linux-kernel - Re: [PATCH bpf-next 2/3] net: sysctl: No need to check CAP_SYS_ADMIN for bpf_jit

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Date:   Mon, 9 May 2022 17:02:10 +0200
From:   Daniel Borkmann <daniel@...earbox.net>
To:     Tiezhu Yang <yangtiezhu@...ngson.cn>, davem@...emloft.net,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        Alexei Starovoitov <ast@...nel.org>,
        Andrii Nakryiko <andrii@...nel.org>
Cc:     netdev@...r.kernel.org, bpf@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH bpf-next 2/3] net: sysctl: No need to check CAP_SYS_ADMIN
 for bpf_jit_*

On 5/9/22 8:57 AM, Tiezhu Yang wrote:
> The mode of the following procnames are defined as 0644, 0600, 0600
> and 0600 respectively in net_core_table[], normal user can not write
> them, so no need to check CAP_SYS_ADMIN in the related proc_handler
> function, just remove the checks.
> 
> /proc/sys/net/core/bpf_jit_enable
> /proc/sys/net/core/bpf_jit_harden
> /proc/sys/net/core/bpf_jit_kallsyms
> /proc/sys/net/core/bpf_jit_limit
> 
> Signed-off-by: Tiezhu Yang <yangtiezhu@...ngson.cn>

I don't think we can make this assumption - there are various other (non-BPF)
sysctl handlers in the tree doing similar check to prevent from userns' based
CAP_SYS_ADMIN.

> ---
>   net/core/sysctl_net_core.c | 9 ---------
>   1 file changed, 9 deletions(-)
> 
> diff --git a/net/core/sysctl_net_core.c b/net/core/sysctl_net_core.c
> index cf00dd7..059352b 100644
> --- a/net/core/sysctl_net_core.c
> +++ b/net/core/sysctl_net_core.c
> @@ -268,9 +268,6 @@ static int proc_dointvec_minmax_bpf_enable(struct ctl_table *table, int write,
>   	int ret, jit_enable = *(int *)table->data;
>   	struct ctl_table tmp = *table;
>   
> -	if (write && !capable(CAP_SYS_ADMIN))
> -		return -EPERM;
> -
>   	tmp.data = &jit_enable;
>   	ret = proc_dointvec_minmax(&tmp, write, buffer, lenp, ppos);
>   	if (write && !ret) {
> @@ -291,9 +288,6 @@ static int
>   proc_dointvec_minmax_bpf_restricted(struct ctl_table *table, int write,
>   				    void *buffer, size_t *lenp, loff_t *ppos)
>   {
> -	if (!capable(CAP_SYS_ADMIN))
> -		return -EPERM;
> -
>   	return proc_dointvec_minmax(table, write, buffer, lenp, ppos);
>   }
>   # endif /* CONFIG_HAVE_EBPF_JIT */
> @@ -302,9 +296,6 @@ static int
>   proc_dolongvec_minmax_bpf_restricted(struct ctl_table *table, int write,
>   				     void *buffer, size_t *lenp, loff_t *ppos)
>   {
> -	if (!capable(CAP_SYS_ADMIN))
> -		return -EPERM;
> -
>   	return proc_doulongvec_minmax(table, write, buffer, lenp, ppos);
>   }
>   #endif
>