From: Casey Schaufler <casey@schaufler-ca.com>
To: David Howells <dhowells@redhat.com>, Jann Horn <jannh@google.com>
Cc: 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 3/7] vfs: Add a mount-notification facility
Date: Wed, 29 May 2019 08:53:34 -0700 [thread overview]
Message-ID: <312a138c-e5b2-4bfb-b50b-40c82c55773f@schaufler-ca.com> (raw)
In-Reply-To: <14347.1559127657@warthog.procyon.org.uk>
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On 5/29/2019 4:00 AM, David Howells wrote:
> Jann Horn <jannh@google.com> wrote:
>
>>> +void post_mount_notification(struct mount *changed,
>>> + struct mount_notification *notify)
>>> +{
>>> + const struct cred *cred = current_cred();
>> This current_cred() looks bogus to me. Can't mount topology changes
>> come from all sorts of places? For example, umount_mnt() from
>> umount_tree() from dissolve_on_fput() from __fput(), which could
>> happen pretty much anywhere depending on where the last reference gets
>> dropped?
> IIRC, that's what Casey argued is the right thing to do from a security PoV.
> Casey?
You need to identify the credential of the subject that triggered
the event. If it isn't current_cred(), the cred needs to be passed
in to post_mount_notification(), or derived by some other means.
> Maybe I should pass in NULL creds in the case that an event is being generated
> because an object is being destroyed due to the last usage[*] being removed.
You should pass the cred of the process that removed the
last usage. If the last usage was removed by something like
the power being turned off on a disk drive a system cred
should be used. Someone or something caused the event. It can
be important who it was.
> [*] Usage, not ref - Superblocks are a bit weird in their accounting.
>
> David
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WARNING: multiple messages have this Message-ID (diff)
From: Casey Schaufler <casey@schaufler-ca.com>
To: David Howells <dhowells@redhat.com>, Jann Horn <jannh@google.com>
Cc: 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 3/7] vfs: Add a mount-notification facility
Date: Wed, 29 May 2019 15:53:34 +0000 [thread overview]
Message-ID: <312a138c-e5b2-4bfb-b50b-40c82c55773f@schaufler-ca.com> (raw)
In-Reply-To: <14347.1559127657@warthog.procyon.org.uk>
[-- Attachment #1.1: Type: text/plain, Size: 1386 bytes --]
On 5/29/2019 4:00 AM, David Howells wrote:
> Jann Horn <jannh@google.com> wrote:
>
>>> +void post_mount_notification(struct mount *changed,
>>> + struct mount_notification *notify)
>>> +{
>>> + const struct cred *cred = current_cred();
>> This current_cred() looks bogus to me. Can't mount topology changes
>> come from all sorts of places? For example, umount_mnt() from
>> umount_tree() from dissolve_on_fput() from __fput(), which could
>> happen pretty much anywhere depending on where the last reference gets
>> dropped?
> IIRC, that's what Casey argued is the right thing to do from a security PoV.
> Casey?
You need to identify the credential of the subject that triggered
the event. If it isn't current_cred(), the cred needs to be passed
in to post_mount_notification(), or derived by some other means.
> Maybe I should pass in NULL creds in the case that an event is being generated
> because an object is being destroyed due to the last usage[*] being removed.
You should pass the cred of the process that removed the
last usage. If the last usage was removed by something like
the power being turned off on a disk drive a system cred
should be used. Someone or something caused the event. It can
be important who it was.
> [*] Usage, not ref - Superblocks are a bit weird in their accounting.
>
> David
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next prev parent reply other threads:[~2019-05-29 15:53 UTC|newest]
Thread overview: 131+ 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 ` David Howells
2019-05-28 16:01 ` [PATCH 1/7] General notification queue with user mmap()'able ring buffer David Howells
2019-05-28 16:01 ` David Howells
2019-05-28 16:26 ` Greg KH
2019-05-28 16:26 ` Greg KH
2019-05-28 17:30 ` David Howells
2019-05-28 17:30 ` David Howells
2019-05-28 23:12 ` Greg KH
