Commit 77241217 authored by Stanislav Fomichev's avatar Stanislav Fomichev Committed by Alexei Starovoitov
Browse files

bpf: Allow rewriting to ports under ip_unprivileged_port_start 



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.

v5:
- rename flags to be less confusing (Andrey Ignatov)
- rework BPF_PROG_CGROUP_INET_EGRESS_RUN_ARRAY to work on flags
  and accept BPF_RET_SET_CN (no behavioral changes)

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)

Signed-off-by: default avatarStanislav Fomichev <sdf@google.com>
Signed-off-by: default avatarAlexei Starovoitov <ast@kernel.org>
Reviewed-by: default avatarMartin KaFai Lau <kafai@fb.com>
Acked-by: default avatarAndrey Ignatov <rdna@fb.com>
Link: https://lore.kernel.org/bpf/20210127193140.3170382-1-sdf@google.com
parent 8063e184

include/linux/bpf-cgroup.h

+28 −10
Original line number Diff line number Diff line
@@ -125,7 +125,8 @@ int __cgroup_bpf_run_filter_sk(struct sock *sk, 
int __cgroup_bpf_run_filter_sock_addr(struct sock *sk,

				      struct sockaddr *uaddr,

				      enum bpf_attach_type type,

				      void *t_ctx);

				      void *t_ctx,

				      u32 *flags);



int __cgroup_bpf_run_filter_sock_ops(struct sock *sk,

				     struct bpf_sock_ops_kern *sock_ops,
@@ -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 (BPF_RET_BIND_NO_CAP_NET_BIND_SERVICE).

 */

#define BPF_CGROUP_RUN_PROG_INET_BIND_LOCK(sk, uaddr, type, bind_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 & BPF_RET_BIND_NO_CAP_NET_BIND_SERVICE)	       \

			*bind_flags |= BIND_NO_CAP_NET_BIND_SERVICE;	       \

	}								       \

	__ret;								       \

})



#define BPF_CGROUP_PRE_CONNECT_ENABLED(sk)				       \

	((cgroup_bpf_enabled(BPF_CGROUP_INET4_CONNECT) ||		       \
@@ -453,8 +472,7 @@ static inline int bpf_percpu_cgroup_storage_update(struct bpf_map *map, 
#define BPF_CGROUP_RUN_PROG_INET_EGRESS(sk,skb) ({ 0; })

#define BPF_CGROUP_RUN_PROG_INET_SOCK(sk) ({ 0; })

#define BPF_CGROUP_RUN_PROG_INET_SOCK_RELEASE(sk) ({ 0; })

#define BPF_CGROUP_RUN_PROG_INET4_BIND_LOCK(sk, uaddr) ({ 0; })

#define BPF_CGROUP_RUN_PROG_INET6_BIND_LOCK(sk, uaddr) ({ 0; })

#define BPF_CGROUP_RUN_PROG_INET_BIND_LOCK(sk, uaddr, type, flags) ({ 0; })

#define BPF_CGROUP_RUN_PROG_INET4_POST_BIND(sk) ({ 0; })

#define BPF_CGROUP_RUN_PROG_INET6_POST_BIND(sk) ({ 0; })

#define BPF_CGROUP_RUN_PROG_INET4_CONNECT(sk, uaddr) ({ 0; })

include/linux/bpf.h

+33 −19
Original line number Diff line number Diff line
@@ -1073,6 +1073,34 @@ int bpf_prog_array_copy(struct bpf_prog_array *old_array, 
			struct bpf_prog *include_prog,

			struct bpf_prog_array **new_array);



/* BPF program asks to bypass CAP_NET_BIND_SERVICE in bind. */

#define BPF_RET_BIND_NO_CAP_NET_BIND_SERVICE			(1 << 0)

/* BPF program asks to set CN on the packet. */

#define BPF_RET_SET_CN						(1 << 0)



#define BPF_PROG_RUN_ARRAY_FLAGS(array, ctx, func, ret_flags)		\

	({								\

		struct bpf_prog_array_item *_item;			\

		struct bpf_prog *_prog;					\

		struct bpf_prog_array *_array;				\

		u32 _ret = 1;						\

		u32 func_ret;						\

		migrate_disable();					\

		rcu_read_lock();					\

		_array = rcu_dereference(array);			\

		_item = &_array->items[0];				\

		while ((_prog = READ_ONCE(_item->prog))) {		\

			bpf_cgroup_storage_set(_item->cgroup_storage);	\

			func_ret = func(_prog, ctx);			\

			_ret &= (func_ret & 1);				\

			*(ret_flags) |= (func_ret >> 1);			\

			_item++;					\

		}							\

		rcu_read_unlock();					\

		migrate_enable();					\

		_ret;							\

	 })



