linux-kernel - Re: [PATCH] fsnotify: add generic perm check for unlink/rmdir

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Date:   Tue, 17 May 2022 21:17:06 -0400
From:   Paul Moore <paul@...l-moore.com>
To:     Guowei Du <duguoweisz@...il.com>
Cc:     jack@...e.cz, amir73il@...il.com, linux-fsdevel@...r.kernel.org,
        linux-kernel@...r.kernel.org, viro@...iv.linux.org.uk,
        jmorris@...ei.org, serge@...lyn.com, ast@...nel.org,
        daniel@...earbox.net, andrii@...nel.org, kafai@...com,
        songliubraving@...com, yhs@...com, john.fastabend@...il.com,
        kpsingh@...nel.org, linux-security-module@...r.kernel.org,
        netdev@...r.kernel.org, bpf@...r.kernel.org,
        stephen.smalley.work@...il.com, eparis@...isplace.org,
        keescook@...omium.org, anton@...msg.org, ccross@...roid.com,
        tony.luck@...el.com, selinux@...r.kernel.org,
        duguowei <duguowei@...omi.com>
Subject: Re: [PATCH] fsnotify: add generic perm check for unlink/rmdir

On Tue, May 3, 2022 at 2:38 PM Guowei Du <duguoweisz@...il.com> wrote:
>
> From: duguowei <duguowei@...omi.com>
>
> For now, there have been open/access/open_exec perms for file operation,
> so we add new perms check with unlink/rmdir syscall. if one app deletes
> any file/dir within pubic area, fsnotify can sends fsnotify_event to
> listener to deny that, even if the app have right dac/mac permissions.
>
> Signed-off-by: duguowei <duguowei@...omi.com>
> ---
>  fs/notify/fsnotify.c             |  2 +-
>  include/linux/fs.h               |  2 ++
>  include/linux/fsnotify.h         | 16 ++++++++++++++++
>  include/linux/fsnotify_backend.h |  6 +++++-
>  security/security.c              | 12 ++++++++++--
>  security/selinux/hooks.c         |  4 ++++
>  6 files changed, 38 insertions(+), 4 deletions(-)

...

> diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
> index e9e959343de9..f0780f0eb903 100644
> --- a/security/selinux/hooks.c
> +++ b/security/selinux/hooks.c
> @@ -1801,8 +1801,12 @@ static int may_create(struct inode *dir,
>  }
>
>  #define MAY_LINK       0
> +#ifndef MAY_UNLINK
>  #define MAY_UNLINK     1
> +#endif
> +#ifndef MAY_RMDIR
>  #define MAY_RMDIR      2
> +#endif

In the future if you run into a symbol collision here I would prefer
if you renamed the SELinux constants to something like SEL_MAY_LINK,
etc.

-- 
paul-moore.com