Message-Id: <20180509210709.7201-5-joe@wand.net.nz>
Date:   Wed,  9 May 2018 14:07:02 -0700
From:   Joe Stringer <joe@...d.net.nz>
To:     daniel@...earbox.net
Cc:     netdev@...r.kernel.org, ast@...nel.org, john.fastabend@...il.com,
        kafai@...com
Subject: [RFC bpf-next 04/11] bpf: Add PTR_TO_SOCKET verifier type

Teach the verifier a little bit about a new type of pointer, a
PTR_TO_SOCKET. This pointer type is accessed from BPF through the
'struct bpf_sock' structure.

Signed-off-by: Joe Stringer <joe@...d.net.nz>
---
 include/linux/bpf.h          | 19 +++++++++-
 include/linux/bpf_verifier.h |  2 ++
 kernel/bpf/verifier.c        | 86 ++++++++++++++++++++++++++++++++++++++------
 net/core/filter.c            | 30 +++++++++-------
 4 files changed, 114 insertions(+), 23 deletions(-)

diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index a38e474bf7ee..a03b4b0edcb6 100644
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h
@@ -136,7 +136,7 @@ enum bpf_arg_type {
 	/* the following constraints used to prototype bpf_memcmp() and other
 	 * functions that access data on eBPF program stack
 	 */
-	ARG_PTR_TO_MEM,		/* pointer to valid memory (stack, packet, map value) */
+	ARG_PTR_TO_MEM,		/* pointer to valid memory (stack, packet, map value, socket) */
 	ARG_PTR_TO_MEM_OR_NULL, /* pointer to valid memory or NULL */
 	ARG_PTR_TO_UNINIT_MEM,	/* pointer to memory does not need to be initialized,
 				 * helper function must fill all bytes or clear
@@ -148,6 +148,7 @@ enum bpf_arg_type {
 
 	ARG_PTR_TO_CTX,		/* pointer to context */
 	ARG_ANYTHING,		/* any (initialized) argument is ok */
+	ARG_PTR_TO_SOCKET,	/* pointer to bpf_sock */
 };
 
 /* type of values returned from helper functions */
@@ -155,6 +156,7 @@ enum bpf_return_type {
 	RET_INTEGER,			/* function returns integer */
 	RET_VOID,			/* function doesn't return anything */
 	RET_PTR_TO_MAP_VALUE_OR_NULL,	/* returns a pointer to map elem value or NULL */
+	RET_PTR_TO_SOCKET_OR_NULL,	/* returns a pointer to a socket or NULL */
 };
 
 /* eBPF function prototype used by verifier to allow BPF_CALLs from eBPF programs
@@ -205,6 +207,8 @@ enum bpf_reg_type {
 	PTR_TO_PACKET_META,	 /* skb->data - meta_len */
 	PTR_TO_PACKET,		 /* reg points to skb->data */
 	PTR_TO_PACKET_END,	 /* skb->data + headlen */
+	PTR_TO_SOCKET,		 /* reg points to struct bpf_sock */
+	PTR_TO_SOCKET_OR_NULL,	 /* reg points to struct bpf_sock or NULL */
 };
 
 /* The information passed from prog-specific *_is_valid_access
@@ -326,6 +330,11 @@ const struct bpf_func_proto *bpf_get_trace_printk_proto(void);
 
 typedef unsigned long (*bpf_ctx_copy_t)(void *dst, const void *src,
 					unsigned long off, unsigned long len);
+typedef u32 (*bpf_convert_ctx_access_t)(enum bpf_access_type type,
+					const struct bpf_insn *src,
+					struct bpf_insn *dst,
+					struct bpf_prog *prog,
+					u32 *target_size);
 
 u64 bpf_event_output(struct bpf_map *map, u64 flags, void *meta, u64 meta_size,
 		     void *ctx, u64 ctx_size, bpf_ctx_copy_t ctx_copy);
@@ -729,4 +738,12 @@ extern const struct bpf_func_proto bpf_sock_map_update_proto;
 void bpf_user_rnd_init_once(void);
 u64 bpf_user_rnd_u32(u64 r1, u64 r2, u64 r3, u64 r4, u64 r5);
 
