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, 310 insertions, 0 deletions

diff --git a/fs/afs/vl_probe.c b/fs/afs/vl_probe.c
new file mode 100644
index 000000000..3d2e0c925
--- /dev/null
+++ b/fs/afs/vl_probe.c
@@ -0,0 +1,310 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/* AFS vlserver probing
+ *
+ * Copyright (C) 2018 Red Hat, Inc. All Rights Reserved.
+ * Written by David Howells (dhowells@redhat.com)
+ */
+
+#include <linux/sched.h>
+#include <linux/slab.h>
+#include "afs_fs.h"
+#include "internal.h"
+#include "protocol_yfs.h"
+
+
+/*
+ * Handle the completion of a set of probes.
+ */
+static void afs_finished_vl_probe(struct afs_vlserver *server)
+{
+	if (!(server->probe.flags & AFS_VLSERVER_PROBE_RESPONDED)) {
+		server->rtt = UINT_MAX;
+		clear_bit(AFS_VLSERVER_FL_RESPONDING, &server->flags);
+	}
+
+	clear_bit_unlock(AFS_VLSERVER_FL_PROBING, &server->flags);
+	wake_up_bit(&server->flags, AFS_VLSERVER_FL_PROBING);
+}
+
+/*
+ * Handle the completion of a probe RPC call.
+ */
+static void afs_done_one_vl_probe(struct afs_vlserver *server, bool wake_up)
+{
+	if (atomic_dec_and_test(&server->probe_outstanding)) {
+		afs_finished_vl_probe(server);
+		wake_up = true;
+	}
+
+	if (wake_up)
+		wake_up_all(&server->probe_wq);
+}
+
+/*
+ * Process the result of probing a vlserver.  This is called after successful
+ * or failed delivery of an VL.GetCapabilities operation.
+ */
+void afs_vlserver_probe_result(struct afs_call *call)
+{
+	struct afs_addr_list *alist = call->vl_probe;
+	struct afs_vlserver *server = call->vlserver;
+	struct afs_address *addr = &alist->addrs[call->probe_index];
+	unsigned int server_index = call->server_index;
+	unsigned int rtt_us = 0;
+	unsigned int index = call->probe_index;
+	bool have_result = false;
+	int ret = call->error;
+
+	_enter("%s,%u,%u,%d,%d", server->name, server_index, index, ret, call->abort_code);
+
+	spin_lock(&server->probe_lock);
+
+	switch (ret) {
+	case 0:
+		server->probe.error = 0;
+		goto responded;
+	case -ECONNABORTED:
+		if (!(server->probe.flags & AFS_VLSERVER_PROBE_RESPONDED)) {
+			server->probe.abort_code = call->abort_code;
+			server->probe.error = ret;
+		}
+		goto responded;
+	case -ENOMEM:
+	case -ENONET:
+	case -EKEYEXPIRED:
+	case -EKEYREVOKED:
+	case -EKEYREJECTED:
+		server->probe.flags |= AFS_VLSERVER_PROBE_LOCAL_FAILURE;
+		if (server->probe.error == 0)
+			server->probe.error = ret;
+		trace_afs_io_error(call->debug_id, ret, afs_io_error_vl_probe_fail);
+		goto out;
+	case -ECONNRESET: /* Responded, but call expired. */
+	case -ERFKILL:
+	case -EADDRNOTAVAIL:
+	case -ENETUNREACH:
+	case -EHOSTUNREACH:
+	case -EHOSTDOWN:
+	case -ECONNREFUSED:
+	case -ETIMEDOUT:
+	case -ETIME:
+	default:
+		clear_bit(index, &alist->responded);
+		set_bit(index, &alist->probe_failed);
+		if (!(server->probe.flags & AFS_VLSERVER_PROBE_RESPONDED) &&
+		    (server->probe.error == 0 ||
+		     server->probe.error == -ETIMEDOUT ||
+		     server->probe.error == -ETIME))
+			server->probe.error = ret;
