selftests/bpf: Reject graph kptr use after RCU unlockgrafted

Add a sleepable verifier test that loads a graph-node local kptr in an
explicit RCU read-side critical section, then passes its node to
bpf_rbtree_remove() after the section ends.

Before the verifier fix, the stale NON_OWN_REF flag makes the node look like
a live borrowed reference and the program is accepted. After the fix, the
pointer is demoted without NON_OWN_REF and the graph kfunc argument is
rejected.

Also exercise a graph kptr loaded while a spin lock provides implicit RCU
protection. The pointer must be invalidated when the lock is released, which
guards the required ordering between non-owning-reference invalidation and
RCU demotion.

Update the existing fault-protected load test state description. The
post-unlock pointer no longer carries NON_OWN_REF, but remains readable
because the load is rewritten to use BPF_PROBE_MEM.

Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
Link: https://lore.kernel.org/r/20260904084325.52250-7-memxor@gmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

1 files changed, 253 insertions, 0 deletions

diff --git a/include/net/request_sock.h b/include/net/request_sock.h
new file mode 100644
index 000000000..5a9c826a7
--- /dev/null
+++ b/include/net/request_sock.h
@@ -0,0 +1,253 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+/*
+ * NET		Generic infrastructure for Network protocols.
+ *
+ *		Definitions for request_sock
+ *
+ * Authors:	Arnaldo Carvalho de Melo <acme@conectiva.com.br>
+ *
+ * 		From code originally in include/net/tcp.h
+ */
+#ifndef _REQUEST_SOCK_H
+#define _REQUEST_SOCK_H
+
+#include <linux/slab.h>
+#include <linux/spinlock.h>
+#include <linux/types.h>
+#include <linux/bug.h>
+#include <linux/refcount.h>
+
+#include <net/sock.h>
+#include <net/rstreason.h>
+
+struct request_sock;
+struct sk_buff;
+struct dst_entry;
+struct proto;
+
+struct request_sock_ops {
+	int		family;
+	unsigned int	obj_size;
+	struct kmem_cache	*slab;
+	char		*slab_name;
+	void		(*send_ack)(const struct sock *sk, struct sk_buff *skb,
+				    struct request_sock *req);
+	void		(*send_reset)(const struct sock *sk,
+				      struct sk_buff *skb,
+				      enum sk_rst_reason reason);
+	void		(*destructor)(struct request_sock *req);
+};
+
+struct saved_syn {
+	u32 mac_hdrlen;
+	u32 network_hdrlen;
+	u32 tcp_hdrlen;
+	u8 data[];
+};
+
+/* struct request_sock - mini sock to represent a connection request
+ */
+struct request_sock {
+	struct sock_common		__req_common;
+#define rsk_refcnt			__req_common.skc_refcnt
+#define rsk_hash			__req_common.skc_hash
+#define rsk_listener			__req_common.skc_listener
+#define rsk_window_clamp		__req_common.skc_window_clamp
+#define rsk_rcv_wnd			__req_common.skc_rcv_wnd
+
+	struct request_sock		*dl_next;
+	u16				mss;
+	u8				num_retrans; /* number of retransmits */
+	u8				syncookie:1; /* True if
+						      * 1) tcpopts needs to be encoded in
+						      *    TS of SYN+ACK
+						      * 2) ACK is validated by BPF kfunc.
+						      */
+	u8				num_timeout:7; /* number of timeouts */
+	u32				ts_recent;
+	struct timer_list		rsk_timer;
+	const struct request_sock_ops	*rsk_ops;
+	struct sock			*sk;
+	struct saved_syn		*saved_syn;
+	u32				secid;
+	u32				peer_secid;
+	u32				timeout;
+};
+
+static inline struct request_sock *inet_reqsk(const struct sock *sk)
+{
+	return (struct request_sock *)sk;
+}
+
+static inline struct sock *req_to_sk(struct request_sock *req)
+{
+	return (struct sock *)req;
+}
+
+/**
+ * skb_steal_sock - steal a socket from an sk_buff
+ * @skb: sk_buff to steal the socket from
+ * @refcounted: is set to true if the socket is reference-counted
+ * @prefetched: is set to true if the socket was assigned from bpf
+ */
+static inline struct sock *skb_steal_sock(struct sk_buff *skb,
+					  bool *refcounted, bool *prefetched)
+{
+	struct sock *sk = skb->sk;
+
+	if (!sk) {
+		*prefetched = false;
+		*refcounted = false;
+		return NULL;
+	}
+
+	*prefetched = skb_sk_is_prefetched(skb);
+	if (*prefetched) {
+#if IS_ENABLED(CONFIG_SYN_COOKIES)
+		if (sk->sk_state == TCP_NEW_SYN_RECV && inet_reqsk(sk)->syncookie) {
+			struct request_sock *req = inet_reqsk(sk);
+
+			*refcounted = false;
+			sk = req->rsk_listener;
+			req->rsk_listener = NULL;
