Merge branch 'bpf-sk-lookup'

Joe Stringer says:

====================
This series proposes a new helper for the BPF API which allows BPF programs to
perform lookups for sockets in a network namespace. This would allow programs
to determine early on in processing whether the stack is expecting to receive
the packet, and perform some action (eg drop, forward somewhere) based on this
information.

The series is structured roughly into:
* Misc refactor
* Add the socket pointer type
* Add reference tracking to ensure that socket references are freed
* Extend the BPF API to add sk_lookup_xxx() / sk_release() functions
* Add tests/documentation

The helper proposed in this series includes a parameter for a tuple which must
be filled in by the caller to determine the socket to look up. The simplest
case would be filling with the contents of the packet, ie mapping the packet's
5-tuple into the parameter. In common cases, it may alternatively be useful to
reverse the direction of the tuple and perform a lookup, to find the socket
that initiates this connection; and if the BPF program ever performs a form of
IP address translation, it may further be useful to be able to look up
arbitrary tuples that are not based upon the packet, but instead based on state
held in BPF maps or hardcoded in the BPF program.

Currently, access into the socket's fields are limited to those which are
otherwise already accessible, and are restricted to read-only access.

Changes since v3:
* New patch: "bpf: Reuse canonical string formatter for ctx errs"
* Add PTR_TO_SOCKET to is_ctx_reg().
* Add a few new checks to prevent mixing of socket/non-socket pointers.
* Swap order of checks in sock_filter_is_valid_access().
* Prefix register spill macros with "bpf_".
* Add acks from previous round
* Rebase

Changes since v2:
* New patch: "selftests/bpf: Generalize dummy program types".
  This enables adding verifier tests for socket lookup with tail calls.
* Define the semantics of the new helpers more clearly in uAPI header.
* Fix release of caller_net when netns is not specified.
* Use skb->sk to find caller net when skb->dev is unavailable.
* Fix build with !CONFIG_NET.
* Replace ptr_id defensive coding when releasing reference state with an
  internal error (-EFAULT).
* Remove flags argument to sk_release().
* Add several new assembly tests suggested by Daniel.
* Add a few new C tests.
* Fix typo in verifier error message.

Changes since v1:
* Limit netns_id field to 32 bits
* Reuse reg_type_mismatch() in more places
* Reduce the number of passes at convert_ctx_access()
* Replace ptr_id defensive coding when releasing reference state with an
  internal error (-EFAULT)
* Rework 'struct bpf_sock_tuple' to allow passing a packet pointer
* Allow direct packet access from helper
* Fix compile error with CONFIG_IPV6 enabled
* Improve commit messages

Changes since RFC:
* Split up sk_lookup() into sk_lookup_tcp(), sk_lookup_udp().
* Only take references on the socket when necessary.
  * Make sk_release() only free the socket reference in this case.
* Fix some runtime reference leaks:
  * Disallow BPF_LD_[ABS|IND] instructions while holding a reference.
  * Disallow bpf_tail_call() while holding a reference.
* Prevent the same instruction being used for reference and other
  pointer type.
* Simplify locating copies of a reference during helper calls by caching
  the pointer id from the caller.
* Fix kbuild compilation warnings with particular configs.
* Improve code comments describing the new verifier pieces.
* Tested by Nitin
====================
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>

Documentation/networking/filter.txt

@@ -1125,6 +1125,14 @@ pointer type.  The types of pointers describe their base, as follows:
     PTR_TO_STACK        Frame pointer.
     PTR_TO_PACKET       skb->data.
     PTR_TO_PACKET_END   skb->data + headlen; arithmetic forbidden.
+    PTR_TO_SOCKET       Pointer to struct bpf_sock_ops, implicitly refcounted.
+    PTR_TO_SOCKET_OR_NULL
+                        Either a pointer to a socket, or NULL; socket lookup
+                        returns this type, which becomes a PTR_TO_SOCKET when
+                        checked != NULL. PTR_TO_SOCKET is reference-counted,
+                        so programs must release the reference through the
+                        socket release function before the end of the program.
+                        Arithmetic on these pointers is forbidden.
 However, a pointer may be offset from this base (as a result of pointer
 arithmetic), and this is tracked in two parts: the 'fixed offset' and 'variable
 offset'.  The former is used when an exactly-known value (e.g. an immediate
@@ -1171,6 +1179,13 @@ over the Ethernet header, then reads IHL and addes (IHL * 4), the resulting
 pointer will have a variable offset known to be 4n+2 for some n, so adding the 2
 bytes (NET_IP_ALIGN) gives a 4-byte alignment and so word-sized accesses through
 that pointer are safe.
+The 'id' field is also used on PTR_TO_SOCKET and PTR_TO_SOCKET_OR_NULL, common
+to all copies of the pointer returned from a socket lookup. This has similar
+behaviour to the handling for PTR_TO_MAP_VALUE_OR_NULL->PTR_TO_MAP_VALUE, but
+it also handles reference tracking for the pointer. PTR_TO_SOCKET implicitly
+represents a reference to the corresponding 'struct sock'. To ensure that the
+reference is not leaked, it is imperative to NULL-check the reference and in
+the non-NULL case, and pass the valid reference to the socket release function.
 
