Commit 46f8bc92 authored by Martin KaFai Lau's avatar Martin KaFai Lau Committed by Alexei Starovoitov
Browse files

bpf: Add a bpf_sock pointer to __sk_buff and a bpf_sk_fullsock helper 



In kernel, it is common to check "skb->sk && sk_fullsock(skb->sk)"
before accessing the fields in sock.  For example, in __netdev_pick_tx:

static u16 __netdev_pick_tx(struct net_device *dev, struct sk_buff *skb,
			    struct net_device *sb_dev)
{
	/* ... */

	struct sock *sk = skb->sk;

		if (queue_index != new_index && sk &&
		    sk_fullsock(sk) &&
		    rcu_access_pointer(sk->sk_dst_cache))
			sk_tx_queue_set(sk, new_index);

	/* ... */

	return queue_index;
}

This patch adds a "struct bpf_sock *sk" pointer to the "struct __sk_buff"
where a few of the convert_ctx_access() in filter.c has already been
accessing the skb->sk sock_common's fields,
e.g. sock_ops_convert_ctx_access().

"__sk_buff->sk" is a PTR_TO_SOCK_COMMON_OR_NULL in the verifier.
Some of the fileds in "bpf_sock" will not be directly
accessible through the "__sk_buff->sk" pointer.  It is limited
by the new "bpf_sock_common_is_valid_access()".
e.g. The existing "type", "protocol", "mark" and "priority" in bpf_sock
     are not allowed.

The newly added "struct bpf_sock *bpf_sk_fullsock(struct bpf_sock *sk)"
can be used to get a sk with all accessible fields in "bpf_sock".
This helper is added to both cg_skb and sched_(cls|act).

int cg_skb_foo(struct __sk_buff *skb) {
	struct bpf_sock *sk;

	sk = skb->sk;
	if (!sk)
		return 1;

	sk = bpf_sk_fullsock(sk);
	if (!sk)
		return 1;

	if (sk->family != AF_INET6 || sk->protocol != IPPROTO_TCP)
		return 1;

	/* some_traffic_shaping(); */

	return 1;
}

(1) The sk is read only

(2) There is no new "struct bpf_sock_common" introduced.

(3) Future kernel sock's members could be added to bpf_sock only
    instead of repeatedly adding at multiple places like currently
    in bpf_sock_ops_md, bpf_sock_addr_md, sk_reuseport_md...etc.

(4) After "sk = skb->sk", the reg holding sk is in type
    PTR_TO_SOCK_COMMON_OR_NULL.

(5) After bpf_sk_fullsock(), the return type will be in type
    PTR_TO_SOCKET_OR_NULL which is the same as the return type of
    bpf_sk_lookup_xxx().

    However, bpf_sk_fullsock() does not take refcnt.  The
    acquire_reference_state() is only depending on the return type now.
    To avoid it, a new is_acquire_function() is checked before calling
    acquire_reference_state().

(6) The WARN_ON in "release_reference_state()" is no longer an
    internal verifier bug.

    When reg->id is not found in state->refs[], it means the
    bpf_prog does something wrong like
    "bpf_sk_release(bpf_sk_fullsock(skb->sk))" where reference has
    never been acquired by calling "bpf_sk_fullsock(skb->sk)".

    A -EINVAL and a verbose are done instead of WARN_ON.  A test is
    added to the test_verifier in a later patch.

    Since the WARN_ON in "release_reference_state()" is no longer
    needed, "__release_reference_state()" is folded into
    "release_reference_state()" also.

