Re: [PATCH] ovl: Do not override fsuid and fsgid in ovl_link()

From: Amir Goldstein <amir73il@gmail.com>
To: Zhang Tianci <zhangtianci.1997@bytedance.com>
Cc: Miklos Szeredi <miklos@szeredi.hu>,
	overlayfs <linux-unionfs@vger.kernel.org>,
	linux-kernel <linux-kernel@vger.kernel.org>,
	Jiachen Zhang <zhangjiachen.jaycee@bytedance.com>
Subject: Re: [PATCH] ovl: Do not override fsuid and fsgid in ovl_link()
Date: Wed, 17 Aug 2022 10:36:38 +0300	[thread overview]
Message-ID: <CAOQ4uxgrkPYBkZG--70s4PnUiT0ht=GdWrrm+aY4ZHoZjZrWAw@mail.gmail.com> (raw)
In-Reply-To: <20220817034559.44936-1-zhangtianci.1997@bytedance.com>

On Wed, Aug 17, 2022 at 6:49 AM Zhang Tianci
<zhangtianci.1997@bytedance.com> wrote:
>
> ovl_link() did not create a new inode after commit
> 51f7e52dc943 ("ovl: share inode for hard link"), so
> in ovl_create_or_link() we should not override cred's
> fsuid and fsgid when called by ovl_link().
>
> Signed-off-by: Zhang Tianci <zhangtianci.1997@bytedance.com>
> Signed-off-by: Jiachen Zhang <zhangjiachen.jaycee@bytedance.com>
> ---
>  fs/overlayfs/dir.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/fs/overlayfs/dir.c b/fs/overlayfs/dir.c
> index 6b03457f72bb..568d338032db 100644
> --- a/fs/overlayfs/dir.c
> +++ b/fs/overlayfs/dir.c
> @@ -595,9 +595,9 @@ static int ovl_create_or_link(struct dentry *dentry, struct inode *inode,
>         err = -ENOMEM;
>         override_cred = prepare_creds();
>         if (override_cred) {
> -               override_cred->fsuid = inode->i_uid;
> -               override_cred->fsgid = inode->i_gid;
>                 if (!attr->hardlink) {
> +                       override_cred->fsuid = inode->i_uid;
> +                       override_cred->fsgid = inode->i_gid;
>                         err = security_dentry_create_files_as(dentry,
>                                         attr->mode, &dentry->d_name, old_cred,
>                                         override_cred);
> --

This change looks incorrect.
Unless I am missing something, fsuid/fsgid still need to
be overridden for calling link() on underlying fs.
What made you do this change?

Thanks,
Amir.