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Date:   Mon, 25 Oct 2021 14:24:34 -0700
From:   Kees Cook <keescook@chromium.org>
To:     Yafang Shao <laoar.shao@gmail.com>
Cc:     akpm@linux-foundation.org, rostedt@goodmis.org,
        mathieu.desnoyers@efficios.com, arnaldo.melo@gmail.com,
        pmladek@suse.com, peterz@infradead.org, viro@zeniv.linux.org.uk,
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        Andrii Nakryiko <andrii.nakryiko@gmail.com>
Subject: Re: [PATCH v6 08/12] tools/bpf/bpftool/skeleton: make it adopt to
 task comm size change
Message-ID: <202110251421.7056ACF84@keescook>
References: <20211025083315.4752-1-laoar.shao@gmail.com>
 <20211025083315.4752-9-laoar.shao@gmail.com>
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On Mon, Oct 25, 2021 at 08:33:11AM +0000, Yafang Shao wrote:
> bpf_probe_read_kernel_str() will add a nul terminator to the dst, then
> we don't care about if the dst size is big enough.
> 
> Signed-off-by: Yafang Shao <laoar.shao@gmail.com>
> Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
> Cc: Arnaldo Carvalho de Melo <arnaldo.melo@gmail.com>
> Cc: Andrii Nakryiko <andrii.nakryiko@gmail.com>
> Cc: Peter Zijlstra <peterz@infradead.org>
> Cc: Steven Rostedt <rostedt@goodmis.org>
> Cc: Al Viro <viro@zeniv.linux.org.uk>
> Cc: Kees Cook <keescook@chromium.org>
> Cc: Petr Mladek <pmladek@suse.com>

So, if we're ever going to copying these buffers out of the kernel (I
don't know what the object lifetime here in bpf is for "e", etc), we
should be zero-padding (as get_task_comm() does).

Should this, instead, be using a bounce buffer?

get_task_comm(comm, task->group_leader);
bpf_probe_read_kernel_str(&e.comm, sizeof(e.comm), comm);

-Kees

> ---
>  tools/bpf/bpftool/skeleton/pid_iter.bpf.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/tools/bpf/bpftool/skeleton/pid_iter.bpf.c b/tools/bpf/bpftool/skeleton/pid_iter.bpf.c
> index d9b420972934..f70702fcb224 100644
> --- a/tools/bpf/bpftool/skeleton/pid_iter.bpf.c
> +++ b/tools/bpf/bpftool/skeleton/pid_iter.bpf.c
> @@ -71,8 +71,8 @@ int iter(struct bpf_iter__task_file *ctx)
>  
>  	e.pid = task->tgid;
>  	e.id = get_obj_id(file->private_data, obj_type);
> -	bpf_probe_read_kernel(&e.comm, sizeof(e.comm),
> -			      task->group_leader->comm);
> +	bpf_probe_read_kernel_str(&e.comm, sizeof(e.comm),
> +				  task->group_leader->comm);
>  	bpf_seq_write(ctx->meta->seq, &e, sizeof(e));
>  
>  	return 0;
> -- 
> 2.17.1
> 

-- 
Kees Cook