linux-kernel - Re: [PATCH v6 06/12] samples/bpf/test_overhead_kprobe_kern: make it adopt to task comm size change

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Message-ID: <202110251420.9D2C7731@keescook>
Date:   Mon, 25 Oct 2021 14:20:45 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Yafang Shao <laoar.shao@...il.com>
Cc:     akpm@...ux-foundation.org, rostedt@...dmis.org,
        mathieu.desnoyers@...icios.com, arnaldo.melo@...il.com,
        pmladek@...e.com, peterz@...radead.org, viro@...iv.linux.org.uk,
        valentin.schneider@....com, qiang.zhang@...driver.com,
        robdclark@...omium.org, christian@...uner.io,
        dietmar.eggemann@....com, mingo@...hat.com, juri.lelli@...hat.com,
        vincent.guittot@...aro.org, davem@...emloft.net, kuba@...nel.org,
        ast@...nel.org, daniel@...earbox.net, andrii@...nel.org,
        kafai@...com, songliubraving@...com, yhs@...com,
        john.fastabend@...il.com, kpsingh@...nel.org,
        dennis.dalessandro@...nelisnetworks.com,
        mike.marciniszyn@...nelisnetworks.com, dledford@...hat.com,
        jgg@...pe.ca, linux-rdma@...r.kernel.org, netdev@...r.kernel.org,
        bpf@...r.kernel.org, linux-perf-users@...r.kernel.org,
        linux-fsdevel@...r.kernel.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, oliver.sang@...el.com, lkp@...el.com,
        Andrii Nakryiko <andrii.nakryiko@...il.com>
Subject: Re: [PATCH v6 06/12] samples/bpf/test_overhead_kprobe_kern: make it
 adopt to task comm size change

On Mon, Oct 25, 2021 at 08:33:09AM +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. This patch also
> replaces the hard-coded 16 with TASK_COMM_LEN to make it adopt to task
> comm size change.
> 
> Signed-off-by: Yafang Shao <laoar.shao@...il.com>
> Cc: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
> Cc: Arnaldo Carvalho de Melo <arnaldo.melo@...il.com>
> Cc: Andrii Nakryiko <andrii.nakryiko@...il.com>
> Cc: Peter Zijlstra <peterz@...radead.org>
> Cc: Steven Rostedt <rostedt@...dmis.org>
> Cc: Al Viro <viro@...iv.linux.org.uk>
> Cc: Kees Cook <keescook@...omium.org>
> Cc: Petr Mladek <pmladek@...e.com>

As these are samples, I guess it's fine to change their sizes.

Reviewed-by: Kees Cook <keescook@...omium.org>

> ---
>  samples/bpf/test_overhead_kprobe_kern.c | 11 ++++++-----
>  samples/bpf/test_overhead_tp_kern.c     |  5 +++--
>  2 files changed, 9 insertions(+), 7 deletions(-)
> 
> diff --git a/samples/bpf/test_overhead_kprobe_kern.c b/samples/bpf/test_overhead_kprobe_kern.c
> index f6d593e47037..8fdd2c9c56b2 100644
> --- a/samples/bpf/test_overhead_kprobe_kern.c
> +++ b/samples/bpf/test_overhead_kprobe_kern.c
> @@ -6,6 +6,7 @@
>   */
>  #include <linux/version.h>
>  #include <linux/ptrace.h>
> +#include <linux/sched.h>
>  #include <uapi/linux/bpf.h>
>  #include <bpf/bpf_helpers.h>
>  #include <bpf/bpf_tracing.h>
> @@ -22,17 +23,17 @@ int prog(struct pt_regs *ctx)
>  {
>  	struct signal_struct *signal;
>  	struct task_struct *tsk;
> -	char oldcomm[16] = {};
> -	char newcomm[16] = {};
> +	char oldcomm[TASK_COMM_LEN] = {};
> +	char newcomm[TASK_COMM_LEN] = {};
>  	u16 oom_score_adj;
>  	u32 pid;
>  
>  	tsk = (void *)PT_REGS_PARM1(ctx);
>  
>  	pid = _(tsk->pid);
> -	bpf_probe_read_kernel(oldcomm, sizeof(oldcomm), &tsk->comm);
> -	bpf_probe_read_kernel(newcomm, sizeof(newcomm),
> -			      (void *)PT_REGS_PARM2(ctx));
> +	bpf_probe_read_kernel_str(oldcomm, sizeof(oldcomm), &tsk->comm);
> +	bpf_probe_read_kernel_str(newcomm, sizeof(newcomm),
> +				  (void *)PT_REGS_PARM2(ctx));
>  	signal = _(tsk->signal);
>  	oom_score_adj = _(signal->oom_score_adj);
>  	return 0;
> diff --git a/samples/bpf/test_overhead_tp_kern.c b/samples/bpf/test_overhead_tp_kern.c
> index eaa32693f8fc..80edadacb692 100644
> --- a/samples/bpf/test_overhead_tp_kern.c
> +++ b/samples/bpf/test_overhead_tp_kern.c
> @@ -4,6 +4,7 @@
>   * modify it under the terms of version 2 of the GNU General Public
>   * License as published by the Free Software Foundation.
>   */
> +#include <linux/sched.h>
>  #include <uapi/linux/bpf.h>
>  #include <bpf/bpf_helpers.h>
>  
> @@ -11,8 +12,8 @@
>  struct task_rename {
>  	__u64 pad;
>  	__u32 pid;
> -	char oldcomm[16];
> -	char newcomm[16];
> +	char oldcomm[TASK_COMM_LEN];
> +	char newcomm[TASK_COMM_LEN];
>  	__u16 oom_score_adj;
>  };
>  SEC("tracepoint/task/task_rename")
> -- 
> 2.17.1
> 

-- 
Kees Cook