linux-kernel - [PATCH v4 5/5] kernel/kthread: show a warning if kthread's comm is truncated

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Date:   Wed, 13 Oct 2021 10:23:46 +0000
From:   Yafang Shao <laoar.shao@...il.com>
To:     keescook@...omium.org, rostedt@...dmis.org, peterz@...radead.org,
        pmladek@...e.com, viro@...iv.linux.org.uk,
        akpm@...ux-foundation.org, valentin.schneider@....com,
        mathieu.desnoyers@...icios.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, bsegall@...gle.com, mgorman@...e.de,
        bristot@...hat.com, davem@...emloft.net, kuba@...nel.org
Cc:     linux-kernel@...r.kernel.org, Yafang Shao <laoar.shao@...il.com>
Subject: [PATCH v4 5/5] kernel/kthread: show a warning if kthread's comm is truncated

Show a warning if task comm is truncated. Below is the result
of my test case:

truncated kthread comm:I-am-a-kthread-with-lon, pid:14 by 6 characters

Suggested-by: Petr Mladek <pmladek@...e.com>
Signed-off-by: Yafang Shao <laoar.shao@...il.com>
Reviewed-by: Kees Cook <keescook@...omium.org>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Steven Rostedt <rostedt@...dmis.org>
Cc: Al Viro <viro@...iv.linux.org.uk>
Cc: Petr Mladek <pmladek@...e.com>
---
 kernel/kthread.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/kernel/kthread.c b/kernel/kthread.c
index 5b37a8567168..46b924c92078 100644
--- a/kernel/kthread.c
+++ b/kernel/kthread.c
@@ -399,12 +399,17 @@ struct task_struct *__kthread_create_on_node(int (*threadfn)(void *data),
 	if (!IS_ERR(task)) {
 		static const struct sched_param param = { .sched_priority = 0 };
 		char name[TASK_COMM_LEN];
+		int len;
 
 		/*
 		 * task is already visible to other tasks, so updating
 		 * COMM must be protected.
 		 */
-		vsnprintf(name, sizeof(name), namefmt, args);
+		len = vsnprintf(name, sizeof(name), namefmt, args);
+		if (len >= TASK_COMM_LEN) {
+			pr_warn("truncated kthread comm:%s, pid:%d by %d characters\n",
+				name, task->pid, len - TASK_COMM_LEN + 1);
+		}
 		set_task_comm(task, name);
 		/*
 		 * root may have changed our (kthreadd's) priority or CPU mask.
-- 
2.17.1