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SubjectRe: [PATCH] kprobes: avoid the kprobe being re-registered
On Thu, 26 Oct 2017 20:11:25 +0800
Zhou Chengming <zhouchengming1@huawei.com> wrote:

> Old code use check_kprobe_rereg() to check if the kprobe has been
> registered already, but check_kprobe_rereg() will release the
> kprobe_mutex then, so maybe two paths will pass the check and
> register the same kprobe. This patch put the check inside the mutex.

Still no good, see below comment.

>
> Signed-off-by: Zhou Chengming <zhouchengming1@huawei.com>
> ---
> kernel/kprobes.c | 23 ++++++-----------------
> 1 file changed, 6 insertions(+), 17 deletions(-)
>
> diff --git a/kernel/kprobes.c b/kernel/kprobes.c
> index a1606a4..2a4873a 100644
> --- a/kernel/kprobes.c
> +++ b/kernel/kprobes.c
> @@ -1443,19 +1443,6 @@ static struct kprobe *__get_valid_kprobe(struct kprobe *p)
> return ap;
> }
>
> -/* Return error if the kprobe is being re-registered */
> -static inline int check_kprobe_rereg(struct kprobe *p)
> -{
> - int ret = 0;
> -
> - mutex_lock(&kprobe_mutex);
> - if (__get_valid_kprobe(p))
> - ret = -EINVAL;
> - mutex_unlock(&kprobe_mutex);
> -
> - return ret;
> -}
> -
> int __weak arch_check_ftrace_location(struct kprobe *p)
> {
> unsigned long ftrace_addr;
> @@ -1536,10 +1523,6 @@ int register_kprobe(struct kprobe *p)
> return PTR_ERR(addr);
> p->addr = addr;
>
> - ret = check_kprobe_rereg(p);
> - if (ret)
> - return ret;
> -
> /* User can pass only KPROBE_FLAG_DISABLED to register_kprobe */
> p->flags &= KPROBE_FLAG_DISABLED;
> p->nmissed = 0;

here, we already modifies the kprobe. We need to check and reject before modifying it.

Thank you,

> @@ -1551,6 +1534,12 @@ int register_kprobe(struct kprobe *p)
>
> mutex_lock(&kprobe_mutex);
>
> + /* Return error if the kprobe is being re-registered */
> + if (__get_valid_kprobe(p)) {
> + ret = -EINVAL;
> + goto out;
> + }
> +
> old_p = get_kprobe(p->addr);
> if (old_p) {
> /* Since this may unoptimize old_p, locking text_mutex. */
> --
> 1.8.3.1
>


--
Masami Hiramatsu <mhiramat@kernel.org>

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