 Direct packet access
 --------------------
@@ -1444,6 +1459,55 @@ Error:
   8: (7a) *(u64 *)(r0 +0) = 1
   R0 invalid mem access 'imm'
 
+Program that performs a socket lookup then sets the pointer to NULL without
+checking it:
+value:
+  BPF_MOV64_IMM(BPF_REG_2, 0),
+  BPF_STX_MEM(BPF_W, BPF_REG_10, BPF_REG_2, -8),
+  BPF_MOV64_REG(BPF_REG_2, BPF_REG_10),
+  BPF_ALU64_IMM(BPF_ADD, BPF_REG_2, -8),
+  BPF_MOV64_IMM(BPF_REG_3, 4),
+  BPF_MOV64_IMM(BPF_REG_4, 0),
+  BPF_MOV64_IMM(BPF_REG_5, 0),
+  BPF_EMIT_CALL(BPF_FUNC_sk_lookup_tcp),
+  BPF_MOV64_IMM(BPF_REG_0, 0),
+  BPF_EXIT_INSN(),
+Error:
+  0: (b7) r2 = 0
+  1: (63) *(u32 *)(r10 -8) = r2
+  2: (bf) r2 = r10
+  3: (07) r2 += -8
+  4: (b7) r3 = 4
+  5: (b7) r4 = 0
+  6: (b7) r5 = 0
+  7: (85) call bpf_sk_lookup_tcp#65
+  8: (b7) r0 = 0
+  9: (95) exit
+  Unreleased reference id=1, alloc_insn=7
+
+Program that performs a socket lookup but does not NULL-check the returned
+value:
+  BPF_MOV64_IMM(BPF_REG_2, 0),
+  BPF_STX_MEM(BPF_W, BPF_REG_10, BPF_REG_2, -8),
+  BPF_MOV64_REG(BPF_REG_2, BPF_REG_10),
+  BPF_ALU64_IMM(BPF_ADD, BPF_REG_2, -8),
+  BPF_MOV64_IMM(BPF_REG_3, 4),
+  BPF_MOV64_IMM(BPF_REG_4, 0),
+  BPF_MOV64_IMM(BPF_REG_5, 0),
+  BPF_EMIT_CALL(BPF_FUNC_sk_lookup_tcp),
+  BPF_EXIT_INSN(),
+Error:
+  0: (b7) r2 = 0
+  1: (63) *(u32 *)(r10 -8) = r2
+  2: (bf) r2 = r10
+  3: (07) r2 += -8
+  4: (b7) r3 = 4
+  5: (b7) r4 = 0
+  6: (b7) r5 = 0
+  7: (85) call bpf_sk_lookup_tcp#65
+  8: (95) exit
+  Unreleased reference id=1, alloc_insn=7
+
 Testing
 -------
 

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
@@ -102,6 +104,17 @@ struct bpf_stack_state {
 	u8 slot_type[BPF_REG_SIZE];
 };
 
+struct bpf_reference_state {
+	/* Track each reference created with a unique id, even if the same
+	 * instruction creates the reference multiple times (eg, via CALL).
+	 */
+	int id;
+	/* Instruction where the allocation of this reference occurred. This
+	 * is used purely to inform the user of a reference leak.
+	 */
+	int insn_idx;
+};
+
 /* state of the program:
  * type of all registers and stack info
  */
@@ -119,7 +132,9 @@ struct bpf_func_state {
 	 */
 	u32 subprogno;
 
-	/* should be second to last. See copy_func_state() */
+	/* The following fields should be last. See copy_func_state() */
+	int acquired_refs;
+	struct bpf_reference_state *refs;
 	int allocated_stack;
 	struct bpf_stack_state *stack;
 };
@@ -131,6 +146,17 @@ struct bpf_verifier_state {
 	u32 curframe;
 };
 
+#define bpf_get_spilled_reg(slot, frame)				\
+	(((slot < frame->allocated_stack / BPF_REG_SIZE) &&		\
+	  (frame->stack[slot].slot_type[0] == STACK_SPILL))		\
+	 ? &frame->stack[slot].spilled_ptr : NULL)
+
+/* Iterate over 'frame', setting 'reg' to either NULL or a spilled register. */
+#define bpf_for_each_spilled_reg(iter, frame, reg)			\
+	for (iter = 0, reg = bpf_get_spilled_reg(iter, frame);		\
+	     iter < frame->allocated_stack / BPF_REG_SIZE;		\
+	     iter++, reg = bpf_get_spilled_reg(iter, frame))
+
 /* linked list of verifier states used to prune search */
 struct bpf_verifier_state_list {
 	struct bpf_verifier_state state;
@@ -204,11 +230,16 @@ __printf(2, 0) void bpf_verifier_vlog(struct bpf_verifier_log *log,
 __printf(2, 3) void bpf_verifier_log_write(struct bpf_verifier_env *env,
 					   const char *fmt, ...);
 