+		trace_afs_io_error(call->debug_id, ret, afs_io_error_vl_probe_fail);
+		goto out;
+	}
+
+responded:
+	set_bit(index, &alist->responded);
+	clear_bit(index, &alist->probe_failed);
+
+	if (call->service_id == YFS_VL_SERVICE) {
+		server->probe.flags |= AFS_VLSERVER_PROBE_IS_YFS;
+		set_bit(AFS_VLSERVER_FL_IS_YFS, &server->flags);
+		server->service_id = call->service_id;
+	} else {
+		server->probe.flags |= AFS_VLSERVER_PROBE_NOT_YFS;
+		if (!(server->probe.flags & AFS_VLSERVER_PROBE_IS_YFS)) {
+			clear_bit(AFS_VLSERVER_FL_IS_YFS, &server->flags);
+			server->service_id = call->service_id;
+		}
+	}
+
+	rtt_us = rxrpc_kernel_get_srtt(addr->peer);
+	if (rtt_us < server->probe.rtt) {
+		server->probe.rtt = rtt_us;
+		server->rtt = rtt_us;
+		alist->preferred = index;
+	}
+
+	smp_wmb(); /* Set rtt before responded. */
+	server->probe.flags |= AFS_VLSERVER_PROBE_RESPONDED;
+	set_bit(AFS_VLSERVER_FL_PROBED, &server->flags);
+	set_bit(AFS_VLSERVER_FL_RESPONDING, &server->flags);
+	have_result = true;
+out:
+	spin_unlock(&server->probe_lock);
+
+	trace_afs_vl_probe(server, false, alist, index, call->error, call->abort_code, rtt_us);
+	_debug("probe [%u][%u] %pISpc rtt=%d ret=%d",
+	       server_index, index, rxrpc_kernel_remote_addr(addr->peer),
+	       rtt_us, ret);
+
+	afs_done_one_vl_probe(server, have_result);
+}
+
+/*
+ * Probe all of a vlserver's addresses to find out the best route and to
+ * query its capabilities.
+ */
+static bool afs_do_probe_vlserver(struct afs_net *net,
+				  struct afs_vlserver *server,
+				  struct key *key,
+				  unsigned int server_index,
+				  struct afs_error *_e)
+{
+	struct afs_addr_list *alist;
+	struct afs_call *call;
+	unsigned long unprobed;
+	unsigned int index, i;
+	bool in_progress = false;
+	int best_prio;
+
+	_enter("%s", server->name);
+
+	read_lock(&server->lock);
+	alist = rcu_dereference_protected(server->addresses,
+					  lockdep_is_held(&server->lock));
+	afs_get_addrlist(alist, afs_alist_trace_get_vlprobe);
+	read_unlock(&server->lock);
+
+	atomic_set(&server->probe_outstanding, alist->nr_addrs);
+	memset(&server->probe, 0, sizeof(server->probe));
+	server->probe.rtt = UINT_MAX;
+
+	unprobed = (1UL << alist->nr_addrs) - 1;
+	while (unprobed) {
+		best_prio = -1;
+		index = 0;
+		for (i = 0; i < alist->nr_addrs; i++) {
+			if (test_bit(i, &unprobed) &&
+			    alist->addrs[i].prio > best_prio) {
+				index = i;
+				best_prio = alist->addrs[i].prio;
+			}
+		}
+		__clear_bit(index, &unprobed);
+
+		trace_afs_vl_probe(server, true, alist, index, 0, 0, 0);
+		call = afs_vl_get_capabilities(net, alist, index, key, server,
+					       server_index);
+		if (!IS_ERR(call)) {
+			afs_prioritise_error(_e, call->error, call->abort_code);
+			afs_put_call(call);
+			in_progress = true;
+		} else {
+			afs_prioritise_error(_e, PTR_ERR(call), 0);
+			afs_done_one_vl_probe(server, false);
+		}
+	}
+
+	afs_put_addrlist(alist, afs_alist_trace_put_vlprobe);
+	return in_progress;
+}
+
+/*
+ * Send off probes to all unprobed servers.