#define __BPF_PROG_RUN_ARRAY(array, ctx, func, check_non_null)	\

	({						\

		struct bpf_prog_array_item *_item;	\
@@ -1120,25 +1148,11 @@ _out: \ 
 */

#define BPF_PROG_CGROUP_INET_EGRESS_RUN_ARRAY(array, ctx, func)		\

	({						\

		struct bpf_prog_array_item *_item;	\

		struct bpf_prog *_prog;			\

		struct bpf_prog_array *_array;		\

		u32 ret;				\

		u32 _ret = 1;				\

		u32 _cn = 0;				\

		migrate_disable();			\

		rcu_read_lock();			\

		_array = rcu_dereference(array);	\

		_item = &_array->items[0];		\

		while ((_prog = READ_ONCE(_item->prog))) {		\

			bpf_cgroup_storage_set(_item->cgroup_storage);	\

			ret = func(_prog, ctx);		\

			_ret &= (ret & 1);		\

			_cn |= (ret & 2);		\

			_item++;			\

		}					\

		rcu_read_unlock();			\

		migrate_enable();			\

		u32 _flags = 0;				\

		bool _cn;				\

		u32 _ret;				\

		_ret = BPF_PROG_RUN_ARRAY_FLAGS(array, ctx, func, &_flags); \

		_cn = _flags & BPF_RET_SET_CN;		\

		if (_ret)				\

			_ret = (_cn ? NET_XMIT_CN : NET_XMIT_SUCCESS);	\

		else					\

include/net/inet_common.h

+2 −0
Original line number Diff line number Diff line
@@ -41,6 +41,8 @@ int inet_bind(struct socket *sock, struct sockaddr *uaddr, int addr_len); 
#define BIND_WITH_LOCK			(1 << 1)

/* Called from BPF program. */

#define BIND_FROM_BPF			(1 << 2)

/* Skip CAP_NET_BIND_SERVICE check. */

#define BIND_NO_CAP_NET_BIND_SERVICE	(1 << 3)

int __inet_bind(struct sock *sk, struct sockaddr *uaddr, int addr_len,

		u32 flags);

int inet_getname(struct socket *sock, struct sockaddr *uaddr,

kernel/bpf/cgroup.c

+6 −2
Original line number Diff line number Diff line
@@ -1055,6 +1055,8 @@ EXPORT_SYMBOL(__cgroup_bpf_run_filter_sk); 
 * @uaddr: sockaddr struct provided by user

 * @type: The type of program to be exectuted

 * @t_ctx: Pointer to attach type specific context

 * @flags: Pointer to u32 which contains higher bits of BPF program

 *         return value (OR'ed together).

 *

 * socket is expected to be of type INET or INET6.

 *
@@ -1064,7 +1066,8 @@ EXPORT_SYMBOL(__cgroup_bpf_run_filter_sk); 
int __cgroup_bpf_run_filter_sock_addr(struct sock *sk,

				      struct sockaddr *uaddr,

				      enum bpf_attach_type type,

				      void *t_ctx)

				      void *t_ctx,

				      u32 *flags)

{

	struct bpf_sock_addr_kern ctx = {

		.sk = sk,
@@ -1087,7 +1090,8 @@ int __cgroup_bpf_run_filter_sock_addr(struct sock *sk, 
	}



	cgrp = sock_cgroup_ptr(&sk->sk_cgrp_data);

	ret = BPF_PROG_RUN_ARRAY(cgrp->bpf.effective[type], &ctx, BPF_PROG_RUN);

	ret = BPF_PROG_RUN_ARRAY_FLAGS(cgrp->bpf.effective[type], &ctx,

				       BPF_PROG_RUN, flags);



	return ret == 1 ? 0 : -EPERM;

}

kernel/bpf/verifier.c

+3 −0
Original line number Diff line number Diff line
@@ -7986,6 +7986,9 @@ static int check_return_code(struct bpf_verifier_env *env) 
		    env->prog->expected_attach_type == BPF_CGROUP_INET4_GETSOCKNAME ||

		    env->prog->expected_attach_type == BPF_CGROUP_INET6_GETSOCKNAME)

			range = tnum_range(1, 1);

		if (env->prog->expected_attach_type == BPF_CGROUP_INET4_BIND ||

		    env->prog->expected_attach_type == BPF_CGROUP_INET6_BIND)

			range = tnum_range(0, 3);

		break;

	case BPF_PROG_TYPE_CGROUP_SKB:

		if (env->prog->expected_attach_type == BPF_CGROUP_INET_EGRESS) {