+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,
+			        const struct bpf_insn *si,
+			        struct bpf_insn *insn_buf,
+			        struct bpf_prog *prog,
+			        u32 *target_size);
+
 #endif /* _LINUX_BPF_H */
diff --git a/include/linux/bpf_verifier.h b/include/linux/bpf_verifier.h
index a613b52ce939..9dcd87f1d322 100644
--- a/include/linux/bpf_verifier.h
+++ b/include/linux/bpf_verifier.h
@@ -57,6 +57,8 @@ struct bpf_reg_state {
 	 * offset, so they can share range knowledge.
 	 * For PTR_TO_MAP_VALUE_OR_NULL this is used to share which map value we
 	 * came from, when one is tested for != NULL.
+	 * For PTR_TO_SOCKET this is used to share which pointers retain the
+	 * same reference to the socket, to determine proper reference freeing.
 	 */
 	u32 id;
 	/* Ordering of fields matters.  See states_equal() */
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 1b31b805dea4..d38c7c1e9da6 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -80,8 +80,8 @@ static const struct bpf_verifier_ops * const bpf_verifier_ops[] = {
  * (like pointer plus pointer becomes SCALAR_VALUE type)
  *
  * When verifier sees load or store instructions the type of base register
- * can be: PTR_TO_MAP_VALUE, PTR_TO_CTX, PTR_TO_STACK. These are three pointer
- * types recognized by check_mem_access() function.
+ * can be: PTR_TO_MAP_VALUE, PTR_TO_CTX, PTR_TO_STACK, PTR_TO_SOCKET. These are
+ * four pointer types recognized by check_mem_access() function.
  *
  * PTR_TO_MAP_VALUE means that this register is pointing to 'map element value'
  * and the range of [ptr, ptr + map's value_size) is accessible.
@@ -244,6 +244,8 @@ static const char * const reg_type_str[] = {
 	[PTR_TO_PACKET]		= "pkt",
 	[PTR_TO_PACKET_META]	= "pkt_meta",
 	[PTR_TO_PACKET_END]	= "pkt_end",
+	[PTR_TO_SOCKET]		= "sock",
+	[PTR_TO_SOCKET_OR_NULL] = "sock_or_null",
 };
 
 static void print_liveness(struct bpf_verifier_env *env,
@@ -977,6 +979,8 @@ static bool is_spillable_regtype(enum bpf_reg_type type)
 	case PTR_TO_PACKET_META:
 	case PTR_TO_PACKET_END:
 	case CONST_PTR_TO_MAP:
+	case PTR_TO_SOCKET:
+	case PTR_TO_SOCKET_OR_NULL:
 		return true;
 	default:
 		return false;
@@ -1360,6 +1364,28 @@ static int check_ctx_access(struct bpf_verifier_env *env, int insn_idx, int off,
 	return -EACCES;
 }
 