-static inline struct bpf_reg_state *cur_regs(struct bpf_verifier_env *env)
+static inline struct bpf_func_state *cur_func(struct bpf_verifier_env *env)
 {
 	struct bpf_verifier_state *cur = env->cur_state;
 
-	return cur->frame[cur->curframe]->regs;
+	return cur->frame[cur->curframe];
+}
+
+static inline struct bpf_reg_state *cur_regs(struct bpf_verifier_env *env)
+{
+	return cur_func(env)->regs;
 }
 
 int bpf_prog_offload_verifier_prep(struct bpf_verifier_env *env);

include/uapi/linux/bpf.h

@@ -2144,6 +2144,77 @@ union bpf_attr {
  *		request in the skb.
  *	Return
  *		0 on success, or a negative error in case of failure.
+ *
+ * struct bpf_sock *bpf_sk_lookup_tcp(void *ctx, struct bpf_sock_tuple *tuple, u32 tuple_size, u32 netns, u64 flags)
+ *	Description
+ *		Look for TCP socket matching *tuple*, optionally in a child
+ *		network namespace *netns*. The return value must be checked,
+ *		and if non-NULL, released via **bpf_sk_release**\ ().
+ *
+ *		The *ctx* should point to the context of the program, such as
+ *		the skb or socket (depending on the hook in use). This is used
+ *		to determine the base network namespace for the lookup.
+ *
+ *		*tuple_size* must be one of:
+ *
+ *		**sizeof**\ (*tuple*\ **->ipv4**)
+ *			Look for an IPv4 socket.
+ *		**sizeof**\ (*tuple*\ **->ipv6**)
+ *			Look for an IPv6 socket.
+ *
+ *		If the *netns* is zero, then the socket lookup table in the
+ *		netns associated with the *ctx* will be used. For the TC hooks,
+ *		this in the netns of the device in the skb. For socket hooks,
+ *		this in the netns of the socket. If *netns* is non-zero, then
+ *		it specifies the ID of the netns relative to the netns
+ *		associated with the *ctx*.
+ *
+ *		All values for *flags* are reserved for future usage, and must
+ *		be left at zero.
+ *
+ *		This helper is available only if the kernel was compiled with
+ *		**CONFIG_NET** configuration option.
+ *	Return
+ *		Pointer to *struct bpf_sock*, or NULL in case of failure.
+ *
+ * struct bpf_sock *bpf_sk_lookup_udp(void *ctx, struct bpf_sock_tuple *tuple, u32 tuple_size, u32 netns, u64 flags)
+ *	Description
+ *		Look for UDP socket matching *tuple*, optionally in a child
+ *		network namespace *netns*. The return value must be checked,
+ *		and if non-NULL, released via **bpf_sk_release**\ ().
+ *
+ *		The *ctx* should point to the context of the program, such as
+ *		the skb or socket (depending on the hook in use). This is used
+ *		to determine the base network namespace for the lookup.
+ *
+ *		*tuple_size* must be one of:
+ *
+ *		**sizeof**\ (*tuple*\ **->ipv4**)
+ *			Look for an IPv4 socket.
+ *		**sizeof**\ (*tuple*\ **->ipv6**)
+ *			Look for an IPv6 socket.
+ *
+ *		If the *netns* is zero, then the socket lookup table in the
+ *		netns associated with the *ctx* will be used. For the TC hooks,
+ *		this in the netns of the device in the skb. For socket hooks,
+ *		this in the netns of the socket. If *netns* is non-zero, then
+ *		it specifies the ID of the netns relative to the netns
+ *		associated with the *ctx*.
+ *
+ *		All values for *flags* are reserved for future usage, and must
+ *		be left at zero.
+ *
+ *		This helper is available only if the kernel was compiled with
+ *		**CONFIG_NET** configuration option.
+ *	Return
+ *		Pointer to *struct bpf_sock*, or NULL in case of failure.
+ *
+ * int bpf_sk_release(struct bpf_sock *sk)
+ *	Description
+ *		Release the reference held by *sock*. *sock* must be a non-NULL
+ *		pointer that was returned from bpf_sk_lookup_xxx\ ().
+ *	Return
+ *		0 on success, or a negative error in case of failure.
  */
 #define __BPF_FUNC_MAPPER(FN)		\
 	FN(unspec),			\
@@ -2229,7 +2300,10 @@ union bpf_attr {
 	FN(get_current_cgroup_id),	\
 	FN(get_local_storage),		\
 	FN(sk_select_reuseport),	\
-	FN(skb_ancestor_cgroup_id),
+	FN(skb_ancestor_cgroup_id),	\
+	FN(sk_lookup_tcp),		\
+	FN(sk_lookup_udp),		\
+	FN(sk_release),
 
 /* integer value in 'imm' field of BPF_CALL instruction selects which helper
  * function eBPF program intends to call
@@ -2399,6 +2473,23 @@ struct bpf_sock {
 				 */
 };
 
