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Date:   Thu, 31 Aug 2023 15:40:36 +0200
From:   Christian Brauner <brauner@kernel.org>
To:     Bernd Schubert <bschubert@ddn.com>
Cc:     linux-fsdevel@vger.kernel.org, bernd.schubert@fastmail.fm,
        miklos@szeredi.hu, dsingh@ddn.com,
        Josef Bacik <josef@toxicpanda.com>,
        linux-btrfs@vger.kernel.org,
        Alexander Viro <viro@zeniv.linux.org.uk>
Subject: Re: [PATCH 1/2] fs: Add and export file_needs_remove_privs
Message-ID: <20230831-letzlich-eruption-9187c3adaca6@brauner>
References: <20230831112431.2998368-1-bschubert@ddn.com>
 <20230831112431.2998368-2-bschubert@ddn.com>
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On Thu, Aug 31, 2023 at 01:24:30PM +0200, Bernd Schubert wrote:
> File systems want to hold a shared lock for DIO writes,
> but may need to drop file priveliges - that a requires an
> exclusive lock. The new export function file_needs_remove_privs()
> is added in order to first check if that is needed.
> 
> Cc: Miklos Szeredi <miklos@szeredi.hu>
> Cc: Dharmendra Singh <dsingh@ddn.com>
> Cc: Josef Bacik <josef@toxicpanda.com>
> Cc: linux-btrfs@vger.kernel.org
> Cc: Alexander Viro <viro@zeniv.linux.org.uk>
> Cc: Christian Brauner <brauner@kernel.org>
> Cc: linux-fsdevel@vger.kernel.org
> Signed-off-by: Bernd Schubert <bschubert@ddn.com>
> ---
>  fs/inode.c         | 8 ++++++++
>  include/linux/fs.h | 1 +
>  2 files changed, 9 insertions(+)
> 
> diff --git a/fs/inode.c b/fs/inode.c
> index 67611a360031..9b05db602e41 100644
> --- a/fs/inode.c
> +++ b/fs/inode.c
> @@ -2013,6 +2013,14 @@ int dentry_needs_remove_privs(struct mnt_idmap *idmap,
>  	return mask;
>  }
>  
> +int file_needs_remove_privs(struct file *file)
> +{
> +	struct dentry *dentry = file_dentry(file);
> +
> +	return dentry_needs_remove_privs(file_mnt_idmap(file), dentry);

Ugh, I wanted to propose to get rid of this dentry dance but I propsed
that before and remembered it's because of __vfs_getxattr() which is
called from the capability security hook that we need it...