Re: [PATCH 5/7] samples/bpf/test_overhead_kprobe_kern: make it adopt to task comm size change

[David Hildenbrand]

On 08.11.21 09:38, 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>
> Reviewed-by: Kees Cook <keescook@xxxxxxxxxxxx>
> Cc: Mathieu Desnoyers <mathieu.desnoyers@xxxxxxxxxxxx>
> Cc: Arnaldo Carvalho de Melo <arnaldo.melo@xxxxxxxxx>
> Cc: Alexei Starovoitov <alexei.starovoitov@xxxxxxxxx>
> Cc: Andrii Nakryiko <andrii.nakryiko@xxxxxxxxx>
> Cc: Michal Miroslaw <mirq-linux@xxxxxxxxxxxx>
> Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
> Cc: Steven Rostedt <rostedt@xxxxxxxxxxx>
> Cc: Matthew Wilcox <willy@xxxxxxxxxxxxx>
> Cc: David Hildenbrand <david@xxxxxxxxxx>
> Cc: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
> Cc: Kees Cook <keescook@xxxxxxxxxxxx>
> Cc: Petr Mladek <pmladek@xxxxxxxx>
> ---
>  samples/bpf/offwaketime_kern.c          |  4 ++--
>  samples/bpf/test_overhead_kprobe_kern.c | 11 ++++++-----
>  samples/bpf/test_overhead_tp_kern.c     |  5 +++--
>  3 files changed, 11 insertions(+), 9 deletions(-)
> 
> diff --git a/samples/bpf/offwaketime_kern.c b/samples/bpf/offwaketime_kern.c
> index 4866afd054da..eb4d94742e6b 100644
> --- a/samples/bpf/offwaketime_kern.c
> +++ b/samples/bpf/offwaketime_kern.c
> @@ -113,11 +113,11 @@ static inline int update_counts(void *ctx, u32 pid, u64 delta)
>  /* taken from /sys/kernel/debug/tracing/events/sched/sched_switch/format */
>  struct sched_switch_args {
>  	unsigned long long pad;
> -	char prev_comm[16];
> +	char prev_comm[TASK_COMM_LEN];
>  	int prev_pid;
>  	int prev_prio;
>  	long long prev_state;
> -	char next_comm[16];
> +	char next_comm[TASK_COMM_LEN];
>  	int next_pid;
>  	int next_prio;
>  };
> 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));

It's a shame we have to do a manual copy here ...

Changes LGTM

Reviewed-by: David Hildenbrand <david@xxxxxxxxxx>

-- 
Thanks,

David / dhildenb