+struct bpf_sock_tuple {
+	union {
+		struct {
+			__be32 saddr;
+			__be32 daddr;
+			__be16 sport;
+			__be16 dport;
+		} ipv4;
+		struct {
+			__be32 saddr[4];
+			__be32 daddr[4];
+			__be16 sport;
+			__be16 dport;
+		} ipv6;
+	};
+};
+
 #define XDP_PACKET_HEADROOM 256
 
 /* User return codes for XDP prog type.

net/core/filter.c

@@ -58,13 +58,17 @@
 #include <net/busy_poll.h>
 #include <net/tcp.h>
 #include <net/xfrm.h>
+#include <net/udp.h>
 #include <linux/bpf_trace.h>
 #include <net/xdp_sock.h>
 #include <linux/inetdevice.h>
+#include <net/inet_hashtables.h>
+#include <net/inet6_hashtables.h>
 #include <net/ip_fib.h>
 #include <net/flow.h>
 #include <net/arp.h>
 #include <net/ipv6.h>
+#include <net/net_namespace.h>
 #include <linux/seg6_local.h>
 #include <net/seg6.h>
 #include <net/seg6_local.h>
@@ -4813,6 +4817,141 @@ static const struct bpf_func_proto bpf_lwt_seg6_adjust_srh_proto = {
 };
 #endif /* CONFIG_IPV6_SEG6_BPF */
 
+struct sock *sk_lookup(struct net *net, struct bpf_sock_tuple *tuple,
+		       struct sk_buff *skb, u8 family, u8 proto)
+{
+	int dif = skb->dev->ifindex;
+	bool refcounted = false;
+	struct sock *sk = NULL;
+
+	if (family == AF_INET) {
+		__be32 src4 = tuple->ipv4.saddr;
+		__be32 dst4 = tuple->ipv4.daddr;
+		int sdif = inet_sdif(skb);
+
+		if (proto == IPPROTO_TCP)
+			sk = __inet_lookup(net, &tcp_hashinfo, skb, 0,
+					   src4, tuple->ipv4.sport,
+					   dst4, tuple->ipv4.dport,
+					   dif, sdif, &refcounted);
+		else
+			sk = __udp4_lib_lookup(net, src4, tuple->ipv4.sport,
+					       dst4, tuple->ipv4.dport,
+					       dif, sdif, &udp_table, skb);
+#if IS_ENABLED(CONFIG_IPV6)
+	} else {
+		struct in6_addr *src6 = (struct in6_addr *)&tuple->ipv6.saddr;
+		struct in6_addr *dst6 = (struct in6_addr *)&tuple->ipv6.daddr;
+		int sdif = inet6_sdif(skb);
+
+		if (proto == IPPROTO_TCP)
+			sk = __inet6_lookup(net, &tcp_hashinfo, skb, 0,
+					    src6, tuple->ipv6.sport,
+					    dst6, tuple->ipv6.dport,
+					    dif, sdif, &refcounted);
+		else
+			sk = __udp6_lib_lookup(net, src6, tuple->ipv6.sport,
+					       dst6, tuple->ipv6.dport,
+					       dif, sdif, &udp_table, skb);
+#endif
+	}
+
+	if (unlikely(sk && !refcounted && !sock_flag(sk, SOCK_RCU_FREE))) {
+		WARN_ONCE(1, "Found non-RCU, unreferenced socket!");
+		sk = NULL;
+	}
+	return sk;
+}
+
+/* bpf_sk_lookup performs the core lookup for different types of sockets,
+ * taking a reference on the socket if it doesn't have the flag SOCK_RCU_FREE.
+ * Returns the socket as an 'unsigned long' to simplify the casting in the
+ * callers to satisfy BPF_CALL declarations.
+ */
+static unsigned long
+bpf_sk_lookup(struct sk_buff *skb, struct bpf_sock_tuple *tuple, u32 len,
+	      u8 proto, u64 netns_id, u64 flags)
+{
+	struct net *caller_net;
+	struct sock *sk = NULL;
+	u8 family = AF_UNSPEC;
+	struct net *net;
+
+	family = len == sizeof(tuple->ipv4) ? AF_INET : AF_INET6;
+	if (unlikely(family == AF_UNSPEC || netns_id > U32_MAX || flags))
+		goto out;
+
