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@wand.net.nz>
Acked-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>

include/linux/bpf.h

@@ -154,6 +154,7 @@ 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 */
@@ -162,6 +163,7 @@ enum bpf_return_type {
 	RET_VOID,			/* function doesn't return anything */
 	RET_PTR_TO_MAP_VALUE,		/* returns a pointer to map elem value */
 	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
@@ -213,6 +215,8 @@ enum bpf_reg_type {
 	PTR_TO_PACKET,		 /* reg points to skb->data */
 	PTR_TO_PACKET_END,	 /* skb->data + headlen */
 	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 */
 };
 
 /* The information passed from prog-specific *_is_valid_access
@@ -343,6 +347,11 @@ 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);
@@ -836,4 +845,29 @@ extern const struct bpf_func_proto bpf_get_local_storage_proto;
 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_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);
+#else
+static inline bool bpf_sock_is_valid_access(int off, int size,
+					    enum bpf_access_type type,
+					    struct bpf_insn_access_aux *info)
+{
+	return false;
+}
+static inline 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)
+{
+	return 0;
+}
+#endif
+
 #endif /* _LINUX_BPF_H */

include/linux/bpf_verifier.h

@@ -58,6 +58,8 @@ 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;
 	/* For scalar types (SCALAR_VALUE), this represents our knowledge of

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.
@@ -267,6 +267,8 @@ static const char * const reg_type_str[] = {
 	[PTR_TO_PACKET_META]	= "pkt_meta",
 	[PTR_TO_PACKET_END]	= "pkt_end",
 	[PTR_TO_FLOW_KEYS]	= "flow_keys",
+	[PTR_TO_SOCKET]		= "sock",
+	[PTR_TO_SOCKET_OR_NULL] = "sock_or_null",
 };
 
 static char slot_type_char[] = {
@@ -973,6 +975,8 @@ static bool is_spillable_regtype(enum bpf_reg_type type)
 	case PTR_TO_PACKET_END:
 	case PTR_TO_FLOW_KEYS:
 	case CONST_PTR_TO_MAP:
+	case PTR_TO_SOCKET:
+	case PTR_TO_SOCKET_OR_NULL:
 		return true;
 	default:
 		return false;
@@ -1341,6 +1345,28 @@ static int check_flow_keys_access(struct bpf_verifier_env *env, int off,
 	return 0;
 }
 
+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 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)
 {
@@ -1459,6 +1485,9 @@ static int check_ptr_alignment(struct bpf_verifier_env *env,
 		 */
 		strict = true;
 		break;
+	case PTR_TO_SOCKET:
+		pointer_desc = "sock ";
+		break;
 	default:
 		break;
 	}
@@ -1726,6 +1755,14 @@ 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) {
+		if (t == BPF_WRITE) {
+			verbose(env, "cannot write into socket\n");
+			return -EACCES;
+		}
+		err = check_sock_access(env, regno, off, size, t);
+		if (!err && 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]);
@@ -1948,6 +1985,10 @@ 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_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
@@ -2543,6 +2584,10 @@ static int check_helper_call(struct bpf_verifier_env *env, int func_id, int insn
 		}
 		regs[BPF_REG_0].map_ptr = meta.map_ptr;
 		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;
+		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);
@@ -2680,6 +2725,8 @@ 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;
@@ -3627,6 +3674,8 @@ 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
@@ -4402,6 +4451,8 @@ static bool regsafe(struct bpf_reg_state *rold, struct bpf_reg_state *rcur,
 	case CONST_PTR_TO_MAP:
 	case PTR_TO_PACKET_END:
 	case PTR_TO_FLOW_KEYS:
+	case PTR_TO_SOCKET:
+	case PTR_TO_SOCKET_OR_NULL:
 		/* Only valid matches are exact, which memcmp() above
 		 * would have accepted
 		 */
@@ -4679,6 +4730,37 @@ static int is_state_visited(struct bpf_verifier_env *env, int insn_idx)
 	return 0;
 }
 
