From: Sanghyun Park <sanghyun.park.cnu@gmail.com> mainline inclusion from mainline-v7.3-rc1 commit fa9dcacdcdf487f0ffef64bf67622f1caed509f1 category: bugfix bugzilla: https://atomgit.com/src-openeuler/kernel/issues/19451 Reference: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?i... -------------------------------- 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: eac9153f2b58 ("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... Conflicts: kernel/bpf/stackmap.c [ctx conflicts] Signed-off-by: Pu Lehui <pulehui@huawei.com> --- kernel/bpf/mmap_unlock_work.h | 51 ++++++++++++++++++++--------------- kernel/bpf/stackmap.c | 28 +++++++++++-------- kernel/bpf/task_iter.c | 14 +++++++--- 3 files changed, 56 insertions(+), 37 deletions(-) diff --git a/kernel/bpf/mmap_unlock_work.h b/kernel/bpf/mmap_unlock_work.h index 5d18d7d85bef..1834db20b861 100644 --- a/kernel/bpf/mmap_unlock_work.h +++ b/kernel/bpf/mmap_unlock_work.h @@ -4,12 +4,15 @@ #ifndef __MMAP_UNLOCK_WORK_H__ #define __MMAP_UNLOCK_WORK_H__ +#include <linux/atomic.h> +#include <linux/err.h> #include <linux/irq_work.h> /* irq_work to run mmap_read_unlock() in irq_work */ struct mmap_unlock_irq_work { struct irq_work irq_work; struct mm_struct *mm; + atomic_t active; }; DECLARE_PER_CPU(struct mmap_unlock_irq_work, mmap_unlock_work); @@ -18,32 +21,36 @@ DECLARE_PER_CPU(struct mmap_unlock_irq_work, mmap_unlock_work); * We cannot do mmap_read_unlock() when the irq is disabled, because of * risk to deadlock with rq_lock. To look up vma when the irqs are * disabled, we need to run mmap_read_unlock() in irq_work. We use a - * percpu variable to do the irq_work. If the irq_work is already used - * by another lookup, we fall over. + * percpu variable to do the irq_work. The active flag reserves the slot + * before mmap_read_trylock() and until the irq_work callback consumes mm. */ -static inline bool bpf_mmap_unlock_get_irq_work(struct mmap_unlock_irq_work **work_ptr) +static inline struct mmap_unlock_irq_work *bpf_mmap_unlock_guard_get(void) { - struct mmap_unlock_irq_work *work = NULL; - bool irq_work_busy = false; + struct mmap_unlock_irq_work *work; - if (irqs_disabled()) { - if (!IS_ENABLED(CONFIG_PREEMPT_RT)) { - work = this_cpu_ptr(&mmap_unlock_work); - if (irq_work_is_busy(&work->irq_work)) { - /* cannot queue more up_read, fallback */ - irq_work_busy = true; - } - } else { - /* - * PREEMPT_RT does not allow to trylock mmap sem in - * interrupt disabled context. Force the fallback code. - */ - irq_work_busy = true; - } - } + if (!irqs_disabled()) + return NULL; + + /* + * PREEMPT_RT does not allow to trylock mmap sem in interrupt + * disabled context. Force the fallback code. + */ + if (IS_ENABLED(CONFIG_PREEMPT_RT)) + return ERR_PTR(-EBUSY); + + work = this_cpu_ptr(&mmap_unlock_work); + if (irq_work_is_busy(&work->irq_work) || + atomic_cmpxchg_acquire(&work->active, 0, 1)) + return ERR_PTR(-EBUSY); - *work_ptr = work; - return irq_work_busy; + return work; +} + +static inline void +bpf_mmap_unlock_guard_put(struct mmap_unlock_irq_work *work) +{ + if (work) + atomic_set_release(&work->active, 0); } static inline void bpf_mmap_unlock_mm(struct mmap_unlock_irq_work *work, struct mm_struct *mm) diff --git a/kernel/bpf/stackmap.c b/kernel/bpf/stackmap.c index 577f87d4b36d..a1230e18f8f1 100644 --- a/kernel/bpf/stackmap.c +++ b/kernel/bpf/stackmap.c @@ -181,22 +181,22 @@ static inline void stack_map_build_id_set_valid(struct bpf_stack_build_id *id, static void stack_map_get_build_id_offset(struct bpf_stack_build_id *id_offs, u32 trace_nr, bool user) { - struct mmap_unlock_irq_work *work = NULL; - bool irq_work_busy = bpf_mmap_unlock_get_irq_work(&work); + struct mmap_unlock_irq_work *work; bool has_user_ctx = user && current && current->mm; struct vm_area_struct *vma, *prev_vma = NULL; const unsigned char *prev_build_id = NULL; int i; - /* If the irq_work is in use, fall back to report ips. Same - * fallback is used for kernel stack (!user) on a stackmap with - * build_id. - */ - if (!has_user_ctx || irq_work_busy || !mmap_read_trylock(current->mm)) { - /* cannot access current->mm, fall back to ips */ - for (i = 0; i < trace_nr; i++) - stack_map_build_id_set_ip(&id_offs[i]); - return; + if (!has_user_ctx) + goto fallback; + + work = bpf_mmap_unlock_guard_get(); + if (IS_ERR(work)) + goto fallback; + + if (!mmap_read_trylock(current->mm)) { + bpf_mmap_unlock_guard_put(work); + goto fallback; } for (i = 0; i < trace_nr; i++) { @@ -224,6 +224,12 @@ static void stack_map_get_build_id_offset(struct bpf_stack_build_id *id_offs, prev_build_id = id_offs[i].build_id; } bpf_mmap_unlock_mm(work, current->mm); + return; + +fallback: + /* cannot access current->mm, fall back to ips */ + for (i = 0; i < trace_nr; i++) + stack_map_build_id_set_ip(&id_offs[i]); } static struct perf_callchain_entry * diff --git a/kernel/bpf/task_iter.c b/kernel/bpf/task_iter.c index af8b3e3a002e..5743502ef954 100644 --- a/kernel/bpf/task_iter.c +++ b/kernel/bpf/task_iter.c @@ -784,9 +784,8 @@ static struct bpf_iter_reg task_vma_reg_info = { BPF_CALL_5(bpf_find_vma, struct task_struct *, task, u64, start, bpf_callback_t, callback_fn, void *, callback_ctx, u64, flags) { - struct mmap_unlock_irq_work *work = NULL; + struct mmap_unlock_irq_work *work; struct vm_area_struct *vma; - bool irq_work_busy = false; bool __maybe_unused mmput_needed = false; struct mm_struct *mm; int ret = -ENOENT; @@ -823,9 +822,14 @@ BPF_CALL_5(bpf_find_vma, struct task_struct *, task, u64, start, if (!mm) return -ENOENT; - irq_work_busy = bpf_mmap_unlock_get_irq_work(&work); + work = bpf_mmap_unlock_guard_get(); + if (IS_ERR(work)) { + ret = PTR_ERR(work); + goto out; + } - if (irq_work_busy || !mmap_read_trylock(mm)) { + if (!mmap_read_trylock(mm)) { + bpf_mmap_unlock_guard_put(work); ret = -EBUSY; goto out; } @@ -1225,6 +1229,8 @@ static void do_mmap_read_unlock(struct irq_work *entry) work = container_of(entry, struct mmap_unlock_irq_work, irq_work); mmap_read_unlock_non_owner(work->mm); + work->mm = NULL; + bpf_mmap_unlock_guard_put(work); } static int __init task_iter_init(void) -- 2.34.1