+	if (skb->dev)
+		caller_net = dev_net(skb->dev);
+	else
+		caller_net = sock_net(skb->sk);
+	if (netns_id) {
+		net = get_net_ns_by_id(caller_net, netns_id);
+		if (unlikely(!net))
+			goto out;
+		sk = sk_lookup(net, tuple, skb, family, proto);
+		put_net(net);
+	} else {
+		net = caller_net;
+		sk = sk_lookup(net, tuple, skb, family, proto);
+	}
+
+	if (sk)
+		sk = sk_to_full_sk(sk);
+out:
+	return (unsigned long) sk;
+}
+
+BPF_CALL_5(bpf_sk_lookup_tcp, struct sk_buff *, skb,
+	   struct bpf_sock_tuple *, tuple, u32, len, u64, netns_id, u64, flags)
+{
+	return bpf_sk_lookup(skb, tuple, len, IPPROTO_TCP, netns_id, flags);
+}
+
+static const struct bpf_func_proto bpf_sk_lookup_tcp_proto = {
+	.func		= bpf_sk_lookup_tcp,
+	.gpl_only	= false,
+	.pkt_access	= true,
+	.ret_type	= RET_PTR_TO_SOCKET_OR_NULL,
+	.arg1_type	= ARG_PTR_TO_CTX,
+	.arg2_type	= ARG_PTR_TO_MEM,
+	.arg3_type	= ARG_CONST_SIZE,
+	.arg4_type	= ARG_ANYTHING,
+	.arg5_type	= ARG_ANYTHING,
+};
+
+BPF_CALL_5(bpf_sk_lookup_udp, struct sk_buff *, skb,
+	   struct bpf_sock_tuple *, tuple, u32, len, u64, netns_id, u64, flags)
+{
+	return bpf_sk_lookup(skb, tuple, len, IPPROTO_UDP, netns_id, flags);
+}
+
+static const struct bpf_func_proto bpf_sk_lookup_udp_proto = {
+	.func		= bpf_sk_lookup_udp,
+	.gpl_only	= false,
+	.pkt_access	= true,
+	.ret_type	= RET_PTR_TO_SOCKET_OR_NULL,
+	.arg1_type	= ARG_PTR_TO_CTX,
+	.arg2_type	= ARG_PTR_TO_MEM,
+	.arg3_type	= ARG_CONST_SIZE,
+	.arg4_type	= ARG_ANYTHING,
+	.arg5_type	= ARG_ANYTHING,
+};
+
+BPF_CALL_1(bpf_sk_release, struct sock *, sk)
+{
+	if (!sock_flag(sk, SOCK_RCU_FREE))
+		sock_gen_put(sk);
+	return 0;
+}
+
+static const struct bpf_func_proto bpf_sk_release_proto = {
+	.func		= bpf_sk_release,
+	.gpl_only	= false,
+	.ret_type	= RET_INTEGER,
+	.arg1_type	= ARG_PTR_TO_SOCKET,
+};
+
 bool bpf_helper_changes_pkt_data(void *func)
 {
 	if (func == bpf_skb_vlan_push ||
@@ -5019,6 +5158,12 @@ tc_cls_act_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog)
 	case BPF_FUNC_skb_ancestor_cgroup_id:
 		return &bpf_skb_ancestor_cgroup_id_proto;
 #endif
+	case BPF_FUNC_sk_lookup_tcp:
+		return &bpf_sk_lookup_tcp_proto;
+	case BPF_FUNC_sk_lookup_udp:
+		return &bpf_sk_lookup_udp_proto;
+	case BPF_FUNC_sk_release:
+		return &bpf_sk_release_proto;
 	default:
 		return bpf_base_func_proto(func_id);
 	}
@@ -5119,6 +5264,12 @@ sk_skb_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog)
 		return &bpf_sk_redirect_hash_proto;
 	case BPF_FUNC_get_local_storage:
 		return &bpf_get_local_storage_proto;
+	case BPF_FUNC_sk_lookup_tcp:
+		return &bpf_sk_lookup_tcp_proto;
+	case BPF_FUNC_sk_lookup_udp:
+		return &bpf_sk_lookup_udp_proto;
+	case BPF_FUNC_sk_release:
+		return &bpf_sk_release_proto;
 	default:
 		return bpf_base_func_proto(func_id);
 	}
@@ -5394,23 +5545,29 @@ 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 +6279,10 @@ 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 +7194,7 @@ 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 = {