Acked-by: default avatarAlexei Starovoitov <ast@kernel.org>
Signed-off-by: default avatarMartin KaFai Lau <kafai@fb.com>
Signed-off-by: default avatarAlexei Starovoitov <ast@kernel.org>
parent 5f456649

include/linux/bpf.h

+12 −0
Original line number Diff line number Diff line
@@ -194,6 +194,7 @@ enum bpf_arg_type { 
	ARG_ANYTHING,		/* any (initialized) argument is ok */

	ARG_PTR_TO_SOCKET,	/* pointer to bpf_sock */

	ARG_PTR_TO_SPIN_LOCK,	/* pointer to bpf_spin_lock */

	ARG_PTR_TO_SOCK_COMMON,	/* pointer to sock_common */

};



/* type of values returned from helper functions */
@@ -256,6 +257,8 @@ enum bpf_reg_type { 
	PTR_TO_FLOW_KEYS,	 /* reg points to bpf_flow_keys */

	PTR_TO_SOCKET,		 /* reg points to struct bpf_sock */

	PTR_TO_SOCKET_OR_NULL,	 /* reg points to struct bpf_sock or NULL */

	PTR_TO_SOCK_COMMON,	 /* reg points to sock_common */

	PTR_TO_SOCK_COMMON_OR_NULL, /* reg points to sock_common or NULL */

};



/* The information passed from prog-specific *_is_valid_access
@@ -920,6 +923,9 @@ void bpf_user_rnd_init_once(void); 
u64 bpf_user_rnd_u32(u64 r1, u64 r2, u64 r3, u64 r4, u64 r5);



#if defined(CONFIG_NET)

bool bpf_sock_common_is_valid_access(int off, int size,

				     enum bpf_access_type type,

				     struct bpf_insn_access_aux *info);

bool bpf_sock_is_valid_access(int off, int size, enum bpf_access_type type,

			      struct bpf_insn_access_aux *info);

u32 bpf_sock_convert_ctx_access(enum bpf_access_type type,
@@ -928,6 +934,12 @@ u32 bpf_sock_convert_ctx_access(enum bpf_access_type type, 
				struct bpf_prog *prog,

				u32 *target_size);

#else

static inline bool bpf_sock_common_is_valid_access(int off, int size,

						   enum bpf_access_type type,

						   struct bpf_insn_access_aux *info)

{

	return false;

}

static inline bool bpf_sock_is_valid_access(int off, int size,

					    enum bpf_access_type type,

					    struct bpf_insn_access_aux *info)

include/uapi/linux/bpf.h

+11 −1
Original line number Diff line number Diff line
@@ -2329,6 +2329,14 @@ union bpf_attr { 
 *		"**y**".

 *	Return

 *		0

 *

 * struct bpf_sock *bpf_sk_fullsock(struct bpf_sock *sk)

 *	Description

 *		This helper gets a **struct bpf_sock** pointer such

 *		that all the fields in bpf_sock can be accessed.

 *	Return

 *		A **struct bpf_sock** pointer on success, or NULL in

 *		case of failure.

 */

#define __BPF_FUNC_MAPPER(FN)		\

	FN(unspec),			\
@@ -2425,7 +2433,8 @@ union bpf_attr { 
	FN(msg_pop_data),		\

	FN(rc_pointer_rel),		\

	FN(spin_lock),			\

	FN(spin_unlock),

	FN(spin_unlock),		\

	FN(sk_fullsock),



/* integer value in 'imm' field of BPF_CALL instruction selects which helper

 * function eBPF program intends to call
@@ -2545,6 +2554,7 @@ struct __sk_buff { 
	__u64 tstamp;

	__u32 wire_len;

	__u32 gso_segs;

	__bpf_md_ptr(struct bpf_sock *, sk);

};



struct bpf_tunnel_key {

kernel/bpf/verifier.c

+92 −40
Original line number Diff line number Diff line
@@ -331,10 +331,17 @@ static bool type_is_pkt_pointer(enum bpf_reg_type type) 
	       type == PTR_TO_PACKET_META;

}



static bool type_is_sk_pointer(enum bpf_reg_type type)

{

	return type == PTR_TO_SOCKET ||

		type == PTR_TO_SOCK_COMMON;

}



static bool reg_type_may_be_null(enum bpf_reg_type type)

{

	return type == PTR_TO_MAP_VALUE_OR_NULL ||

	       type == PTR_TO_SOCKET_OR_NULL;

	       type == PTR_TO_SOCKET_OR_NULL ||

	       type == PTR_TO_SOCK_COMMON_OR_NULL;

