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, 89 insertions, 0 deletions

diff --git a/fs/nfsd/auth.c b/fs/nfsd/auth.c
new file mode 100644
index 000000000..4dc327e02
--- /dev/null
+++ b/fs/nfsd/auth.c
@@ -0,0 +1,89 @@
+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (C) 1995, 1996 Olaf Kirch <okir@monad.swb.de> */
+
+#include <linux/sched.h>
+#include "nfsd.h"
+#include "auth.h"
+
+int nfsexp_flags(struct svc_cred *cred, struct svc_export *exp)
+{
+	struct exp_flavor_info *f;
+	struct exp_flavor_info *end = exp->ex_flavors + exp->ex_nflavors;
+
+	for (f = exp->ex_flavors; f < end; f++) {
+		if (f->pseudoflavor == cred->cr_flavor)
+			return f->flags;
+	}
+	return exp->ex_flags;
+
+}
+
+int nfsd_setuser(struct svc_cred *cred, struct svc_export *exp)
+{
+	struct group_info *rqgi;
+	struct group_info *gi;
+	struct cred *new;
+	int i;
+	int flags = nfsexp_flags(cred, exp);
+
+	/* discard any old override before preparing the new set */
+	put_cred(revert_creds(get_cred(current_real_cred())));
+	new = prepare_creds();
+	if (!new)
+		return -ENOMEM;
+
+	new->fsuid = cred->cr_uid;
+	new->fsgid = cred->cr_gid;
+
+	rqgi = cred->cr_group_info;
+
+	if (flags & NFSEXP_ALLSQUASH) {
+		new->fsuid = exp->ex_anon_uid;
+		new->fsgid = exp->ex_anon_gid;
+		gi = groups_alloc(0);
+		if (!gi)
+			goto oom;
+	} else if (flags & NFSEXP_ROOTSQUASH) {
+		if (uid_eq(new->fsuid, GLOBAL_ROOT_UID))
+			new->fsuid = exp->ex_anon_uid;
+		if (gid_eq(new->fsgid, GLOBAL_ROOT_GID))
+			new->fsgid = exp->ex_anon_gid;
+
+		gi = groups_alloc(rqgi->ngroups);
+		if (!gi)
+			goto oom;
+
+		for (i = 0; i < rqgi->ngroups; i++) {
+			if (gid_eq(GLOBAL_ROOT_GID, rqgi->gid[i]))
+				gi->gid[i] = exp->ex_anon_gid;
+			else
+				gi->gid[i] = rqgi->gid[i];
+		}
+
+		/* Each thread allocates its own gi, no race */
+		groups_sort(gi);
+	} else {
+		gi = get_group_info(rqgi);
+	}
+
+	if (uid_eq(new->fsuid, INVALID_UID))
+		new->fsuid = exp->ex_anon_uid;
+	if (gid_eq(new->fsgid, INVALID_GID))
+		new->fsgid = exp->ex_anon_gid;
+
+	set_groups(new, gi);
+	put_group_info(gi);
+
+	if (!uid_eq(new->fsuid, GLOBAL_ROOT_UID))
+		new->cap_effective = cap_drop_nfsd_set(new->cap_effective);
+	else
+		new->cap_effective = cap_raise_nfsd_set(new->cap_effective,
+							new->cap_permitted);
+	put_cred(override_creds(new));
+	return 0;
+
+oom:
+	abort_creds(new);
+	return -ENOMEM;
+}
+