+/* Return true if it's OK to have the same insn return a different type. */
+static bool reg_type_mismatch_ok(enum bpf_reg_type type)
+{
+	switch (type) {
+	case PTR_TO_CTX:
+	case PTR_TO_SOCKET:
+	case PTR_TO_SOCKET_OR_NULL:
+		return false;
+	default:
+		return true;
+	}
+}
+
+/* If an instruction was previously used with particular pointer types, then we
+ * need to be careful to avoid cases such as the below, where it may be ok
+ * for one branch accessing the pointer, but not ok for the other branch:
+ *
+ * R1 = sock_ptr
+ * goto X;
+ * ...
+ * R1 = some_other_valid_ptr;
+ * goto X;
+ * ...
+ * R2 = *(u32 *)(R1 + 0);
+ */
+static bool reg_type_mismatch(enum bpf_reg_type src, enum bpf_reg_type prev)
+{
+	return src != prev && (!reg_type_mismatch_ok(src) ||
+			       !reg_type_mismatch_ok(prev));
+}
+
 static int do_check(struct bpf_verifier_env *env)
 {
 	struct bpf_verifier_state *state;
@@ -4811,9 +4893,7 @@ static int do_check(struct bpf_verifier_env *env)
 				 */
 				*prev_src_type = src_reg_type;
 
-			} else if (src_reg_type != *prev_src_type &&
-				   (src_reg_type == PTR_TO_CTX ||
-				    *prev_src_type == PTR_TO_CTX)) {
+			} else if (reg_type_mismatch(src_reg_type, *prev_src_type)) {
 				/* ABuser program is trying to use the same insn
 				 * dst_reg = *(u32*) (src_reg + off)
 				 * with different pointer types:
@@ -4858,9 +4938,7 @@ static int do_check(struct bpf_verifier_env *env)
 
 			if (*prev_dst_type == NOT_INIT) {
 				*prev_dst_type = dst_reg_type;
-			} else if (dst_reg_type != *prev_dst_type &&
-				   (dst_reg_type == PTR_TO_CTX ||
-				    *prev_dst_type == PTR_TO_CTX)) {
+			} else if (reg_type_mismatch(dst_reg_type, *prev_dst_type)) {
 				verbose(env, "same insn cannot be used with different pointers\n");
 				return -EINVAL;
 			}
@@ -5286,8 +5364,10 @@ 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)
 {
@@ -5316,12 +5396,14 @@ static int convert_ctx_accesses(struct bpf_verifier_env *env)
 		}
 	}
 
-	if (!ops->convert_ctx_access || bpf_prog_is_dev_bound(env->prog->aux))
+	if (bpf_prog_is_dev_bound(env->prog->aux))
 		return 0;
 
 	insn = env->prog->insnsi + delta;
 
 	for (i = 0; i < insn_cnt; i++, insn++) {
+		bpf_convert_ctx_access_t convert_ctx_access;
+
 		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) ||
@@ -5363,8 +5445,18 @@ static int convert_ctx_accesses(struct bpf_verifier_env *env)
 			continue;
 		}
 
-		if (env->insn_aux_data[i + delta].ptr_type != PTR_TO_CTX)
+		switch (env->insn_aux_data[i + delta].ptr_type) {
+		case PTR_TO_CTX:
+			if (!ops->convert_ctx_access)
+				continue;
+			convert_ctx_access = ops->convert_ctx_access;
+			break;
+		case PTR_TO_SOCKET:
+			convert_ctx_access = bpf_sock_convert_ctx_access;
+			break;
+		default:
 			continue;
+		}
 
 		ctx_field_size = env->insn_aux_data[i + delta].ctx_field_size;
 		size = BPF_LDST_BYTES(insn);
@@ -5396,8 +5488,8 @@ 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");

net/core/filter.c

@@ -5394,23 +5394,29 @@ 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 (!bpf_sock_is_valid_access(off, size, type, info))
+		return false;
+	return __sock_filter_check_attach_type(off, type,
+					       prog->expected_attach_type);
+}
+
 static int bpf_unclone_prologue(struct bpf_insn *insn_buf, bool direct_write,
 				const struct bpf_prog *prog, int drop_verdict)
 {
@@ -6122,10 +6128,10 @@ 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;
@@ -7037,7 +7043,7 @@ const struct bpf_prog_ops lwt_seg6local_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 = {