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SubjectRe: [PATCH v3] kernel/kprobes: add re-register safe check for register_kretprobe()
On Fri, 10 Nov 2017 17:28:33 +0800
JianKang Chen <chenjiankang1@huawei.com> wrote:

> From: Chen Jiankang <chenjiankang1@huawei.com>
>
> When there are two same struct kretprobe rp, the INIT_HLIST_HEAD()
> will result in a empty list table rp->free_instances. The memory leak
> will happen. So it needs to add re-register safe check by
> __get_valid_kprobe().

Under rcu read lock :) Please see below comment.

>
> However, current this is not safe for multi-threadings, because
> there is still a chance to re-register kretprobe concurrently.
> So I add a kretprobe_mutex lock to protect the INIT_LIST_HEAD;
>
> Signed-off-by: Chen Jiankang <chenjiankang1@huawei.com>
> ---
> kernel/kprobes.c | 12 +++++++++++-
> 1 file changed, 11 insertions(+), 1 deletion(-)
>
> diff --git a/kernel/kprobes.c b/kernel/kprobes.c
> index a1606a4..5ff8f69 100644
> --- a/kernel/kprobes.c
> +++ b/kernel/kprobes.c
> @@ -67,6 +67,7 @@
>
> /* This protects kprobe_table and optimizing_list */
> static DEFINE_MUTEX(kprobe_mutex);
> +static DEFINE_MUTEX(kretprobe_mutex);
> static DEFINE_PER_CPU(struct kprobe *, kprobe_instance) = NULL;
> static struct {
> raw_spinlock_t lock ____cacheline_aligned_in_smp;
> @@ -1947,6 +1948,12 @@ int register_kretprobe(struct kretprobe *rp)
> rp->maxactive = num_possible_cpus();
> #endif
> }
> +
> + mutex_lock(&kretprobe_mutex);
> + if (__get_valid_kprobe(&rp->kp)) {

__get_valid_kprobe() must be called under rcu_read_lock or preempt disabled,
because it tracks down the rcu list.

Thank you.



> + ret = -EINVAL;
> + goto out;
> + }
> raw_spin_lock_init(&rp->lock);
> INIT_HLIST_HEAD(&rp->free_instances);
> for (i = 0; i < rp->maxactive; i++) {
> @@ -1954,7 +1961,8 @@ int register_kretprobe(struct kretprobe *rp)
> rp->data_size, GFP_KERNEL);
> if (inst == NULL) {
> free_rp_inst(rp);
> - return -ENOMEM;
> + ret = -ENOMEM;
> + goto out;
> }
> INIT_HLIST_NODE(&inst->hlist);
> hlist_add_head(&inst->hlist, &rp->free_instances);
> @@ -1965,6 +1973,8 @@ int register_kretprobe(struct kretprobe *rp)
> ret = register_kprobe(&rp->kp);
> if (ret != 0)
> free_rp_inst(rp);
> +out:
> + mutex_unlock(&kretprobe_mutex);
> return ret;
> }
> EXPORT_SYMBOL_GPL(register_kretprobe);
> --
> 1.7.12.4
>


--
Masami Hiramatsu <mhiramat@kernel.org>

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