+ */
+int afs_send_vl_probes(struct afs_net *net, struct key *key,
+		       struct afs_vlserver_list *vllist)
+{
+	struct afs_vlserver *server;
+	struct afs_error e = {};
+	bool in_progress = false;
+	int i;
+
+	for (i = 0; i < vllist->nr_servers; i++) {
+		server = vllist->servers[i].server;
+		if (test_bit(AFS_VLSERVER_FL_PROBED, &server->flags))
+			continue;
+
+		if (!test_and_set_bit_lock(AFS_VLSERVER_FL_PROBING, &server->flags) &&
+		    afs_do_probe_vlserver(net, server, key, i, &e))
+			in_progress = true;
+	}
+
+	return in_progress ? 0 : e.error;
+}
+
+/*
+ * Wait for the first as-yet untried server to respond.
+ */
+int afs_wait_for_vl_probes(struct afs_vlserver_list *vllist,
+			   unsigned long untried)
+{
+	struct wait_queue_entry *waits;
+	struct afs_vlserver *server;
+	unsigned int rtt = UINT_MAX, rtt_s;
+	bool have_responders = false;
+	int pref = -1, i;
+
+	_enter("%u,%lx", vllist->nr_servers, untried);
+
+	/* Only wait for servers that have a probe outstanding. */
+	for (i = 0; i < vllist->nr_servers; i++) {
+		if (test_bit(i, &untried)) {
+			server = vllist->servers[i].server;
+			if (!test_bit(AFS_VLSERVER_FL_PROBING, &server->flags))
+				__clear_bit(i, &untried);
+			if (server->probe.flags & AFS_VLSERVER_PROBE_RESPONDED)
+				have_responders = true;
+		}
+	}
+	if (have_responders || !untried)
+		return 0;
+
+	waits = kmalloc(array_size(vllist->nr_servers, sizeof(*waits)), GFP_KERNEL);
+	if (!waits)
+		return -ENOMEM;
+
+	for (i = 0; i < vllist->nr_servers; i++) {
+		if (test_bit(i, &untried)) {
+			server = vllist->servers[i].server;
+			init_waitqueue_entry(&waits[i], current);
+			add_wait_queue(&server->probe_wq, &waits[i]);
+		}
+	}
+
+	for (;;) {
+		bool still_probing = false;
+
+		set_current_state(TASK_INTERRUPTIBLE);
+		for (i = 0; i < vllist->nr_servers; i++) {
+			if (test_bit(i, &untried)) {
+				server = vllist->servers[i].server;
+				if (server->probe.flags & AFS_VLSERVER_PROBE_RESPONDED)
+					goto stop;
+				if (test_bit(AFS_VLSERVER_FL_PROBING, &server->flags))
+					still_probing = true;
+			}
+		}
+
+		if (!still_probing || signal_pending(current))
+			goto stop;
+		schedule();
+	}
+
+stop:
+	set_current_state(TASK_RUNNING);
+
+	for (i = 0; i < vllist->nr_servers; i++) {
+		if (test_bit(i, &untried)) {
+			server = vllist->servers[i].server;
+			rtt_s = READ_ONCE(server->rtt);
+			if (test_bit(AFS_VLSERVER_FL_RESPONDING, &server->flags) &&
+			    rtt_s < rtt) {
+				pref = i;
+				rtt = rtt_s;
+			}
+
+			remove_wait_queue(&server->probe_wq, &waits[i]);
+		}
+	}
+
+	kfree(waits);
+
+	if (pref == -1 && signal_pending(current))
+		return -ERESTARTSYS;
+
+	if (pref >= 0)
+		vllist->preferred = pref;
+
+	_leave(" = 0 [%u]", pref);
+	return 0;
+}