linux-kernel - Re: [RFC] vfs: security: Parse dev_name before calling security_sb

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Message-ID: <5EB3EFBC-69BA-49CC-B416-D4A7398A2B47@meta.com>
Date: Thu, 10 Jul 2025 17:00:18 +0000
From: Song Liu <songliubraving@...a.com>
To: Christian Brauner <brauner@...nel.org>
CC: Paul Moore <paul@...l-moore.com>, Al Viro <viro@...iv.linux.org.uk>,
        Song
 Liu <song@...nel.org>,
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Subject: Re: [RFC] vfs: security: Parse dev_name before calling
 security_sb_mount



> On Jul 10, 2025, at 4:46 AM, Christian Brauner <brauner@...nel.org> wrote:

[...]

>> Right now, we have security_sb_mount and security_move_mount, for 
>> syscall “mount” and “move_mount” respectively. This is confusing 
>> because we can also do move mount with syscall “mount”. How about 
>> we create 5 different security hooks:
>> 
>> security_bind_mount
>> security_new_mount
>> security_reconfigure_mount
>> security_remount
>> security_change_type_mount
>> 
>> and remove security_sb_mount. After this, we will have 6 hooks for
>> each type of mount (the 5 above plus security_move_mount).
> 
> I've multiple times pointed out that the current mount security hooks
> aren't working and basically everything in the new mount api is
> unsupervised from an LSM perspective.

To make sure I understand the comment. By “new mount api”, do you mean 
the code path under do_new_mount()? 

> My recommendation is make a list of all the currently supported
> security_*() hooks in the mount code (I certainly don't have them in my
> head). Figure out what each of them allow to mediate effectively and how
> the callchains are related.
> 
> Then make a proposal how to replace them with something that a) doesn't
> cause regressions which is probably something that the LSMs care about
> and b) that covers the new mount API sufficiently to be properly
> mediated.
> 
> I'll happily review proposals. Fwiw, I'm pretty sure that this is
> something that Mickael is interested in as well.

So we will consider a proper redesign of LSM hooks for mount syscalls, 
but we do not want incremental improvements like this one. Do I get 
the direction right?

Thanks,
Song