tools/include/uapi/linux/bpf.h

@@ -2144,6 +2144,77 @@ union bpf_attr {
  *		request in the skb.
  *	Return
  *		0 on success, or a negative error in case of failure.
+ *
+ * struct bpf_sock *bpf_sk_lookup_tcp(void *ctx, struct bpf_sock_tuple *tuple, u32 tuple_size, u32 netns, u64 flags)
+ *	Description
+ *		Look for TCP socket matching *tuple*, optionally in a child
+ *		network namespace *netns*. The return value must be checked,
+ *		and if non-NULL, released via **bpf_sk_release**\ ().
+ *
+ *		The *ctx* should point to the context of the program, such as
+ *		the skb or socket (depending on the hook in use). This is used
+ *		to determine the base network namespace for the lookup.
+ *
+ *		*tuple_size* must be one of:
+ *
+ *		**sizeof**\ (*tuple*\ **->ipv4**)
+ *			Look for an IPv4 socket.
+ *		**sizeof**\ (*tuple*\ **->ipv6**)
+ *			Look for an IPv6 socket.
+ *
+ *		If the *netns* is zero, then the socket lookup table in the
+ *		netns associated with the *ctx* will be used. For the TC hooks,
+ *		this in the netns of the device in the skb. For socket hooks,
+ *		this in the netns of the socket. If *netns* is non-zero, then
+ *		it specifies the ID of the netns relative to the netns
+ *		associated with the *ctx*.
+ *
+ *		All values for *flags* are reserved for future usage, and must
+ *		be left at zero.
+ *
+ *		This helper is available only if the kernel was compiled with
+ *		**CONFIG_NET** configuration option.
+ *	Return
+ *		Pointer to *struct bpf_sock*, or NULL in case of failure.
+ *
+ * struct bpf_sock *bpf_sk_lookup_udp(void *ctx, struct bpf_sock_tuple *tuple, u32 tuple_size, u32 netns, u64 flags)
+ *	Description
+ *		Look for UDP socket matching *tuple*, optionally in a child
+ *		network namespace *netns*. The return value must be checked,
+ *		and if non-NULL, released via **bpf_sk_release**\ ().
+ *
+ *		The *ctx* should point to the context of the program, such as
+ *		the skb or socket (depending on the hook in use). This is used
+ *		to determine the base network namespace for the lookup.
+ *
+ *		*tuple_size* must be one of:
+ *
+ *		**sizeof**\ (*tuple*\ **->ipv4**)
+ *			Look for an IPv4 socket.
+ *		**sizeof**\ (*tuple*\ **->ipv6**)
+ *			Look for an IPv6 socket.
+ *
+ *		If the *netns* is zero, then the socket lookup table in the
+ *		netns associated with the *ctx* will be used. For the TC hooks,
+ *		this in the netns of the device in the skb. For socket hooks,
+ *		this in the netns of the socket. If *netns* is non-zero, then
+ *		it specifies the ID of the netns relative to the netns
+ *		associated with the *ctx*.
+ *
+ *		All values for *flags* are reserved for future usage, and must
+ *		be left at zero.
+ *
+ *		This helper is available only if the kernel was compiled with
+ *		**CONFIG_NET** configuration option.
+ *	Return
+ *		Pointer to *struct bpf_sock*, or NULL in case of failure.
+ *
+ * int bpf_sk_release(struct bpf_sock *sk)
+ *	Description
+ *		Release the reference held by *sock*. *sock* must be a non-NULL
+ *		pointer that was returned from bpf_sk_lookup_xxx\ ().
+ *	Return
+ *		0 on success, or a negative error in case of failure.
  */
 #define __BPF_FUNC_MAPPER(FN)		\
 	FN(unspec),			\
@@ -2229,7 +2300,10 @@ union bpf_attr {
 	FN(get_current_cgroup_id),	\
 	FN(get_local_storage),		\
 	FN(sk_select_reuseport),	\
-	FN(skb_ancestor_cgroup_id),
+	FN(skb_ancestor_cgroup_id),	\
+	FN(sk_lookup_tcp),		\
+	FN(sk_lookup_udp),		\
+	FN(sk_release),
 
 /* integer value in 'imm' field of BPF_CALL instruction selects which helper
  * function eBPF program intends to call
@@ -2399,6 +2473,23 @@ struct bpf_sock {
 				 */
 };
 
+struct bpf_sock_tuple {
+	union {
+		struct {
+			__be32 saddr;
+			__be32 daddr;
+			__be16 sport;
+			__be16 dport;
+		} ipv4;
+		struct {
+			__be32 saddr[4];
+			__be32 daddr[4];
+			__be16 sport;
+			__be16 dport;
+		} ipv6;
+	};
+};
+
 #define XDP_PACKET_HEADROOM 256
 
 /* User return codes for XDP prog type.

tools/lib/bpf/libbpf.c

@@ -228,7 +228,7 @@ struct bpf_object {
 };
 #define obj_elf_valid(o)	((o)->efile.elf)
 
-static void bpf_program__unload(struct bpf_program *prog)
+void bpf_program__unload(struct bpf_program *prog)
 {
 	int i;
 
@@ -1375,7 +1375,7 @@ load_program(enum bpf_prog_type type, enum bpf_attach_type expected_attach_type,
 	return ret;
 }
 
-static int
+int
 bpf_program__load(struct bpf_program *prog,
 		  char *license, u32 kern_version)
 {

tools/lib/bpf/libbpf.h

@@ -128,10 +128,13 @@ void bpf_program__set_ifindex(struct bpf_program *prog, __u32 ifindex);
 
 const char *bpf_program__title(struct bpf_program *prog, bool needs_copy);
 
+int bpf_program__load(struct bpf_program *prog, char *license,
+		      u32 kern_version);
 int bpf_program__fd(struct bpf_program *prog);
 int bpf_program__pin_instance(struct bpf_program *prog, const char *path,
 			      int instance);
 int bpf_program__pin(struct bpf_program *prog, const char *path);
+void bpf_program__unload(struct bpf_program *prog);
 
 struct bpf_insn;
 

tools/testing/selftests/bpf/Makefile

@@ -36,7 +36,7 @@ TEST_GEN_FILES = test_pkt_access.o test_xdp.o test_l4lb.o test_tcp_estats.o test
 	test_get_stack_rawtp.o test_sockmap_kern.o test_sockhash_kern.o \
 	test_lwt_seg6local.o sendmsg4_prog.o sendmsg6_prog.o test_lirc_mode2_kern.o \
 	get_cgroup_id_kern.o socket_cookie_prog.o test_select_reuseport_kern.o \
-	test_skb_cgroup_id_kern.o bpf_flow.o netcnt_prog.o
+	test_skb_cgroup_id_kern.o bpf_flow.o netcnt_prog.o test_sk_lookup_kern.o
 
