netdev - RE: [PATCH bpf-next 1/8] bpf: fail BPF_TOKEN_CREATE if no delegation option was set on BPF FS

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Message-ID: <6577802ea99b2_edaa208b7@john.notmuch>
Date: Mon, 11 Dec 2023 13:33:34 -0800
From: John Fastabend <john.fastabend@...il.com>
To: Andrii Nakryiko <andrii@...nel.org>, 
 bpf@...r.kernel.org, 
 netdev@...r.kernel.org, 
 paul@...l-moore.com, 
 brauner@...nel.org
Cc: linux-fsdevel@...r.kernel.org, 
 linux-security-module@...r.kernel.org, 
 keescook@...omium.org, 
 kernel-team@...a.com, 
 sargun@...gun.me
Subject: RE: [PATCH bpf-next 1/8] bpf: fail BPF_TOKEN_CREATE if no delegation
 option was set on BPF FS

Andrii Nakryiko wrote:
> It's quite confusing in practice when it's possible to successfully
> create a BPF token from BPF FS that didn't have any of delegate_xxx
> mount options set up. While it's not wrong, it's actually more
> meaningful to reject BPF_TOKEN_CREATE with specific error code (-ENOENT)
> to let user-space know that no token delegation is setup up.
> 
> So, instead of creating empty BPF token that will be always ignored
> because it doesn't have any of the allow_xxx bits set, reject it with
> -ENOENT. If we ever need empty BPF token to be possible, we can support
> that with extra flag passed into BPF_TOKEN_CREATE.
> 
> Signed-off-by: Andrii Nakryiko <andrii@...nel.org>
> ---
>  kernel/bpf/token.c | 10 +++++++++-
>  1 file changed, 9 insertions(+), 1 deletion(-)
> 
> diff --git a/kernel/bpf/token.c b/kernel/bpf/token.c
> index 17212efcde60..a86fccd57e2d 100644
> --- a/kernel/bpf/token.c
> +++ b/kernel/bpf/token.c
> @@ -152,6 +152,15 @@ int bpf_token_create(union bpf_attr *attr)
>  		goto out_path;
>  	}
>  
> +	mnt_opts = path.dentry->d_sb->s_fs_info;
> +	if (mnt_opts->delegate_cmds == 0 &&
> +	    mnt_opts->delegate_maps == 0 &&
> +	    mnt_opts->delegate_progs == 0 &&
> +	    mnt_opts->delegate_attachs == 0) {
> +		err = -ENOENT; /* no BPF token delegation is set up */
> +		goto out_path;
> +	}
> +
>  	mode = S_IFREG | ((S_IRUSR | S_IWUSR) & ~current_umask());
>  	inode = bpf_get_inode(path.mnt->mnt_sb, NULL, mode);
>  	if (IS_ERR(inode)) {
> @@ -181,7 +190,6 @@ int bpf_token_create(union bpf_attr *attr)
>  	/* remember bpffs owning userns for future ns_capable() checks */
>  	token->userns = get_user_ns(userns);
>  
> -	mnt_opts = path.dentry->d_sb->s_fs_info;
>  	token->allowed_cmds = mnt_opts->delegate_cmds;
>  	token->allowed_maps = mnt_opts->delegate_maps;
>  	token->allowed_progs = mnt_opts->delegate_progs;
> -- 
> 2.34.1
> 
> 

Acked-by: John Fastabend <john.fastabend@...il.com>