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Date:   Fri, 15 Apr 2022 16:09:24 +0200
From:   Christian Brauner <brauner@kernel.org>
To:     Yang Xu <xuyang2018.jy@fujitsu.com>
Cc:     david@fromorbit.com, djwong@kernel.org,
        linux-fsdevel@vger.kernel.org, ceph-devel@vger.kernel.org,
        linux-nfs@vger.kernel.org, linux-xfs@vger.kernel.org,
        viro@zeniv.linux.org.uk, jlayton@kernel.org
Subject: Re: [PATCH v3 1/7] fs/inode: move sgid strip operation from
 inode_init_owner into inode_sgid_strip
Message-ID: <20220415140924.oirar6dklelujnxs@wittgenstein>
References: <1650020543-24908-1-git-send-email-xuyang2018.jy@fujitsu.com>
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In-Reply-To: <1650020543-24908-1-git-send-email-xuyang2018.jy@fujitsu.com>
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On Fri, Apr 15, 2022 at 07:02:17PM +0800, Yang Xu wrote:
> This has no functional change. Just create and export inode_sgid_strip api for
> the subsequent patch. This function is used to strip S_ISGID mode when init
> a new inode.
> 
> Signed-off-by: Yang Xu <xuyang2018.jy@fujitsu.com>
> ---
> v2->v3:
> 1.Use const struct inode * instead of struct inode *
> 2.replace sgid strip with inode_sgid_strip in a single patch
>  fs/inode.c         | 24 ++++++++++++++++++++----
>  include/linux/fs.h |  3 ++-
>  2 files changed, 22 insertions(+), 5 deletions(-)
> 
> diff --git a/fs/inode.c b/fs/inode.c
> index 9d9b422504d1..1b569ad882ce 100644
> --- a/fs/inode.c
> +++ b/fs/inode.c
> @@ -2246,10 +2246,8 @@ void inode_init_owner(struct user_namespace *mnt_userns, struct inode *inode,
>  		/* Directories are special, and always inherit S_ISGID */
>  		if (S_ISDIR(mode))
>  			mode |= S_ISGID;
> -		else if ((mode & (S_ISGID | S_IXGRP)) == (S_ISGID | S_IXGRP) &&
> -			 !in_group_p(i_gid_into_mnt(mnt_userns, dir)) &&
> -			 !capable_wrt_inode_uidgid(mnt_userns, dir, CAP_FSETID))
> -			mode &= ~S_ISGID;
> +		else
> +			inode_sgid_strip(mnt_userns, dir, &mode);
>  	} else
>  		inode_fsgid_set(inode, mnt_userns);
>  	inode->i_mode = mode;
> @@ -2405,3 +2403,21 @@ struct timespec64 current_time(struct inode *inode)
>  	return timestamp_truncate(now, inode);
>  }
>  EXPORT_SYMBOL(current_time);
> +
> +void inode_sgid_strip(struct user_namespace *mnt_userns,
> +		      const struct inode *dir, umode_t *mode)
> +{
> +	if (!dir || !(dir->i_mode & S_ISGID))
> +		return;
> +	if ((*mode & (S_ISGID | S_IXGRP)) != (S_ISGID | S_IXGRP))
> +		return;
> +	if (S_ISDIR(*mode))
> +		return;

I'd place that check first as this whole function is really only
relevant for non-directories.

Otherwise I can live with *mode being a pointer although I still find
this unpleasant API wise but the bikeshed does it's job without having
my color. :)

I'd like to do some good testing on this.

Acked-by: Christian Brauner (Microsoft) <brauner@kernel.org>