 # Order correspond to 'make run_tests' order
 TEST_PROGS := test_kmod.sh \

tools/testing/selftests/bpf/bpf_helpers.h

@@ -143,6 +143,18 @@ static unsigned long long (*bpf_skb_cgroup_id)(void *ctx) =
 	(void *) BPF_FUNC_skb_cgroup_id;
 static unsigned long long (*bpf_skb_ancestor_cgroup_id)(void *ctx, int level) =
 	(void *) BPF_FUNC_skb_ancestor_cgroup_id;
+static struct bpf_sock *(*bpf_sk_lookup_tcp)(void *ctx,
+					     struct bpf_sock_tuple *tuple,
+					     int size, unsigned int netns_id,
+					     unsigned long long flags) =
+	(void *) BPF_FUNC_sk_lookup_tcp;
+static struct bpf_sock *(*bpf_sk_lookup_udp)(void *ctx,
+					     struct bpf_sock_tuple *tuple,
+					     int size, unsigned int netns_id,
+					     unsigned long long flags) =
+	(void *) BPF_FUNC_sk_lookup_udp;
+static int (*bpf_sk_release)(struct bpf_sock *sk) =
+	(void *) BPF_FUNC_sk_release;
 
 /* llvm builtin functions that eBPF C program may use to
  * emit BPF_LD_ABS and BPF_LD_IND instructions

tools/testing/selftests/bpf/test_progs.c

@@ -1698,6 +1698,43 @@ static void test_task_fd_query_tp(void)
 				   "sys_enter_read");
 }
 
+static void test_reference_tracking()
+{
+	const char *file = "./test_sk_lookup_kern.o";
+	struct bpf_object *obj;
+	struct bpf_program *prog;
+	__u32 duration;
+	int err = 0;
+
+	obj = bpf_object__open(file);
+	if (IS_ERR(obj)) {
+		error_cnt++;
+		return;
+	}
+
+	bpf_object__for_each_program(prog, obj) {
+		const char *title;
+
+		/* Ignore .text sections */
+		title = bpf_program__title(prog, false);
+		if (strstr(title, ".text") != NULL)
+			continue;
+
+		bpf_program__set_type(prog, BPF_PROG_TYPE_SCHED_CLS);
+
+		/* Expect verifier failure if test name has 'fail' */
+		if (strstr(title, "fail") != NULL) {
+			libbpf_set_print(NULL, NULL, NULL);
+			err = !bpf_program__load(prog, "GPL", 0);
+			libbpf_set_print(printf, printf, NULL);
+		} else {
+			err = bpf_program__load(prog, "GPL", 0);
+		}
+		CHECK(err, title, "\n");
+	}
+	bpf_object__close(obj);
+}
+
 int main(void)
 {
 	jit_enabled = is_jit_enabled();
@@ -1719,6 +1756,7 @@ int main(void)
 	test_get_stack_raw_tp();
 	test_task_fd_query_rawtp();
 	test_task_fd_query_tp();
+	test_reference_tracking();
 
 	printf("Summary: %d PASSED, %d FAILED\n", pass_cnt, error_cnt);
 	return error_cnt ? EXIT_FAILURE : EXIT_SUCCESS;

