linux-kernel - Re: [PATCH v2] fsnotify, lsm: Decouple fsnotify from lsm

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Message-ID: <AE7ECD50-A7DC-4D7D-8BC7-2A555A327483@fb.com>
Date: Sun, 13 Oct 2024 14:45:54 +0000
From: Song Liu <songliubraving@...a.com>
To: Amir Goldstein <amir73il@...il.com>
CC: Song Liu <song@...nel.org>, Linux-Fsdevel <linux-fsdevel@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        LSM List
	<linux-security-module@...r.kernel.org>,
        Al Viro <viro@...iv.linux.org.uk>,
        Christian Brauner <brauner@...nel.org>, Jan Kara <jack@...e.cz>,
        Paul Moore
	<paul@...l-moore.com>, James Morris <jmorris@...ei.org>,
        "Serge E. Hallyn"
	<serge@...lyn.com>,
        Kernel Team <kernel-team@...a.com>
Subject: Re: [PATCH v2] fsnotify, lsm: Decouple fsnotify from lsm

Hi Amir, 

> On Oct 13, 2024, at 2:38 AM, Amir Goldstein <amir73il@...il.com> wrote:
> 
> On Sun, Oct 13, 2024 at 2:23 AM Song Liu <song@...nel.org> wrote:
>> 
>> Currently, fsnotify_open_perm() is called from security_file_open(). This
>> is not right for CONFIG_SECURITY=n and CONFIG_FSNOTIFY=y case, as
>> security_file_open() in this combination will be a no-op and not call
>> fsnotify_open_perm(). Fix this by calling fsnotify_open_perm() directly.
> 
> Maybe I am missing something.
> I like cleaner interfaces, but if it is a report of a problem then
> I do not understand what the problem is.
> IOW, what does "This is not right" mean?

With existing code, CONFIG_FANOTIFY_ACCESS_PERMISSIONS depends on 
CONFIG_SECURITY, but CONFIG_FSNOTIFY does not depend on 
CONFIG_SECURITY. So CONFIG_SECURITY=n and CONFIG_FSNOTIFY=y is a
valid combination. fsnotify_open_perm() is an fsnotify API, so I
think it is not right to skip the API call for this config.

> 
>> 
>> After this, CONFIG_FANOTIFY_ACCESS_PERMISSIONS does not require
>> CONFIG_SECURITY any more. Remove the dependency in the config.
>> 
>> Signed-off-by: Song Liu <song@...nel.org>
>> Acked-by: Paul Moore <paul@...l-moore.com>
>> 
>> ---
>> 
>> v1: https://lore.kernel.org/linux-fsdevel/20241011203722.3749850-1-song@kernel.org/
>> 
>> As far as I can tell, it is necessary to back port this to stable. Because
>> CONFIG_FANOTIFY_ACCESS_PERMISSIONS is the only user of fsnotify_open_perm,
>> and CONFIG_FANOTIFY_ACCESS_PERMISSIONS depends on CONFIG_SECURITY.
>> Therefore, the following tags are not necessary. But I include here as
>> these are discussed in v1.
> 
> I did not understand why you claim that the tags are or not necessary.
> The dependency is due to removal of the fsnotify.h include.

I think the Fixes tag is also not necessary, not just the two 
Depends-on tags. This is because while fsnotify_open_perm() is a 
fsnotify API, only CONFIG_FANOTIFY_ACCESS_PERMISSIONS really uses 
(if I understand correctly). 

> 
> Anyway, I don't think it is critical to backport this fix.
> The dependencies would probably fail to apply cleanly to older kernels,
> so unless somebody cares, it would stay this way.

I agree it is not critical to back port this fix. I put the 
Fixes tag below "---" for this reason. 

Does this answer your question? 

Thanks,
Song

> 
>> 
>> Fixes: c4ec54b40d33 ("fsnotify: new fsnotify hooks and events types for access decisions")
> 
> Because I am not sure what the problem is, I am not sure that a Fixes:
> tag is called for.
> 
>> Depends-on: 36e28c42187c ("fsnotify: split fsnotify_perm() into two hooks")
>> Depends-on: d9e5d31084b0 ("fsnotify: optionally pass access range in file permission hooks")
> 
> These need to be in the commit message in case AUTOSEL or a developer
> would decide to backport your change.
> 
> Thanks,
> Amir.