}



static bool type_is_refcounted(enum bpf_reg_type type)
@@ -377,6 +384,12 @@ static bool is_release_function(enum bpf_func_id func_id) 
	return func_id == BPF_FUNC_sk_release;

}



static bool is_acquire_function(enum bpf_func_id func_id)

{

	return func_id == BPF_FUNC_sk_lookup_tcp ||

		func_id == BPF_FUNC_sk_lookup_udp;

}



/* string representation of 'enum bpf_reg_type' */

static const char * const reg_type_str[] = {

	[NOT_INIT]		= "?",
@@ -392,6 +405,8 @@ static const char * const reg_type_str[] = { 
	[PTR_TO_FLOW_KEYS]	= "flow_keys",

	[PTR_TO_SOCKET]		= "sock",

	[PTR_TO_SOCKET_OR_NULL] = "sock_or_null",

	[PTR_TO_SOCK_COMMON]	= "sock_common",

	[PTR_TO_SOCK_COMMON_OR_NULL] = "sock_common_or_null",

};



static char slot_type_char[] = {
@@ -618,13 +633,10 @@ static int acquire_reference_state(struct bpf_verifier_env *env, int insn_idx) 
}



/* release function corresponding to acquire_reference_state(). Idempotent. */

static int __release_reference_state(struct bpf_func_state *state, int ptr_id)

static int release_reference_state(struct bpf_func_state *state, int ptr_id)

{

	int i, last_idx;



	if (!ptr_id)

		return -EFAULT;



	last_idx = state->acquired_refs - 1;

	for (i = 0; i < state->acquired_refs; i++) {

		if (state->refs[i].id == ptr_id) {
@@ -636,21 +648,7 @@ static int __release_reference_state(struct bpf_func_state *state, int ptr_id) 
			return 0;

		}

	}

	return -EFAULT;

}



/* variation on the above for cases where we expect that there must be an

 * outstanding reference for the specified ptr_id.

 */

static int release_reference_state(struct bpf_verifier_env *env, int ptr_id)

{

	struct bpf_func_state *state = cur_func(env);

	int err;



	err = __release_reference_state(state, ptr_id);

	if (WARN_ON_ONCE(err != 0))

		verbose(env, "verifier internal error: can't release reference\n");

	return err;

	return -EINVAL;

}



static int transfer_reference_state(struct bpf_func_state *dst,
@@ -1209,6 +1207,8 @@ static bool is_spillable_regtype(enum bpf_reg_type type) 
	case CONST_PTR_TO_MAP:

	case PTR_TO_SOCKET:

	case PTR_TO_SOCKET_OR_NULL:

	case PTR_TO_SOCK_COMMON:

	case PTR_TO_SOCK_COMMON_OR_NULL:

		return true;

	default:

		return false;
@@ -1647,6 +1647,7 @@ static int check_sock_access(struct bpf_verifier_env *env, int insn_idx, 
	struct bpf_reg_state *regs = cur_regs(env);

	struct bpf_reg_state *reg = &regs[regno];

	struct bpf_insn_access_aux info = {};

	bool valid;



	if (reg->smin_value < 0) {

		verbose(env, "R%d min value is negative, either use unsigned index or do a if (index >=0) check.\n",
@@ -1654,17 +1655,30 @@ static int check_sock_access(struct bpf_verifier_env *env, int insn_idx, 
		return -EACCES;

	}



	if (!bpf_sock_is_valid_access(off, size, t, &info)) {

		verbose(env, "invalid bpf_sock access off=%d size=%d\n",

			off, size);

		return -EACCES;

	switch (reg->type) {

	case PTR_TO_SOCK_COMMON:

		valid = bpf_sock_common_is_valid_access(off, size, t, &info);

		break;

	case PTR_TO_SOCKET:

		valid = bpf_sock_is_valid_access(off, size, t, &info);

		break;

	default:

		valid = false;

	}



	env->insn_aux_data[insn_idx].ctx_field_size = info.ctx_field_size;



	if (valid) {

		env->insn_aux_data[insn_idx].ctx_field_size =

			info.ctx_field_size;

		return 0;

