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

[Kees Cook]

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@xxxxxxxxx>
> Cc: Mathieu Desnoyers <mathieu.desnoyers@xxxxxxxxxxxx>
> Cc: Arnaldo Carvalho de Melo <arnaldo.melo@xxxxxxxxx>
> Cc: Andrii Nakryiko <andrii.nakryiko@xxxxxxxxx>
> Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
> Cc: Steven Rostedt <rostedt@xxxxxxxxxxx>
> Cc: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
> Cc: Kees Cook <keescook@xxxxxxxxxxxx>
> Cc: Petr Mladek <pmladek@xxxxxxxx>

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

Reviewed-by: Kees Cook <keescook@xxxxxxxxxxxx>

> ---
>  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