[PATCH v5 07/15] samples/bpf/kern: use TASK_COMM_LEN instead of hard-coded 16

[Yafang Shao <laoar.shao@gmail.com>]

The linux/sched.h is visible to the bpf kernel modules, so we can use
TASK_COMM_LEN_16 to replace the hard-coded 16 in these bpf kernel
modules to make it more grepable.

In these bpf modules, someone gets task comm via bpf_get_current_comm(),
which always get a nul terminated string. While someone gets task comm via
bpf_probe_read_kernel(), which is unsafe, we should use
bpf_probe_read_kernel_str() instead.

Signed-off-by: Yafang Shao <laoar.shao@gmail.com>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Kees Cook <keescook@chromium.org>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Petr Mladek <pmladek@suse.com>
---
 samples/bpf/offwaketime_kern.c          | 10 +++++-----
 samples/bpf/test_overhead_kprobe_kern.c | 11 ++++++-----
 samples/bpf/test_overhead_tp_kern.c     |  5 +++--
 samples/bpf/tracex2_kern.c              |  3 ++-
 4 files changed, 16 insertions(+), 13 deletions(-)

diff --git a/samples/bpf/offwaketime_kern.c b/samples/bpf/offwaketime_kern.c
index 4866afd054da..c0fd04497eea 100644
--- a/samples/bpf/offwaketime_kern.c
+++ b/samples/bpf/offwaketime_kern.c
@@ -23,8 +23,8 @@
 #define MAX_ENTRIES	10000
 
 struct key_t {
-	char waker[TASK_COMM_LEN];
-	char target[TASK_COMM_LEN];
+	char waker[TASK_COMM_LEN_16];
+	char target[TASK_COMM_LEN_16];
 	u32 wret;
 	u32 tret;
 };
@@ -44,7 +44,7 @@ struct {
 } start SEC(".maps");
 
 struct wokeby_t {
-	char name[TASK_COMM_LEN];
+	char name[TASK_COMM_LEN_16];
 	u32 ret;
 };
 
@@ -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_16];
 	int prev_pid;
 	int prev_prio;
 	long long prev_state;
-	char next_comm[16];
+	char next_comm[TASK_COMM_LEN_16];
 	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..31e8c5ee0cdc 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_16] = {};
+	char newcomm[TASK_COMM_LEN_16] = {};
 	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..a6d5b3301af2 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_16];
+	char newcomm[TASK_COMM_LEN_16];
 	__u16 oom_score_adj;
 };
 SEC("tracepoint/task/task_rename")
diff --git a/samples/bpf/tracex2_kern.c b/samples/bpf/tracex2_kern.c
index 5bc696bac27d..d70ce59055cb 100644
--- a/samples/bpf/tracex2_kern.c
+++ b/samples/bpf/tracex2_kern.c
@@ -7,6 +7,7 @@
 #include <linux/skbuff.h>
 #include <linux/netdevice.h>
 #include <linux/version.h>
+#include <linux/sched.h>
 #include <uapi/linux/bpf.h>
 #include <bpf/bpf_helpers.h>
 #include <bpf/bpf_tracing.h>
@@ -65,7 +66,7 @@ static unsigned int log2l(unsigned long v)
 }
 
 struct hist_key {
-	char comm[16];
+	char comm[TASK_COMM_LEN_16];
 	u64 pid_tgid;
 	u64 uid_gid;
 	u64 index;
-- 
2.17.1