	}



	verbose(env, "R%d invalid %s access off=%d size=%d\n",

		regno, reg_type_str[reg->type], off, size);



	return -EACCES;

}



static bool __is_pointer_value(bool allow_ptr_leaks,

			       const struct bpf_reg_state *reg)

{
@@ -1688,8 +1702,14 @@ static bool is_ctx_reg(struct bpf_verifier_env *env, int regno) 
{

	const struct bpf_reg_state *reg = reg_state(env, regno);



	return reg->type == PTR_TO_CTX ||

	       reg->type == PTR_TO_SOCKET;

	return reg->type == PTR_TO_CTX;

}



static bool is_sk_reg(struct bpf_verifier_env *env, int regno)

{

	const struct bpf_reg_state *reg = reg_state(env, regno);



	return type_is_sk_pointer(reg->type);

}



static bool is_pkt_reg(struct bpf_verifier_env *env, int regno)
@@ -1800,6 +1820,9 @@ static int check_ptr_alignment(struct bpf_verifier_env *env, 
	case PTR_TO_SOCKET:

		pointer_desc = "sock ";

		break;

	case PTR_TO_SOCK_COMMON:

		pointer_desc = "sock_common ";

		break;

	default:

		break;

	}
@@ -2003,11 +2026,14 @@ static int check_mem_access(struct bpf_verifier_env *env, int insn_idx, u32 regn 
			 * PTR_TO_PACKET[_META,_END]. In the latter

			 * case, we know the offset is zero.

			 */

			if (reg_type == SCALAR_VALUE)

			if (reg_type == SCALAR_VALUE) {

				mark_reg_unknown(env, regs, value_regno);

			else

			} else {

				mark_reg_known_zero(env, regs,

						    value_regno);

				if (reg_type_may_be_null(reg_type))

					regs[value_regno].id = ++env->id_gen;

			}

			regs[value_regno].type = reg_type;

		}
@@ -2053,9 +2079,10 @@ static int check_mem_access(struct bpf_verifier_env *env, int insn_idx, u32 regn 
		err = check_flow_keys_access(env, off, size);

		if (!err && t == BPF_READ && value_regno >= 0)

			mark_reg_unknown(env, regs, value_regno);

	} else if (reg->type == PTR_TO_SOCKET) {

	} else if (type_is_sk_pointer(reg->type)) {

		if (t == BPF_WRITE) {

			verbose(env, "cannot write into socket\n");

			verbose(env, "R%d cannot write into %s\n",

				regno, reg_type_str[reg->type]);

			return -EACCES;

		}

		err = check_sock_access(env, insn_idx, regno, off, size, t);
@@ -2102,7 +2129,8 @@ static int check_xadd(struct bpf_verifier_env *env, int insn_idx, struct bpf_ins 


	if (is_ctx_reg(env, insn->dst_reg) ||

	    is_pkt_reg(env, insn->dst_reg) ||

	    is_flow_key_reg(env, insn->dst_reg)) {

	    is_flow_key_reg(env, insn->dst_reg) ||

	    is_sk_reg(env, insn->dst_reg)) {

		verbose(env, "BPF_XADD stores into R%d %s is not allowed\n",

			insn->dst_reg,

			reg_type_str[reg_state(env, insn->dst_reg)->type]);
@@ -2369,6 +2397,11 @@ static int check_func_arg(struct bpf_verifier_env *env, u32 regno, 
		err = check_ctx_reg(env, reg, regno);

		if (err < 0)

			return err;

	} else if (arg_type == ARG_PTR_TO_SOCK_COMMON) {

		expected_type = PTR_TO_SOCK_COMMON;

		/* Any sk pointer can be ARG_PTR_TO_SOCK_COMMON */

		if (!type_is_sk_pointer(type))

			goto err_type;

	} else if (arg_type == ARG_PTR_TO_SOCKET) {

		expected_type = PTR_TO_SOCKET;

		if (type != expected_type)
@@ -2783,7 +2816,7 @@ static int release_reference(struct bpf_verifier_env *env, 
	for (i = 0; i <= vstate->curframe; i++)

		release_reg_references(env, vstate->frame[i], meta->ptr_id);



	return release_reference_state(env, meta->ptr_id);

	return release_reference_state(cur_func(env), meta->ptr_id);

