linux-kernel - Re: [PATCH] cachefiles: Allow the cache to be non-root

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Date:   Fri, 19 May 2023 13:26:56 -0400
From:   Jeff Layton <jlayton@...nel.org>
To:     David Howells <dhowells@...hat.com>, linux-cachefs@...hat.com
Cc:     linux-erofs@...ts.ozlabs.org, linux-fsdevel@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] cachefiles: Allow the cache to be non-root

On Fri, 2023-05-19 at 18:21 +0100, David Howells wrote:
>     
> Set mode 0600 on files in the cache so that cachefilesd can run as an
> unprivileged user rather than leaving the files all with 0.  Directories
> are already set to 0700.
> 
> Userspace then needs to set the uid and gid before issuing the "bind"
> command and the cache must've been chown'd to those IDs.
> 
> Signed-off-by: David Howells <dhowells@...hat.com>
> cc: David Howells <dhowells@...hat.com>
> cc: Jeff Layton <jlayton@...nel.org>
> cc: linux-cachefs@...hat.com
> cc: linux-erofs@...ts.ozlabs.org
> cc: linux-fsdevel@...r.kernel.org
> ---
>  fs/cachefiles/namei.c |    3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/fs/cachefiles/namei.c b/fs/cachefiles/namei.c
> index 82219a8f6084..66482c193e86 100644
> --- a/fs/cachefiles/namei.c
> +++ b/fs/cachefiles/namei.c
> @@ -451,7 +451,8 @@ struct file *cachefiles_create_tmpfile(struct cachefiles_object *object)
>  
>  	ret = cachefiles_inject_write_error();
>  	if (ret == 0) {
> -		file = vfs_tmpfile_open(&nop_mnt_idmap, &parentpath, S_IFREG,
> +		file = vfs_tmpfile_open(&nop_mnt_idmap, &parentpath,
> +					S_IFREG | 0600,
>  					O_RDWR | O_LARGEFILE | O_DIRECT,
>  					cache->cache_cred);
>  		ret = PTR_ERR_OR_ZERO(file);
> 

Seems safe enough, and if it helps allow this to run unprivileged then:

Reviewed-by: Jeff Layton <jlayton@...nel.org>