[PATCH] fsnotify, lsm: Separate fsnotify_open_perm() and security_file_open()

[Song Liu]

Hi Amir, 

Thanks for the review. 

> On Oct 12, 2024, at 12:09 AM, Amir Goldstein <amir73il at gmail.com> wrote:
> 
> On Fri, Oct 11, 2024 at 11:42 PM Paul Moore <paul at paul-moore.com> wrote:
>> 
>> On Oct 11, 2024 Song Liu <song at kernel.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.
>>> 
>>> Signed-off-by: Song Liu <song at kernel.org>
>>> ---
>>> PS: I didn't included a Fixes tag. This issue was probably introduced 15
>>> years ago in [1]. If we want to back port this to stable, we will need
>>> another version for older kernel because of [2].
>>> 
>>> [1] c4ec54b40d33 ("fsnotify: new fsnotify hooks and events types for access decisions")
>>> [2] 36e28c42187c ("fsnotify: split fsnotify_perm() into two hooks")
>>> ---
>>> fs/open.c           | 4 ++++
>>> security/security.c | 9 +--------
>>> 2 files changed, 5 insertions(+), 8 deletions(-)
> 
> Nice cleanup, but please finish off the coupling of lsm/fsnotify altogether.
> I would either change the title to "decouple fsnotify from lsm" or
> submit an additional patch with that title.
> 
> diff --git a/fs/notify/fanotify/Kconfig b/fs/notify/fanotify/Kconfig
> index a511f9d8677b..0e36aaf379b7 100644
> --- a/fs/notify/fanotify/Kconfig
> +++ b/fs/notify/fanotify/Kconfig
> @@ -15,7 +15,6 @@ config FANOTIFY
> config FANOTIFY_ACCESS_PERMISSIONS
>        bool "fanotify permissions checking"
>        depends on FANOTIFY
> -       depends on SECURITY
>        default n
>        help
>           Say Y here is you want fanotify listeners to be able to
> make permissions

I will send v2 with this change. 

> diff --git a/security/security.c b/security/security.c
> index 6875eb4a59fc..8d238ffdeb4a 100644
> --- a/security/security.c
> +++ b/security/security.c
> @@ -19,7 +19,6 @@
> #include <linux/kernel.h>
> #include <linux/kernel_read_file.h>
> #include <linux/lsm_hooks.h>
> -#include <linux/fsnotify.h>
> #include <linux/mman.h>
> #include <linux/mount.h>
> #include <linux/personality.h>
> 
>> 
>> This looks fine to me, if we can get an ACK from the VFS folks I can
>> merge this into the lsm/stable-6.12 tree and send it to Linus, or the
>> VFS folks can do it if they prefer (my ACK is below just in case).
> 
> My preference would be to take this via the vfs or fsnotify tree.
> 
>> 
>> As far as stable prior to v6.8 is concerned, once this hits Linus'
>> tree you can submit an adjusted backport for the older kernels to the
>> stable team.
> 
> Please do NOT submit an adjustable backport.
> Instead please include the following tags for the decoupling patch:
> 
> Depends-on: 36e28c42187c fsnotify: split fsnotify_perm() into two hooks
> Depends-on: d9e5d31084b0 fsnotify: optionally pass access range in
> file permission hooks

IIUC, FANOTIFY_ACCESS_PERMISSIONS is the only user of FS_OPEN_EXEC_PERM
and FS_OPEN_PERM. In this case, I think we don't need to back port this
to stable, because there is no user of fsnotify_open_perm without 
CONFIG_SECURITY. Did I miss something?

Thanks,
Song