Re: [PATCH v2] kprobes: Skip clearing aggrprobe's post_handler in kprobe-on-ftrace case

[Google]

On Sat, 12 Nov 2022 15:00:00 +0800
Li Huafei <lihuafei1@xxxxxxxxxx> wrote:

> In __unregister_kprobe_top(), if the currently unregistered probe has
> post_handler but other child probes of the aggrprobe do not have
> post_handler, the post_handler of the aggrprobe is cleared. If this is
> a ftrace-based probe, there is a problem. In later calls to
> disarm_kprobe(), we will use kprobe_ftrace_ops because post_handler is
> NULL. But we're armed with kprobe_ipmodify_ops. This triggers a WARN in
> __disarm_kprobe_ftrace() and may even cause use-after-free:
> 
>   Failed to disarm kprobe-ftrace at kernel_clone+0x0/0x3c0 (error -2)
>   WARNING: CPU: 5 PID: 137 at kernel/kprobes.c:1135 __disarm_kprobe_ftrace.isra.21+0xcf/0xe0
>   Modules linked in: testKprobe_007(-)
>   CPU: 5 PID: 137 Comm: rmmod Not tainted 6.1.0-rc4-dirty #18
>   [...]
>   Call Trace:
>    <TASK>
>    __disable_kprobe+0xcd/0xe0
>    __unregister_kprobe_top+0x12/0x150
>    ? mutex_lock+0xe/0x30
>    unregister_kprobes.part.23+0x31/0xa0
>    unregister_kprobe+0x32/0x40
>    __x64_sys_delete_module+0x15e/0x260
>    ? do_user_addr_fault+0x2cd/0x6b0
>    do_syscall_64+0x3a/0x90
>    entry_SYSCALL_64_after_hwframe+0x63/0xcd
>    [...]
> 
> For the kprobe-on-ftrace case, we keep the post_handler setting to
> identify this aggrprobe armed with kprobe_ipmodify_ops. This way we
> can disarm it correctly.

This looks good to me. Thanks!

Acked-by: Masami Hiramatsu (Google) <mhiramat@xxxxxxxxxx>

> 
> Fixes: 0bc11ed5ab60 ("kprobes: Allow kprobes coexist with livepatch")
> Reported-by: Zhao Gongyi <zhaogongyi@xxxxxxxxxx>
> Suggested-by: Masami Hiramatsu (Google) <mhiramat@xxxxxxxxxx>
> Signed-off-by: Li Huafei <lihuafei1@xxxxxxxxxx>
> ---
>  kernel/kprobes.c | 8 +++++++-
>  1 file changed, 7 insertions(+), 1 deletion(-)
> 
> diff --git a/kernel/kprobes.c b/kernel/kprobes.c
> index cd9f5a66a690..3050631e528d 100644
> --- a/kernel/kprobes.c
> +++ b/kernel/kprobes.c
> @@ -1766,7 +1766,13 @@ static int __unregister_kprobe_top(struct kprobe *p)
>  				if ((list_p != p) && (list_p->post_handler))
>  					goto noclean;
>  			}
> -			ap->post_handler = NULL;
> +			/*
> +			 * For the kprobe-on-ftrace case, we keep the
> +			 * post_handler setting to identify this aggrprobe
> +			 * armed with kprobe_ipmodify_ops.
> +			 */
> +			if (!kprobe_ftrace(ap))
> +				ap->post_handler = NULL;
>  		}
>  noclean:
>  		/*
> -- 
> 2.17.1
> 


-- 
Masami Hiramatsu (Google) <mhiramat@xxxxxxxxxx>