linux-ext4 - Re: [PATCH 01/14] fs_parse: add uid & gid option option parsing helpers

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Message-ID: <20240628094517.ifs4bp73nlggsnxz@quack3>
Date: Fri, 28 Jun 2024 11:45:17 +0200
From: Jan Kara <jack@...e.cz>
To: Eric Sandeen <sandeen@...hat.com>
Cc: linux-fsdevel@...r.kernel.org, Christian Brauner <brauner@...nel.org>,
	autofs@...r.kernel.org, "Rafael J. Wysocki" <rafael@...nel.org>,
	linux-efi@...r.kernel.org, Namjae Jeon <linkinjeon@...nel.org>,
	linux-ext4@...r.kernel.org, Miklos Szeredi <miklos@...redi.hu>,
	linux-mm@...ck.org, Jan Kara <jack@...e.cz>, ntfs3@...ts.linux.dev,
	linux-cifs@...r.kernel.org, linux-trace-kernel@...r.kernel.org,
	Hans Caniullan <hcaniull@...hat.com>
Subject: Re: [PATCH 01/14] fs_parse: add uid & gid option option parsing
 helpers

On Thu 27-06-24 19:26:24, Eric Sandeen wrote:
> Multiple filesystems take uid and gid as options, and the code to
> create the ID from an integer and validate it is standard boilerplate
> that can be moved into common helper functions, so do that for
> consistency and less cut&paste.
> 
> This also helps avoid the buggy pattern noted by Seth Jenkins at
> https://lore.kernel.org/lkml/CALxfFW4BXhEwxR0Q5LSkg-8Vb4r2MONKCcUCVioehXQKr35eHg@mail.gmail.com/
> because uid/gid parsing will fail before any assignment in most
> filesystems.
> 
> Signed-off-by: Eric Sandeen <sandeen@...deen.net>

I like the idea since this seems like a nobrainer but is actually
surprisingly subtle...

> diff --git a/fs/fs_parser.c b/fs/fs_parser.c
> index a4d6ca0b8971..24727ec34e5a 100644
> --- a/fs/fs_parser.c
> +++ b/fs/fs_parser.c
> @@ -308,6 +308,40 @@ int fs_param_is_fd(struct p_log *log, const struct fs_parameter_spec *p,
>  }
>  EXPORT_SYMBOL(fs_param_is_fd);
>  
> +int fs_param_is_uid(struct p_log *log, const struct fs_parameter_spec *p,
> +		    struct fs_parameter *param, struct fs_parse_result *result)
> +{
> +	kuid_t uid;
> +
> +	if (fs_param_is_u32(log, p, param, result) != 0)
> +		return fs_param_bad_value(log, param);
> +
> +	uid = make_kuid(current_user_ns(), result->uint_32);

But here is the problem: Filesystems mountable in user namespaces need to use
fc->user_ns for resolving uids / gids (e.g. like fuse_parse_param()).
Having helpers that work for some filesystems and are subtly broken for
others is worse than no helpers... Or am I missing something?

And the problem with fc->user_ns is that currently __fs_parse() does not
get fs_context as an argument... So that will need some larger work.

								Honza
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR