selftests/bpf: Reject graph kptr use after RCU unlock

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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>

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Kumar Kartikeya Dwivedi 2026-09-04 10:43:19 +02:00 • committed by Alexei Starovoitov

parent cd6f72d7f3

commit 6668ed271e

2 changed files with 78 additions and 3 deletions

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6

tools/testing/selftests/bpf/progs/rcu_read_lock.c

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75

tools/testing/selftests/bpf/progs/refcounted_kptr_fail.c

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