From: David Howells <dhowells@redhat.com>
To: Jann Horn <jannh@google.com>
Cc: dhowells@redhat.com, Al Viro <viro@zeniv.linux.org.uk>,
raven@themaw.net, linux-fsdevel <linux-fsdevel@vger.kernel.org>,
Linux API <linux-api@vger.kernel.org>,
linux-block@vger.kernel.org, keyrings@vger.kernel.org,
linux-security-module <linux-security-module@vger.kernel.org>,
kernel list <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH 4/7] vfs: Add superblock notifications
Date: Wed, 29 May 2019 13:58:39 +0100 [thread overview]
Message-ID: <24577.1559134719@warthog.procyon.org.uk> (raw)
In-Reply-To: <CAG48ez2o1egR13FDd3=CgdXP_MbBsZM4SX=+aqvR6eheWddhFg@mail.gmail.com>
Jann Horn <jannh@google.com> wrote:
> It might make sense to require that the path points to the root inode
> of the superblock? That way you wouldn't be able to do this on a bind
> mount that exposes part of a shared filesystem to a container.
Why prevent that? It doesn't prevent the container denizen from watching a
bind mount that exposes the root of a shared filesystem into a container.
It probably makes sense to permit the LSM to rule on whether a watch may be
emplaced, however.
> > + ret = add_watch_to_object(watch, s->s_watchers);
> > + if (ret == 0) {
> > + spin_lock(&sb_lock);
> > + s->s_count++;
> > + spin_unlock(&sb_lock);
>
> Why do watches hold references on the superblock they're watching?
Fair point. It was necessary at one point, but I don't think it is now. I'll
see if I can remove it. Note that it doesn't stop a superblock from being
unmounted and destroyed.
> > + }
> > + }
> > + up_write(&s->s_umount);
> > + if (ret < 0)
> > + kfree(watch);
> > + } else if (s->s_watchers) {
>
> This should probably have something like a READ_ONCE() for clarity?
Note that I think I'll rearrange this to:
} else {
ret = -EBADSLT;
if (s->s_watchers) {
down_write(&s->s_umount);
ret = remove_watch_from_object(s->s_watchers, wqueue,
s->s_unique_id, false);
up_write(&s->s_umount);
}
}
I'm not sure READ_ONCE() is necessary, since s_watchers can only be
instantiated once and the watch list then persists until the superblock is
deactivated. Furthermore, by the time deactivate_locked_super() is called, we
can't be calling sb_notify() on it as it's become inaccessible.
So if we see s->s_watchers as non-NULL, we should not see anything different
inside the lock. In fact, I should be able to rewrite the above to:
} else {
ret = -EBADSLT;
wlist = s->s_watchers;
if (wlist) {
down_write(&s->s_umount);
ret = remove_watch_from_object(wlist, wqueue,
s->s_unique_id, false);
up_write(&s->s_umount);
}
}
David
next prev parent reply other threads:[~2019-05-29 12:58 UTC|newest]
Thread overview: 65+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-05-28 16:01 [RFC][PATCH 0/7] Mount, FS, Block and Keyrings notifications David Howells
2019-05-28 16:01 ` [PATCH 1/7] General notification queue with user mmap()'able ring buffer David Howells
2019-05-28 16:26 ` Greg KH
2019-05-28 17:30 ` David Howells
2019-05-28 23:12 ` Greg KH
2019-05-29 16:06 ` David Howells
2019-05-29 17:46 ` Jann Horn
2019-05-29 21:02 ` David Howells
2019-05-31 11:14 ` Peter Zijlstra
2019-05-31 12:02 ` David Howells
2019-05-31 13:26 ` Peter Zijlstra
2019-05-31 14:20 ` David Howells
2019-05-31 16:44 ` Peter Zijlstra
2019-05-31 17:12 ` David Howells
2019-06-17 16:24 ` Peter Zijlstra
2019-05-29 23:09 ` Greg KH
2019-05-29 23:11 ` Greg KH
2019-05-30 9:50 ` Andrea Parri
2019-05-31 8:35 ` Peter Zijlstra
2019-05-31 8:47 ` Peter Zijlstra
2019-05-31 12:42 ` David Howells
2019-05-31 14:55 ` David Howells
2019-05-28 19:14 ` Jann Horn
2019-05-28 22:28 ` David Howells
2019-05-28 23:16 ` Jann Horn
2019-05-28 16:02 ` [PATCH 2/7] keys: Add a notification facility David Howells
2019-05-28 16:02 ` [PATCH 3/7] vfs: Add a mount-notification facility David Howells
2019-05-28 20:06 ` Jann Horn
2019-05-28 23:04 ` David Howells
2019-05-28 23:23 ` Jann Horn
2019-05-29 11:16 ` David Howells
2019-05-28 23:08 ` David Howells
2019-05-29 10:55 ` David Howells
2019-05-29 11:00 ` David Howells
2019-05-29 15:53 ` Casey Schaufler
2019-05-29 16:12 ` Jann Horn
2019-05-29 17:04 ` Casey Schaufler
2019-06-03 16:30 ` David Howells
2019-05-29 17:13 ` Andy Lutomirski
2019-05-29 17:46 ` Casey Schaufler
2019-05-29 18:11 ` Jann Horn
2019-05-29 19:28 ` Casey Schaufler
2019-05-29 19:47 ` Jann Horn
2019-05-29 20:50 ` Casey Schaufler
2019-05-29 23:12 ` Andy Lutomirski
2019-05-29 23:56 ` Casey Schaufler
2019-05-28 16:02 ` [PATCH 4/7] vfs: Add superblock notifications David Howells
2019-05-28 20:27 ` Jann Horn
2019-05-29 12:58 ` David Howells [this message]
2019-05-29 14:16 ` Jann Horn
2019-05-28 16:02 ` [PATCH 5/7] fsinfo: Export superblock notification counter David Howells
2019-05-28 16:02 ` [PATCH 6/7] block: Add block layer notifications David Howells
2019-05-28 20:37 ` Jann Horn
2019-05-28 16:02 ` [PATCH 7/7] Add sample notification program David Howells
2019-05-28 23:58 ` [RFC][PATCH 0/7] Mount, FS, Block and Keyrings notifications Greg KH
2019-05-29 6:33 ` Amir Goldstein
2019-05-29 14:25 ` Jan Kara
2019-05-29 15:10 ` Greg KH
2019-05-29 15:53 ` Amir Goldstein
2019-05-30 11:00 ` Jan Kara
2019-06-04 12:33 ` David Howells
2019-05-29 6:45 ` David Howells
2019-05-29 7:40 ` Amir Goldstein
2019-05-29 9:09 ` David Howells
2019-05-29 15:41 ` Casey Schaufler
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