tools/testing/selftests/bpf/test_sk_lookup_kern.c

+/* SPDX-License-Identifier: GPL-2.0 */
+// Copyright (c) 2018 Covalent IO, Inc. http://covalent.io
+
+#include <stddef.h>
+#include <stdbool.h>
+#include <string.h>
+#include <linux/bpf.h>
+#include <linux/if_ether.h>
+#include <linux/in.h>
+#include <linux/ip.h>
+#include <linux/ipv6.h>
+#include <linux/pkt_cls.h>
+#include <linux/tcp.h>
+#include <sys/socket.h>
+#include "bpf_helpers.h"
+#include "bpf_endian.h"
+
+int _version SEC("version") = 1;
+char _license[] SEC("license") = "GPL";
+
+/* Fill 'tuple' with L3 info, and attempt to find L4. On fail, return NULL. */
+static struct bpf_sock_tuple *get_tuple(void *data, __u64 nh_off,
+					void *data_end, __u16 eth_proto,
+					bool *ipv4)
+{
+	struct bpf_sock_tuple *result;
+	__u8 proto = 0;
+	__u64 ihl_len;
+
+	if (eth_proto == bpf_htons(ETH_P_IP)) {
+		struct iphdr *iph = (struct iphdr *)(data + nh_off);
+
+		if (iph + 1 > data_end)
+			return NULL;
+		ihl_len = iph->ihl * 4;
+		proto = iph->protocol;
+		*ipv4 = true;
+		result = (struct bpf_sock_tuple *)&iph->saddr;
+	} else if (eth_proto == bpf_htons(ETH_P_IPV6)) {
+		struct ipv6hdr *ip6h = (struct ipv6hdr *)(data + nh_off);
+
+		if (ip6h + 1 > data_end)
+			return NULL;
+		ihl_len = sizeof(*ip6h);
+		proto = ip6h->nexthdr;
+		*ipv4 = true;
+		result = (struct bpf_sock_tuple *)&ip6h->saddr;
+	}
+
+	if (data + nh_off + ihl_len > data_end || proto != IPPROTO_TCP)
+		return NULL;
+
+	return result;
+}
+
+SEC("sk_lookup_success")
+int bpf_sk_lookup_test0(struct __sk_buff *skb)
+{
+	void *data_end = (void *)(long)skb->data_end;
+	void *data = (void *)(long)skb->data;
+	struct ethhdr *eth = (struct ethhdr *)(data);
+	struct bpf_sock_tuple *tuple;
+	struct bpf_sock *sk;
+	size_t tuple_len;
+	bool ipv4;
+
+	if (eth + 1 > data_end)
+		return TC_ACT_SHOT;
+
+	tuple = get_tuple(data, sizeof(*eth), data_end, eth->h_proto, &ipv4);
+	if (!tuple || tuple + sizeof *tuple > data_end)
+		return TC_ACT_SHOT;
+
+	tuple_len = ipv4 ? sizeof(tuple->ipv4) : sizeof(tuple->ipv6);
+	sk = bpf_sk_lookup_tcp(skb, tuple, tuple_len, 0, 0);
+	if (sk)
+		bpf_sk_release(sk);
+	return sk ? TC_ACT_OK : TC_ACT_UNSPEC;
+}
+
+SEC("sk_lookup_success_simple")
+int bpf_sk_lookup_test1(struct __sk_buff *skb)
+{
+	struct bpf_sock_tuple tuple = {};
+	struct bpf_sock *sk;
+
+	sk = bpf_sk_lookup_tcp(skb, &tuple, sizeof(tuple), 0, 0);
+	if (sk)
+		bpf_sk_release(sk);
+	return 0;
+}
+
+SEC("fail_use_after_free")
+int bpf_sk_lookup_uaf(struct __sk_buff *skb)
+{
+	struct bpf_sock_tuple tuple = {};
+	struct bpf_sock *sk;
+	__u32 family = 0;
+
+	sk = bpf_sk_lookup_tcp(skb, &tuple, sizeof(tuple), 0, 0);
+	if (sk) {
+		bpf_sk_release(sk);
+		family = sk->family;
+	}
+	return family;
+}
+
+SEC("fail_modify_sk_pointer")
+int bpf_sk_lookup_modptr(struct __sk_buff *skb)
+{
+	struct bpf_sock_tuple tuple = {};
+	struct bpf_sock *sk;
+	__u32 family;
+
+	sk = bpf_sk_lookup_tcp(skb, &tuple, sizeof(tuple), 0, 0);
+	if (sk) {
+		sk += 1;
+		bpf_sk_release(sk);
+	}
+	return 0;
+}
+
+SEC("fail_modify_sk_or_null_pointer")
+int bpf_sk_lookup_modptr_or_null(struct __sk_buff *skb)
+{
+	struct bpf_sock_tuple tuple = {};
+	struct bpf_sock *sk;
+	__u32 family;
+
+	sk = bpf_sk_lookup_tcp(skb, &tuple, sizeof(tuple), 0, 0);
+	sk += 1;
+	if (sk)
+		bpf_sk_release(sk);
+	return 0;
+}
+
+SEC("fail_no_release")
+int bpf_sk_lookup_test2(struct __sk_buff *skb)
+{
+	struct bpf_sock_tuple tuple = {};
+
+	bpf_sk_lookup_tcp(skb, &tuple, sizeof(tuple), 0, 0);
+	return 0;
+}
+
+SEC("fail_release_twice")
+int bpf_sk_lookup_test3(struct __sk_buff *skb)
+{
+	struct bpf_sock_tuple tuple = {};
+	struct bpf_sock *sk;
+
+	sk = bpf_sk_lookup_tcp(skb, &tuple, sizeof(tuple), 0, 0);
+	bpf_sk_release(sk);
+	bpf_sk_release(sk);
+	return 0;
+}
+
+SEC("fail_release_unchecked")
+int bpf_sk_lookup_test4(struct __sk_buff *skb)
+{
+	struct bpf_sock_tuple tuple = {};
+	struct bpf_sock *sk;
+
+	sk = bpf_sk_lookup_tcp(skb, &tuple, sizeof(tuple), 0, 0);
+	bpf_sk_release(sk);
+	return 0;
+}
+
+void lookup_no_release(struct __sk_buff *skb)
+{
+	struct bpf_sock_tuple tuple = {};
+	bpf_sk_lookup_tcp(skb, &tuple, sizeof(tuple), 0, 0);
+}
+
+SEC("fail_no_release_subcall")
+int bpf_sk_lookup_test5(struct __sk_buff *skb)
+{
+	lookup_no_release(skb);
+	return 0;
+}