+static int check_sock_access(struct bpf_verifier_env *env, u32 regno, int off,
+			     int size, enum bpf_access_type t)
+{
+	struct bpf_reg_state *regs = cur_regs(env);
+	struct bpf_reg_state *reg = &regs[regno];
+	struct bpf_insn_access_aux info;
+
+	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",
+			regno);
+		return -EACCES;
+	}
+
+	if (!bpf_sock_is_valid_access(off, size, t, &info)) {
+		verbose(env, "invalid bpf_sock_ops access off=%d size=%d\n",
+			off, size);
+		return -EACCES;
+	}
+
+	return 0;
+}
+
 static bool __is_pointer_value(bool allow_ptr_leaks,
 			       const struct bpf_reg_state *reg)
 {
@@ -1475,6 +1501,9 @@ static int check_ptr_alignment(struct bpf_verifier_env *env,
 		 */
 		strict = true;
 		break;
+	case PTR_TO_SOCKET:
+		pointer_desc = "sock ";
+		break;
 	default:
 		break;
 	}
@@ -1723,6 +1752,16 @@ static int check_mem_access(struct bpf_verifier_env *env, int insn_idx, u32 regn
 		err = check_packet_access(env, regno, off, size, false);
 		if (!err && t == BPF_READ && value_regno >= 0)
 			mark_reg_unknown(env, regs, value_regno);
+
+	} else if (reg->type == PTR_TO_SOCKET) {
+		if (t == BPF_WRITE) {
+			verbose(env, "cannot write into socket\n");
+			return -EACCES;
+		}
+		err = check_sock_access(env, regno, off, size, t);
+		if (!err && t == BPF_READ && value_regno >= 0)
+			mark_reg_unknown(env, regs, value_regno);
+
 	} else {
 		verbose(env, "R%d invalid mem access '%s'\n", regno,
 			reg_type_str[reg->type]);
@@ -1941,6 +1980,10 @@ static int check_func_arg(struct bpf_verifier_env *env, u32 regno,
 		expected_type = PTR_TO_CTX;
 		if (type != expected_type)
 			goto err_type;
+	} else if (arg_type == ARG_PTR_TO_SOCKET) {
+		expected_type = PTR_TO_SOCKET;
+		if (type != expected_type)
+			goto err_type;
 	} else if (arg_type_is_mem_ptr(arg_type)) {
 		expected_type = PTR_TO_STACK;
 		/* One exception here. In case function allows for NULL to be
@@ -2477,6 +2520,10 @@ static int check_helper_call(struct bpf_verifier_env *env, int func_id, int insn
 			insn_aux->map_ptr = meta.map_ptr;
 		else if (insn_aux->map_ptr != meta.map_ptr)
 			insn_aux->map_ptr = BPF_MAP_PTR_POISON;
+	} 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;
+		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);
@@ -2614,6 +2661,8 @@ static int adjust_ptr_min_max_vals(struct bpf_verifier_env *env,
 		return -EACCES;
 	case CONST_PTR_TO_MAP:
 	case PTR_TO_PACKET_END:
+	case PTR_TO_SOCKET:
+	case PTR_TO_SOCKET_OR_NULL:
 		verbose(env, "R%d pointer arithmetic on %s prohibited\n",
 			dst, reg_type_str[ptr_reg->type]);
 		return -EACCES;
@@ -3559,6 +3608,8 @@ static void mark_ptr_or_null_reg(struct bpf_reg_state *reg, u32 id,
 			} else {
 				reg->type = PTR_TO_MAP_VALUE;
 			}
+		} else if (reg->type == PTR_TO_SOCKET_OR_NULL) {
+			reg->type = PTR_TO_SOCKET;
 		}
 		/* We don't need id from this point onwards anymore, thus we
 		 * should better reset it, so that state pruning has chances
@@ -4333,6 +4384,8 @@ static bool regsafe(struct bpf_reg_state *rold, struct bpf_reg_state *rcur,
 	case PTR_TO_CTX:
 	case CONST_PTR_TO_MAP:
 	case PTR_TO_PACKET_END:
+	case PTR_TO_SOCKET:
+	case PTR_TO_SOCKET_OR_NULL:
 		/* Only valid matches are exact, which memcmp() above
 		 * would have accepted
 		 */
@@ -5188,10 +5241,14 @@ static void sanitize_dead_code(struct bpf_verifier_env *env)
 	}
 }
 
-/* convert load instructions that access fields of 'struct __sk_buff'
- * into sequence of instructions that access fields of 'struct sk_buff'
+/* convert load instructions that access fields of a context type into a
+ * sequence of instructions that access fields of the underlying structure:
+ *     struct __sk_buff    -> struct sk_buff
+ *     struct bpf_sock_ops -> struct sock
  */
-static int convert_ctx_accesses(struct bpf_verifier_env *env)
+static int convert_ctx_accesses(struct bpf_verifier_env *env,
+				bpf_convert_ctx_access_t convert_ctx_access,
+				enum bpf_reg_type ctx_type)
 {
 	const struct bpf_verifier_ops *ops = env->ops;
 	int i, cnt, size, ctx_field_size, delta = 0;
@@ -5218,12 +5275,14 @@ static int convert_ctx_accesses(struct bpf_verifier_env *env)
 		}
 	}
 
-	if (!ops->convert_ctx_access || bpf_prog_is_dev_bound(env->prog->aux))
+	if (!convert_ctx_access || bpf_prog_is_dev_bound(env->prog->aux))
 		return 0;
 
 	insn = env->prog->insnsi + delta;
 
 	for (i = 0; i < insn_cnt; i++, insn++) {
+		enum bpf_reg_type ptr_type;
+
 		if (insn->code == (BPF_LDX | BPF_MEM | BPF_B) ||
 		    insn->code == (BPF_LDX | BPF_MEM | BPF_H) ||
 		    insn->code == (BPF_LDX | BPF_MEM | BPF_W) ||
@@ -5237,7 +5296,8 @@ static int convert_ctx_accesses(struct bpf_verifier_env *env)
 		else
 			continue;
 
