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fa9dcacdcd
stack_map_get_build_id_offset() introduced a per-CPU irq_work to defer
mmap_read_unlock() from NMI context, and bpf_find_vma() later reused the
same mmap_unlock_work. Both callers only check whether the work is busy
before taking mmap_lock, so a nested caller can reuse the slot before the
first caller queues it. Two read locks may then be acquired while only one
deferred unlock runs, leaking a read lock and blocking exit_mmap().
Reserve the per-CPU slot before mmap_read_trylock(). Use the same wrapper
in stackmap and bpf_find_vma() so both callers release the reservation on
trylock failure. Keep rejecting the slot while the irq_work remains busy.
Release it after the irq_work callback unlocks the mm.
Fixes: eac9153f2b ("bpf/stackmap: Fix deadlock with rq_lock in bpf_get_stack()")
Reported-by: syzbot+cdd6c0925e12b0af60cc@syzkaller.appspotmail.com
Reported-by: sashiko-bot@kernel.org
Signed-off-by: Sanghyun Park <sanghyun.park.cnu@gmail.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Closes: https://syzkaller.appspot.com/bug?extid=cdd6c0925e12b0af60cc
Closes: https://lore.kernel.org/r/20260630033745.B80201F000E9@smtp.kernel.org
Link: https://lore.kernel.org/bpf/20260805031425.2157475-2-sanghyun.park.cnu@gmail.com
73 lines
1.9 KiB
C
73 lines
1.9 KiB
C
/* SPDX-License-Identifier: GPL-2.0-only */
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/* Copyright (c) 2021 Facebook
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*/
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#ifndef __MMAP_UNLOCK_WORK_H__
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#define __MMAP_UNLOCK_WORK_H__
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#include <linux/atomic.h>
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#include <linux/err.h>
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#include <linux/irq_work.h>
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/* irq_work to run mmap_read_unlock() in irq_work */
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struct mmap_unlock_irq_work {
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struct irq_work irq_work;
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struct mm_struct *mm;
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atomic_t active;
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};
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DECLARE_PER_CPU(struct mmap_unlock_irq_work, mmap_unlock_work);
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/*
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* We cannot do mmap_read_unlock() when the irq is disabled, because of
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* risk to deadlock with rq_lock. To look up vma when the irqs are
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* disabled, we need to run mmap_read_unlock() in irq_work. We use a
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* percpu variable to do the irq_work. The active flag reserves the slot
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* before mmap_read_trylock() and until the irq_work callback consumes mm.
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*/
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static inline struct mmap_unlock_irq_work *bpf_mmap_unlock_guard_get(void)
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{
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struct mmap_unlock_irq_work *work;
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if (!irqs_disabled())
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return NULL;
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/*
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* PREEMPT_RT does not allow to trylock mmap sem in interrupt
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* disabled context. Force the fallback code.
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*/
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if (IS_ENABLED(CONFIG_PREEMPT_RT))
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return ERR_PTR(-EBUSY);
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work = this_cpu_ptr(&mmap_unlock_work);
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if (irq_work_is_busy(&work->irq_work) ||
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atomic_cmpxchg_acquire(&work->active, 0, 1))
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return ERR_PTR(-EBUSY);
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return work;
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}
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static inline void
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bpf_mmap_unlock_guard_put(struct mmap_unlock_irq_work *work)
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{
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if (work)
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atomic_set_release(&work->active, 0);
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}
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static inline void bpf_mmap_unlock_mm(struct mmap_unlock_irq_work *work, struct mm_struct *mm)
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{
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if (!work) {
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mmap_read_unlock(mm);
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} else {
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work->mm = mm;
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/* The lock will be released once we're out of interrupt
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* context. Tell lockdep that we've released it now so
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* it doesn't complain that we forgot to release it.
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*/
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rwsem_release(&mm->mmap_lock.dep_map, _RET_IP_);
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irq_work_queue(&work->irq_work);
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}
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}
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#endif /* __MMAP_UNLOCK_WORK_H__ */
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