}



static int check_func_call(struct bpf_verifier_env *env, struct bpf_insn *insn,
@@ -3049,9 +3082,12 @@ static int check_helper_call(struct bpf_verifier_env *env, int func_id, int insn 
		}

	} else if (is_release_function(func_id)) {

		err = release_reference(env, &meta);

		if (err)

		if (err) {

			verbose(env, "func %s#%d reference has not been acquired before\n",

				func_id_name(func_id), func_id);

			return err;

		}

	}



	regs = cur_regs(env);
@@ -3099,12 +3135,19 @@ static int check_helper_call(struct bpf_verifier_env *env, int func_id, int insn 
			regs[BPF_REG_0].id = ++env->id_gen;

		}

	} else if (fn->ret_type == RET_PTR_TO_SOCKET_OR_NULL) {

		mark_reg_known_zero(env, regs, BPF_REG_0);

		regs[BPF_REG_0].type = PTR_TO_SOCKET_OR_NULL;

		if (is_acquire_function(func_id)) {

			int id = acquire_reference_state(env, insn_idx);



			if (id < 0)

				return id;

		mark_reg_known_zero(env, regs, BPF_REG_0);

		regs[BPF_REG_0].type = PTR_TO_SOCKET_OR_NULL;

			/* For release_reference() */

			regs[BPF_REG_0].id = id;

		} else {

			/* For mark_ptr_or_null_reg() */

			regs[BPF_REG_0].id = ++env->id_gen;

		}

	} else {

		verbose(env, "unknown return type %d of func %s#%d\n",

			fn->ret_type, func_id_name(func_id), func_id);
@@ -3364,6 +3407,8 @@ static int adjust_ptr_min_max_vals(struct bpf_verifier_env *env, 
	case PTR_TO_PACKET_END:

	case PTR_TO_SOCKET:

	case PTR_TO_SOCKET_OR_NULL:

	case PTR_TO_SOCK_COMMON:

	case PTR_TO_SOCK_COMMON_OR_NULL:

		verbose(env, "R%d pointer arithmetic on %s prohibited\n",

			dst, reg_type_str[ptr_reg->type]);

		return -EACCES;
@@ -4597,6 +4642,8 @@ static void mark_ptr_or_null_reg(struct bpf_func_state *state, 
			}

		} else if (reg->type == PTR_TO_SOCKET_OR_NULL) {

			reg->type = PTR_TO_SOCKET;

		} else if (reg->type == PTR_TO_SOCK_COMMON_OR_NULL) {

			reg->type = PTR_TO_SOCK_COMMON;

		}

		if (is_null || !(reg_is_refcounted(reg) ||

				 reg_may_point_to_spin_lock(reg))) {
@@ -4621,7 +4668,7 @@ static void mark_ptr_or_null_regs(struct bpf_verifier_state *vstate, u32 regno, 
	int i, j;



	if (reg_is_refcounted_or_null(&regs[regno]) && is_null)

		__release_reference_state(state, id);

		release_reference_state(state, id);



	for (i = 0; i < MAX_BPF_REG; i++)

		mark_ptr_or_null_reg(state, &regs[i], id, is_null);
@@ -5790,6 +5837,8 @@ static bool regsafe(struct bpf_reg_state *rold, struct bpf_reg_state *rcur, 
	case PTR_TO_FLOW_KEYS:

	case PTR_TO_SOCKET:

	case PTR_TO_SOCKET_OR_NULL:

	case PTR_TO_SOCK_COMMON:

	case PTR_TO_SOCK_COMMON_OR_NULL:

		/* Only valid matches are exact, which memcmp() above

		 * would have accepted

		 */
@@ -6110,6 +6159,8 @@ static bool reg_type_mismatch_ok(enum bpf_reg_type type) 
	case PTR_TO_CTX:

	case PTR_TO_SOCKET:

	case PTR_TO_SOCKET_OR_NULL:

	case PTR_TO_SOCK_COMMON:

	case PTR_TO_SOCK_COMMON_OR_NULL:

		return false;

	default:

		return true;
@@ -7112,6 +7163,7 @@ static int convert_ctx_accesses(struct bpf_verifier_env *env) 
			convert_ctx_access = ops->convert_ctx_access;

			break;

		case PTR_TO_SOCKET:

		case PTR_TO_SOCK_COMMON:

			convert_ctx_access = bpf_sock_convert_ctx_access;

			break;

		default:

net/core/filter.c

+42 −0
Original line number Diff line number Diff line
@@ -1793,6 +1793,20 @@ static const struct bpf_func_proto bpf_skb_pull_data_proto = { 
	.arg2_type	= ARG_ANYTHING,

};



BPF_CALL_1(bpf_sk_fullsock, struct sock *, sk)

{

	sk = sk_to_full_sk(sk);



	return sk_fullsock(sk) ? (unsigned long)sk : (unsigned long)NULL;

}



static const struct bpf_func_proto bpf_sk_fullsock_proto = {

	.func		= bpf_sk_fullsock,

	.gpl_only	= false,

	.ret_type	= RET_PTR_TO_SOCKET_OR_NULL,

	.arg1_type	= ARG_PTR_TO_SOCK_COMMON,

};



static inline int sk_skb_try_make_writable(struct sk_buff *skb,

					   unsigned int write_len)

{
@@ -5406,6 +5420,8 @@ cg_skb_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog) 
	switch (func_id) {

	case BPF_FUNC_get_local_storage:

		return &bpf_get_local_storage_proto;

	case BPF_FUNC_sk_fullsock:

		return &bpf_sk_fullsock_proto;

	default:

		return sk_filter_func_proto(func_id, prog);

	}
@@ -5477,6 +5493,8 @@ tc_cls_act_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog) 
		return &bpf_get_socket_uid_proto;

	case BPF_FUNC_fib_lookup:

		return &bpf_skb_fib_lookup_proto;

	case BPF_FUNC_sk_fullsock:

		return &bpf_sk_fullsock_proto;

#ifdef CONFIG_XFRM

	case BPF_FUNC_skb_get_xfrm_state:

		return &bpf_skb_get_xfrm_state_proto;
@@ -5764,6 +5782,11 @@ static bool bpf_skb_is_valid_access(int off, int size, enum bpf_access_type type 
		if (size != sizeof(__u64))

			return false;

		break;

	case offsetof(struct __sk_buff, sk):

		if (type == BPF_WRITE || size != sizeof(__u64))

			return false;

		info->reg_type = PTR_TO_SOCK_COMMON_OR_NULL;

		break;

	default:

		/* Only narrow read access allowed for now. */

		if (type == BPF_WRITE) {
@@ -5950,6 +5973,18 @@ static bool __sock_filter_check_size(int off, int size, 
	return size == size_default;

}



bool bpf_sock_common_is_valid_access(int off, int size,

				     enum bpf_access_type type,

				     struct bpf_insn_access_aux *info)

{

	switch (off) {

	case bpf_ctx_range_till(struct bpf_sock, type, priority):

		return false;

	default:

		return bpf_sock_is_valid_access(off, size, type, info);

	}

}



bool bpf_sock_is_valid_access(int off, int size, enum bpf_access_type type,

			      struct bpf_insn_access_aux *info)

{
@@ -6748,6 +6783,13 @@ static u32 bpf_convert_ctx_access(enum bpf_access_type type, 
		off += offsetof(struct qdisc_skb_cb, pkt_len);

		*target_size = 4;

		*insn++ = BPF_LDX_MEM(BPF_W, si->dst_reg, si->src_reg, off);

		break;



	case offsetof(struct __sk_buff, sk):

		*insn++ = BPF_LDX_MEM(BPF_FIELD_SIZEOF(struct sk_buff, sk),

				      si->dst_reg, si->src_reg,

				      offsetof(struct sk_buff, sk));

		break;

	}



	return insn - insn_buf;

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