+			return sk;
+		}
+#endif
+		*refcounted = sk_is_refcounted(sk);
+	} else {
+		*refcounted = true;
+	}
+
+	skb->destructor = NULL;
+	skb->sk = NULL;
+	return sk;
+}
+
+void __reqsk_free(struct request_sock *req);
+
+static inline void reqsk_free(struct request_sock *req)
+{
+	DEBUG_NET_WARN_ON_ONCE(refcount_read(&req->rsk_refcnt) != 0);
+	__reqsk_free(req);
+}
+
+static inline void reqsk_put(struct request_sock *req)
+{
+	if (refcount_dec_and_test(&req->rsk_refcnt))
+		__reqsk_free(req);
+}
+
+/*
+ * For a TCP Fast Open listener -
+ *	lock - protects the access to all the reqsk, which is co-owned by
+ *		the listener and the child socket.
+ *	qlen - pending TFO requests (still in TCP_SYN_RECV).
+ *	max_qlen - max TFO reqs allowed before TFO is disabled.
+ *
+ *	XXX (TFO) - ideally these fields can be made as part of "listen_sock"
+ *	structure above. But there is some implementation difficulty due to
+ *	listen_sock being part of request_sock_queue hence will be freed when
+ *	a listener is stopped. But TFO related fields may continue to be
+ *	accessed even after a listener is closed, until its sk_refcnt drops
+ *	to 0 implying no more outstanding TFO reqs. One solution is to keep
+ *	listen_opt around until	sk_refcnt drops to 0. But there is some other
+ *	complexity that needs to be resolved. E.g., a listener can be disabled
+ *	temporarily through shutdown()->tcp_disconnect(), and re-enabled later.
+ */
+struct fastopen_queue {
+	struct request_sock	*rskq_rst_head; /* Keep track of past TFO */
+	struct request_sock	*rskq_rst_tail; /* requests that caused RST.
+						 * This is part of the defense
+						 * against spoofing attack.
+						 */
+	spinlock_t	lock;
+	int		qlen;		/* # of pending (TCP_SYN_RECV) reqs */
+	int		max_qlen;	/* != 0 iff TFO is currently enabled */
+
+	struct tcp_fastopen_context __rcu *ctx; /* cipher context for cookie */
+};
+
+/** struct request_sock_queue - queue of request_socks
+ *
+ * @rskq_accept_head - FIFO head of established children
+ * @rskq_accept_tail - FIFO tail of established children
+ * @rskq_defer_accept - User waits for some data after accept()
+ *
+ */
+struct request_sock_queue {
+	spinlock_t		rskq_lock;
+	u8			rskq_defer_accept;
+	u8			synflood_warned;
+
+	atomic_t		qlen;
+	atomic_t		young;
+
+	struct request_sock	*rskq_accept_head;
+	struct request_sock	*rskq_accept_tail;
+	struct fastopen_queue	fastopenq;  /* Check max_qlen != 0 to determine
+					     * if TFO is enabled.
+					     */
+};
+
+void reqsk_fastopen_remove(struct sock *sk, struct request_sock *req,
+			   bool reset);
+
+static inline bool reqsk_queue_empty(const struct request_sock_queue *queue)
+{
+	return READ_ONCE(queue->rskq_accept_head) == NULL;
+}
+
+static inline struct request_sock *reqsk_queue_remove(struct request_sock_queue *queue,
+						      struct sock *parent)
+{
+	struct request_sock *req;
+
+	spin_lock_bh(&queue->rskq_lock);
+	req = queue->rskq_accept_head;
+	if (req) {
+		sk_acceptq_removed(parent);
+		WRITE_ONCE(queue->rskq_accept_head, req->dl_next);
+		if (queue->rskq_accept_head == NULL)
+			queue->rskq_accept_tail = NULL;
+	}
+	spin_unlock_bh(&queue->rskq_lock);
+	return req;
+}
+
+static inline void reqsk_queue_removed(struct request_sock_queue *queue,
+				       const struct request_sock *req)
+{
+	if (req->num_timeout == 0)
+		atomic_dec(&queue->young);
+	atomic_dec(&queue->qlen);
+}
+
+static inline void reqsk_queue_added(struct request_sock_queue *queue)
+{
+	atomic_inc(&queue->young);
+	atomic_inc(&queue->qlen);
+}
+
+static inline int reqsk_queue_len(const struct request_sock_queue *queue)
+{
+	return atomic_read(&queue->qlen);
+}
+
+static inline int reqsk_queue_len_young(const struct request_sock_queue *queue)
+{
+	return atomic_read(&queue->young);
+}
+
+/* RFC 7323 2.3 Using the Window Scale Option
+ *  The window field (SEG.WND) of every outgoing segment, with the
+ *  exception of <SYN> segments, MUST be right-shifted by
+ *  Rcv.Wind.Shift bits.
+ *
+ * This means the SEG.WND carried in SYNACK can not exceed 65535.
+ * We use this property to harden TCP stack while in NEW_SYN_RECV state.
+ */
+static inline u32 tcp_synack_window(const struct request_sock *req)
+{
+	return min(req->rsk_rcv_wnd, 65535U);
+}
+#endif /* _REQUEST_SOCK_H */