Stanislav Fomichev <sdf@xxxxxxxxxx> [Tue, 2021-01-26 11:36 -0800]:
> At the moment, BPF_CGROUP_INET{4,6}_BIND hooks can rewrite user_port
> to the privileged ones (< ip_unprivileged_port_start), but it will
> be rejected later on in the __inet_bind or __inet6_bind.
>
> Let's add another return value to indicate that CAP_NET_BIND_SERVICE
> check should be ignored. Use the same idea as we currently use
> in cgroup/egress where bit #1 indicates CN. Instead, for
> cgroup/bind{4,6}, bit #1 indicates that CAP_NET_BIND_SERVICE should
> be bypassed.
>
> v4:
> - Add missing IPv6 support (Martin KaFai Lau)
>
> v3:
> - Update description (Martin KaFai Lau)
> - Fix capability restore in selftest (Martin KaFai Lau)
>
> v2:
> - Switch to explicit return code (Martin KaFai Lau)
>
> Cc: Andrey Ignatov <rdna@xxxxxx>
> Cc: Martin KaFai Lau <kafai@xxxxxx>
> Signed-off-by: Stanislav Fomichev <sdf@xxxxxxxxxx>
Explicit return code looks much cleaner than both what v1 did and what I
proposed earlier (compare port before/after).
Just one nit from me but otherwide looks good.
Acked-by: Andrey Ignatov <rdna@xxxxxx>
...
> @@ -231,30 +232,48 @@ int bpf_percpu_cgroup_storage_update(struct bpf_map *map, void *key,
>
> #define BPF_CGROUP_RUN_SA_PROG(sk, uaddr, type) \
> ({ \
> + u32 __unused_flags; \
> int __ret = 0; \
> if (cgroup_bpf_enabled(type)) \
> __ret = __cgroup_bpf_run_filter_sock_addr(sk, uaddr, type, \
> - NULL); \
> + NULL, \
> + &__unused_flags); \
> __ret; \
> })
>
> #define BPF_CGROUP_RUN_SA_PROG_LOCK(sk, uaddr, type, t_ctx) \
> ({ \
> + u32 __unused_flags; \
> int __ret = 0; \
> if (cgroup_bpf_enabled(type)) { \
> lock_sock(sk); \
> __ret = __cgroup_bpf_run_filter_sock_addr(sk, uaddr, type, \
> - t_ctx); \
> + t_ctx, \
> + &__unused_flags); \
> release_sock(sk); \
> } \
> __ret; \
> })
>
> -#define BPF_CGROUP_RUN_PROG_INET4_BIND_LOCK(sk, uaddr) \
> - BPF_CGROUP_RUN_SA_PROG_LOCK(sk, uaddr, BPF_CGROUP_INET4_BIND, NULL)
> -
> -#define BPF_CGROUP_RUN_PROG_INET6_BIND_LOCK(sk, uaddr) \
> - BPF_CGROUP_RUN_SA_PROG_LOCK(sk, uaddr, BPF_CGROUP_INET6_BIND, NULL)
> +/* BPF_CGROUP_INET4_BIND and BPF_CGROUP_INET6_BIND can return extra flags
> + * via upper bits of return code. The only flag that is supported
> + * (at bit position 0) is to indicate CAP_NET_BIND_SERVICE capability check
> + * should be bypassed.
> + */
> +#define BPF_CGROUP_RUN_PROG_INET_BIND_LOCK(sk, uaddr, type, flags) \
> +({ \
> + u32 __flags = 0; \
> + int __ret = 0; \
> + if (cgroup_bpf_enabled(type)) { \
> + lock_sock(sk); \
> + __ret = __cgroup_bpf_run_filter_sock_addr(sk, uaddr, type, \
> + NULL, &__flags); \
> + release_sock(sk); \
> + if (__flags & 1) \
> + *flags |= BIND_NO_CAP_NET_BIND_SERVICE; \
Nit: It took me some time to realize that there are two different
"flags": one to pass to __cgroup_bpf_run_filter_sock_addr() and another
to pass to __inet{,6}_bind/BPF_CGROUP_RUN_PROG_INET_BIND_LOCK that both carry
"BIND_NO_CAP_NET_BIND_SERVICE" flag but do it differently:
* hard-coded 0x1 in the former case;
* and BIND_NO_CAP_NET_BIND_SERVICE == (1 << 3) in the latter.
I'm not sure how to make it more readable: maybe name `flags` and
`__flags` differently to highlight the difference (`bind_flags` and
`__flags`?) and add a #define for the "1" here?
In anycase IMO it's not worth a respin and can be addressed by a
follow-up if you agree.
> + } \
> + __ret; \
> +})
>
> #define BPF_CGROUP_PRE_CONNECT_ENABLED(sk) \
> ((cgroup_bpf_enabled(BPF_CGROUP_INET4_CONNECT) || \
--
Andrey Ignatov
