From 6668ed271eaefaa63e686bdfbedaeb7b8e492722 Mon Sep 17 00:00:00 2001 From: Kumar Kartikeya Dwivedi Date: Fri, 4 Sep 2026 10:43:19 +0200 Subject: selftests/bpf: Reject graph kptr use after RCU unlock 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 Link: https://lore.kernel.org/r/20260904084325.52250-7-memxor@gmail.com Signed-off-by: Alexei Starovoitov --- fs/fs_pin.c | 97 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 97 insertions(+) create mode 100644 fs/fs_pin.c (limited to 'fs/fs_pin.c') diff --git a/fs/fs_pin.c b/fs/fs_pin.c new file mode 100644 index 000000000..47ef3c71c --- /dev/null +++ b/fs/fs_pin.c @@ -0,0 +1,97 @@ +// SPDX-License-Identifier: GPL-2.0 +#include +#include +#include +#include "internal.h" +#include "mount.h" + +static DEFINE_SPINLOCK(pin_lock); + +void pin_remove(struct fs_pin *pin) +{ + spin_lock(&pin_lock); + hlist_del_init(&pin->m_list); + hlist_del_init(&pin->s_list); + spin_unlock(&pin_lock); + spin_lock_irq(&pin->wait.lock); + pin->done = 1; + wake_up_locked(&pin->wait); + spin_unlock_irq(&pin->wait.lock); +} + +void pin_insert(struct fs_pin *pin, struct vfsmount *m) +{ + spin_lock(&pin_lock); + hlist_add_head(&pin->s_list, &m->mnt_sb->s_pins); + hlist_add_head(&pin->m_list, &real_mount(m)->mnt_pins); + spin_unlock(&pin_lock); +} + +void pin_kill(struct fs_pin *p) +{ + wait_queue_entry_t wait; + + if (!p) { + rcu_read_unlock(); + return; + } + init_wait(&wait); + spin_lock_irq(&p->wait.lock); + if (likely(!p->done)) { + p->done = -1; + spin_unlock_irq(&p->wait.lock); + rcu_read_unlock(); + p->kill(p); + return; + } + if (p->done > 0) { + spin_unlock_irq(&p->wait.lock); + rcu_read_unlock(); + return; + } + __add_wait_queue(&p->wait, &wait); + while (1) { + set_current_state(TASK_UNINTERRUPTIBLE); + spin_unlock_irq(&p->wait.lock); + rcu_read_unlock(); + schedule(); + rcu_read_lock(); + if (likely(list_empty(&wait.entry))) + break; + /* OK, we know p couldn't have been freed yet */ + spin_lock_irq(&p->wait.lock); + if (p->done > 0) { + spin_unlock_irq(&p->wait.lock); + break; + } + } + rcu_read_unlock(); +} + +void mnt_pin_kill(struct mount *m) +{ + while (1) { + struct hlist_node *p; + rcu_read_lock(); + p = READ_ONCE(m->mnt_pins.first); + if (!p) { + rcu_read_unlock(); + break; + } + pin_kill(hlist_entry(p, struct fs_pin, m_list)); + } +} + +void group_pin_kill(struct hlist_head *p) +{ + while (1) { + struct hlist_node *q; + rcu_read_lock(); + q = READ_ONCE(p->first); + if (!q) { + rcu_read_unlock(); + break; + } + pin_kill(hlist_entry(q, struct fs_pin, s_list)); + } +} -- cgit v1.3.1