-		if (env->insn_aux_data[i + delta].ptr_type != PTR_TO_CTX)
+		ptr_type = env->insn_aux_data[i + delta].ptr_type;
+		if (ptr_type != ctx_type)
 			continue;
 
 		ctx_field_size = env->insn_aux_data[i + delta].ctx_field_size;
@@ -5269,8 +5329,8 @@ static int convert_ctx_accesses(struct bpf_verifier_env *env)
 		}
 
 		target_size = 0;
-		cnt = ops->convert_ctx_access(type, insn, insn_buf, env->prog,
-					      &target_size);
+		cnt = convert_ctx_access(type, insn, insn_buf, env->prog,
+					 &target_size);
 		if (cnt == 0 || cnt >= ARRAY_SIZE(insn_buf) ||
 		    (ctx_field_size && !target_size)) {
 			verbose(env, "bpf verifier is misconfigured\n");
@@ -5785,7 +5845,13 @@ int bpf_check(struct bpf_prog **prog, union bpf_attr *attr)
 
 	if (ret == 0)
 		/* program is valid, convert *(u32*)(ctx + off) accesses */
-		ret = convert_ctx_accesses(env);
+		ret = convert_ctx_accesses(env, env->ops->convert_ctx_access,
+					   PTR_TO_CTX);
+
+	if (ret == 0)
+		/* Convert *(u32*)(sock_ops + off) accesses */
+		ret = convert_ctx_accesses(env, bpf_sock_convert_ctx_access,
+					   PTR_TO_SOCKET);
 
 	if (ret == 0)
 		ret = fixup_bpf_calls(env);
diff --git a/net/core/filter.c b/net/core/filter.c
index 0baa715e4699..4c35152fb3a8 100644
--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -4496,23 +4496,29 @@ static bool __sock_filter_check_size(int off, int size,
 	return size == size_default;
 }
 
-static bool sock_filter_is_valid_access(int off, int size,
-					enum bpf_access_type type,
-					const struct bpf_prog *prog,
-					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)
 {
 	if (off < 0 || off >= sizeof(struct bpf_sock))
 		return false;
 	if (off % size != 0)
 		return false;
-	if (!__sock_filter_check_attach_type(off, type,
-					     prog->expected_attach_type))
-		return false;
 	if (!__sock_filter_check_size(off, size, info))
 		return false;
 	return true;
 }
 
+static bool sock_filter_is_valid_access(int off, int size,
+					enum bpf_access_type type,
+					const struct bpf_prog *prog,
+					struct bpf_insn_access_aux *info)
+{
+	if (!__sock_filter_check_attach_type(off, type,
+					     prog->expected_attach_type))
+		return false;
+	return bpf_sock_is_valid_access(off, size, type, info);
+}
+
 static int bpf_unclone_prologue(struct bpf_insn *insn_buf, bool direct_write,
 				const struct bpf_prog *prog, int drop_verdict)
 {
@@ -5153,10 +5159,10 @@ static u32 bpf_convert_ctx_access(enum bpf_access_type type,
 	return insn - insn_buf;
 }
 
-static u32 sock_filter_convert_ctx_access(enum bpf_access_type type,
-					  const struct bpf_insn *si,
-					  struct bpf_insn *insn_buf,
-					  struct bpf_prog *prog, u32 *target_size)
+u32 bpf_sock_convert_ctx_access(enum bpf_access_type type,
+				const struct bpf_insn *si,
+				struct bpf_insn *insn_buf,
+				struct bpf_prog *prog, u32 *target_size)
 {
 	struct bpf_insn *insn = insn_buf;
 	int off;
@@ -5926,7 +5932,7 @@ const struct bpf_prog_ops lwt_xmit_prog_ops = {
 const struct bpf_verifier_ops cg_sock_verifier_ops = {
 	.get_func_proto		= sock_filter_func_proto,
 	.is_valid_access	= sock_filter_is_valid_access,
-	.convert_ctx_access	= sock_filter_convert_ctx_access,
+	.convert_ctx_access	= bpf_sock_convert_ctx_access,
 };
 
 const struct bpf_prog_ops cg_sock_prog_ops = {
-- 
2.14.1

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