. Mandatory mnt arg
> > -----------------------------
> > Like #1, but use some private mount instead of NULL, similar to the
> > mnt_userns arg.
> >
> > Any of the above acceptable?
> >
> > Pushed option #1 (along with rest of the work) to:
> > https://github.com/amir73il/linux/commits/fsnotify_path_hooks
> >
> > It's only sanity tested.
>
> Out of that bunch only #2 is more or less tolerable.
Tolerable works for me.
> HOWEVER, if we go that way, mnt_user_ns crap must go, and
Christian requested that I refrain from re-acquiring mnt_user_ns
from mnt after it had already been used for security checks,
for example:
do_open()
may_create_in_sticky(mnt_userns,...)
may_open(mnt_userns,...)
handle_truncate(mnt_userns,...
do_truncate(mnt_userns,...
notify_change(mnt_userns,...
Although, I am not sure exactly why.
Isn't mnt_userns supposed to be stable after the mount is
connected to the namespace?
What is the concern from re-quiring mnt_userns from path->mnt
inside notify_change()?
> I really want to see details on all callers - which mount are
> you going to use in each case.
The callers are:
cachefiles, ecryptfs, nfsd, devtmpfs,
do_truncate(), vfs_utimes() and file_remove_privs()
* cachefiles, ecryptfs, nfsd compose paths from stashed
mount like this all the time (e.g. for vfs_truncate(), vf_getattr()).
* devtmpfs has the parent path from and also uses it to
compose child path for vfs_getattr().
* vfs_utimes() and all callers of do_truncate() already have the
path, just need to pass it through to notify_change()
>
> The thing that is not going to be acceptable is
> a combination of mount from one filesystem and dentry from
> another. In particular, file_remove_privs() is going to be
> interesting.
>
> Note, BTW, that ftruncate() and file_remove_privs()
> are different in that respect - the latter hits d_real()
> (by way of file_dentry()), the former does not. Which one
> is correct and if both are, why are their needs different?
Nowadays (>= v4.19) I think the only files whose file_inode() and
f_path do not agree are the overlayfs "real.file" that can find their
way to f_mapping and to some vfs helpers and from there to
filesystem ops and to file_modified() or generic_file_write_iter()
and to file_remove_privs().
Contrary to that, overlayfs does not call any vfs truncate()
helper, it calls notify_change() directly (with a composed path).
So what should we do about file_remove_privs()?
Since I don't think we really need to care about generating an
event on file_remove_privs(), perhaps it could call __notify_change()
that does not generate an event and the rest of the callers call this wrapper:
int notify_change(struct path *path, struct iattr *attr,
struct inode **delegated_inode)
{
unsigned int ia_valid;
int error = __notify_change(mnt_user_ns(path->mnt), path->dentry,
attr, &ia_valid,
delegated_inode);
if (!error)
fsnotify_change(path, ia_valid);
return error;
}
Does this make sense?
Thanks,
Amir.
next prev parent reply other threads:[~2021-04-19 22:04 UTC|newest]
Thread overview: 61+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-03-28 15:56 [RFC][PATCH] fanotify: allow setting FAN_CREATE in mount mark mask Amir Goldstein
2021-03-30 7:31 ` Christian Brauner
2021-03-30 9:31 ` Amir Goldstein
2021-03-30 16:24 ` Amir Goldstein
2021-03-31 10:08 ` Christian Brauner
2021-03-31 10:57 ` Amir Goldstein
2021-04-08 11:44 ` open_by_handle_at() in userns Amir Goldstein
2021-04-08 12:55 ` Christian Brauner
2021-04-08 14:15 ` J. Bruce Fields
2021-04-08 15:54 ` Amir Goldstein
2021-04-08 16:08 ` J. Bruce Fields
2021-04-08 16:48 ` Frank Filz
2021-04-08 15:34 ` Amir Goldstein
2021-04-08 15:41 ` Christian Brauner
2021-03-30 12:12 ` [RFC][PATCH] fanotify: allow setting FAN_CREATE in mount mark mask Christian Brauner
2021-03-30 12:33 ` Amir Goldstein
2021-03-30 12:53 ` Christian Brauner
2021-03-30 12:55 ` Christian Brauner
2021-03-30 13:54 ` Amir Goldstein
2021-03-30 14:17 ` Christian Brauner
2021-03-30 14:56 ` Amir Goldstein
2021-03-31 9:46 ` Christian Brauner
2021-03-31 11:29 ` Amir Goldstein
2021-03-31 12:17 ` Christian Brauner
2021-03-31 12:59 ` Amir Goldstein
2021-03-31 12:54 ` Jan Kara
2021-03-31 14:06 ` Amir Goldstein
2021-03-31 20:59 ` fsnotify path hooks Amir Goldstein
2021-04-01 10:29 ` Jan Kara
2021-04-01 14:18 ` Amir Goldstein
2021-04-02 8:20 ` Amir Goldstein
2021-04-04 10:27 ` LSM and setxattr helpers Amir Goldstein
2021-04-05 12:23 ` Christian Brauner
2021-04-05 14:47 ` Mimi Zohar
2021-04-06 15:43 ` Amir Goldstein
2021-04-05 16:18 ` Casey Schaufler
2021-04-06 8:35 ` fsnotify path hooks Jan Kara
2021-04-06 18:49 ` Amir Goldstein
2021-04-08 12:52 ` Jan Kara
2021-04-08 15:11 ` Amir Goldstein
2021-04-09 10:08 ` Jan Kara
2021-04-09 10:45 ` Christian Brauner
2021-04-20 6:01 ` Amir Goldstein
2021-04-20 11:41 ` Christian Brauner
2021-04-20 11:58 ` Amir Goldstein
2021-04-20 13:38 ` Christian Brauner
2021-04-09 13:22 ` Amir Goldstein
2021-04-09 14:30 ` Al Viro
2021-04-09 14:39 ` Christian Brauner
2021-04-09 14:46 ` Al Viro
2021-04-09 15:20 ` Christian Brauner
2021-04-09 16:06 ` Amir Goldstein
2021-04-09 16:09 ` Amir Goldstein
2021-04-18 18:51 ` Amir Goldstein
2021-04-19 8:08 ` Amir Goldstein
2021-04-19 16:41 ` Amir Goldstein
2021-04-19 17:02 ` Al Viro
2021-04-19 22:04 ` Amir Goldstein [this message]
2021-04-20 7:53 ` Amir Goldstein
2021-03-31 13:06 ` [RFC][PATCH] fanotify: allow setting FAN_CREATE in mount mark mask J. Bruce Fields
2021-03-30 12:20 ` Amir Goldstein
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