netdev - Re: [PATCH bpf] bpf: respect CAP_IPC_LOCK in RLIMIT

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Date:   Fri, 13 Sep 2019 18:48:53 +0000
From:   Yonghong Song <yhs@...com>
To:     Christian Barcenas <christian@...rcenas.com>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>
CC:     Martin Lau <kafai@...com>, Song Liu <songliubraving@...com>,
        "bpf@...r.kernel.org" <bpf@...r.kernel.org>
Subject: Re: [PATCH bpf] bpf: respect CAP_IPC_LOCK in RLIMIT_MEMLOCK check



On 9/11/19 7:18 PM, Christian Barcenas wrote:
> A process can lock memory addresses into physical RAM explicitly
> (via mlock, mlockall, shmctl, etc.) or implicitly (via VFIO,
> perf ring-buffers, bpf maps, etc.), subject to RLIMIT_MEMLOCK limits.
> 
> CAP_IPC_LOCK allows a process to exceed these limits, and throughout
> the kernel this capability is checked before allowing/denying an attempt
> to lock memory regions into RAM.
> 
> Because bpf locks its programs and maps into RAM, it should respect
> CAP_IPC_LOCK. Previously, bpf would return EPERM when RLIMIT_MEMLOCK was
> exceeded by a privileged process, which is contrary to documented
> RLIMIT_MEMLOCK+CAP_IPC_LOCK behavior.
> 
> Fixes: aaac3ba95e4c ("bpf: charge user for creation of BPF maps and programs")
> Signed-off-by: Christian Barcenas <christian@...rcenas.com>

Acked-by: Yonghong Song <yhs@...com>

> ---
>   kernel/bpf/syscall.c | 5 +++--
>   1 file changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
> index 272071e9112f..e551961f364b 100644
> --- a/kernel/bpf/syscall.c
> +++ b/kernel/bpf/syscall.c
> @@ -183,8 +183,9 @@ void bpf_map_init_from_attr(struct bpf_map *map, union bpf_attr *attr)
>   static int bpf_charge_memlock(struct user_struct *user, u32 pages)
>   {
>   	unsigned long memlock_limit = rlimit(RLIMIT_MEMLOCK) >> PAGE_SHIFT;
> +	unsigned long locked = atomic_long_add_return(pages, &user->locked_vm);
>   
> -	if (atomic_long_add_return(pages, &user->locked_vm) > memlock_limit) {
> +	if (locked > memlock_limit && !capable(CAP_IPC_LOCK)) {
>   		atomic_long_sub(pages, &user->locked_vm);
>   		return -EPERM;
>   	}
> @@ -1231,7 +1232,7 @@ int __bpf_prog_charge(struct user_struct *user, u32 pages)
>   
>   	if (user) {
>   		user_bufs = atomic_long_add_return(pages, &user->locked_vm);
> -		if (user_bufs > memlock_limit) {
> +		if (user_bufs > memlock_limit && !capable(CAP_IPC_LOCK)) {
>   			atomic_long_sub(pages, &user->locked_vm);
>   			return -EPERM;
>   		}
>