2019-05-28 23:12 ` Greg KH
2019-05-29 16:06 ` David Howells
2019-05-29 16:06 ` David Howells
2019-05-29 17:46 ` Jann Horn
2019-05-29 17:46 ` Jann Horn
2019-05-29 21:02 ` David Howells
2019-05-29 21:02 ` David Howells
2019-05-31 11:14 ` Peter Zijlstra
2019-05-31 11:14 ` Peter Zijlstra
2019-05-31 12:02 ` David Howells
2019-05-31 12:02 ` David Howells
2019-05-31 13:26 ` Peter Zijlstra
2019-05-31 13:26 ` Peter Zijlstra
2019-05-31 14:20 ` David Howells
2019-05-31 14:20 ` David Howells
2019-05-31 16:44 ` Peter Zijlstra
2019-05-31 16:44 ` Peter Zijlstra
2019-05-31 17:12 ` David Howells
2019-05-31 17:12 ` David Howells
2019-06-17 16:24 ` Peter Zijlstra
2019-06-17 16:24 ` Peter Zijlstra
2019-05-29 23:09 ` Greg KH
2019-05-29 23:09 ` Greg KH
2019-05-29 23:11 ` Greg KH
2019-05-29 23:11 ` Greg KH
2019-05-30 9:50 ` Andrea Parri
2019-05-30 9:50 ` Andrea Parri
2019-05-31 8:35 ` Peter Zijlstra
2019-05-31 8:35 ` Peter Zijlstra
2019-05-31 8:47 ` Peter Zijlstra
2019-05-31 8:47 ` Peter Zijlstra
2019-05-31 12:42 ` David Howells
2019-05-31 12:42 ` David Howells
2019-05-31 14:55 ` David Howells
2019-05-31 14:55 ` David Howells
2019-05-28 19:14 ` Jann Horn
2019-05-28 19:14 ` Jann Horn
2019-05-28 22:28 ` David Howells
2019-05-28 22:28 ` David Howells
2019-05-28 23:16 ` Jann Horn
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 ` David Howells
2019-05-28 16:02 ` [PATCH 3/7] vfs: Add a mount-notification facility David Howells
2019-05-28 16:02 ` David Howells
2019-05-28 20:06 ` Jann Horn
2019-05-28 20:06 ` Jann Horn
2019-05-28 23:04 ` David Howells
2019-05-28 23:04 ` David Howells
2019-05-28 23:23 ` Jann Horn
2019-05-28 23:23 ` Jann Horn
2019-05-29 11:16 ` David Howells
2019-05-29 11:16 ` David Howells
2019-05-28 23:08 ` David Howells
2019-05-28 23:08 ` David Howells
2019-05-29 10:55 ` David Howells
2019-05-29 10:55 ` David Howells
2019-05-29 11:00 ` David Howells
2019-05-29 11:00 ` David Howells
2019-05-29 15:53 ` Casey Schaufler [this message]
2019-05-29 15:53 ` Casey Schaufler
2019-05-29 16:12 ` Jann Horn
2019-05-29 16:12 ` Jann Horn
2019-05-29 17:04 ` Casey Schaufler
2019-05-29 17:04 ` Casey Schaufler
2019-06-03 16:30 ` David Howells
2019-06-03 16:30 ` David Howells
2019-05-29 17:13 ` Andy Lutomirski
2019-05-29 17:13 ` Andy Lutomirski
2019-05-29 17:46 ` Casey Schaufler
2019-05-29 17:46 ` Casey Schaufler
2019-05-29 18:11 ` Jann Horn
2019-05-29 18:11 ` Jann Horn
2019-05-29 19:28 ` Casey Schaufler
2019-05-29 19:28 ` Casey Schaufler
2019-05-29 19:47 ` Jann Horn
2019-05-29 19:47 ` Jann Horn
2019-05-29 20:50 ` Casey Schaufler
2019-05-29 20:50 ` Casey Schaufler
2019-05-29 23:12 ` Andy Lutomirski
2019-05-29 23:12 ` Andy Lutomirski
2019-05-29 23:56 ` Casey Schaufler
2019-05-29 23:56 ` Casey Schaufler
2019-05-28 16:02 ` [PATCH 4/7] vfs: Add superblock notifications David Howells
2019-05-28 16:02 ` David Howells
2019-05-28 20:27 ` Jann Horn
2019-05-28 20:27 ` Jann Horn
2019-05-29 12:58 ` David Howells
2019-05-29 12:58 ` David Howells
2019-05-29 14:16 ` Jann Horn
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 ` David Howells
2019-05-28 16:02 ` [PATCH 6/7] block: Add block layer notifications David Howells
2019-05-28 16:02 ` David Howells
2019-05-28 20:37 ` Jann Horn
2019-05-28 20:37 ` Jann Horn
2019-05-28 16:02 ` [PATCH 7/7] Add sample notification program David Howells
2019-05-28 16:02 ` David Howells
2019-05-28 23:58 ` [RFC][PATCH 0/7] Mount, FS, Block and Keyrings notifications Greg KH
2019-05-28 23:58 ` Greg KH
2019-05-29 6:33 ` Amir Goldstein
2019-05-29 6:33 ` Amir Goldstein
2019-05-29 6:33 ` Amir Goldstein
2019-05-29 14:25 ` Jan Kara
2019-05-29 14:25 ` Jan Kara
2019-05-29 15:10 ` Greg KH
2019-05-29 15:10 ` Greg KH
2019-05-29 15:53 ` Amir Goldstein
2019-05-29 15:53 ` Amir Goldstein
2019-05-30 11:00 ` Jan Kara
2019-05-30 11:00 ` Jan Kara
2019-06-04 12:33 ` David Howells
2019-06-04 12:33 ` David Howells
2019-05-29 6:45 ` David Howells
2019-05-29 6:45 ` David Howells
2019-05-29 7:40 ` Amir Goldstein
2019-05-29 7:40 ` Amir Goldstein
2019-05-29 9:09 ` David Howells
2019-05-29 9:09 ` David Howells
2019-05-29 15:41 ` Casey Schaufler
2019-05-29 15:41 ` Casey Schaufler
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