linux-kernel - [PATCH 2/5] kernel/fork: allocate task->comm dynamicly

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Message-Id: <20210929115036.4851-3-laoar.shao@gmail.com>
Date:   Wed, 29 Sep 2021 11:50:33 +0000
From:   Yafang Shao <laoar.shao@...il.com>
To:     akpm@...ux-foundation.org, pmladek@...e.com, peterz@...radead.org,
        valentin.schneider@....com, keescook@...omium.org,
        mathieu.desnoyers@...icios.com, qiang.zhang@...driver.com,
        robdclark@...omium.org, viro@...iv.linux.org.uk,
        christian@...uner.io, dietmar.eggemann@....com
Cc:     linux-kernel@...r.kernel.org, Yafang Shao <laoar.shao@...il.com>
Subject: [PATCH 2/5] kernel/fork: allocate task->comm dynamicly

task->comm is defined as an array embedded in struct task_struct before.
This patch changes it to a char pointer. It will be allocated in the fork
and freed when the task is freed.

Signed-off-by: Yafang Shao <laoar.shao@...il.com>
---
 include/linux/sched.h |  2 +-
 kernel/fork.c         | 19 +++++++++++++++++++
 2 files changed, 20 insertions(+), 1 deletion(-)

diff --git a/include/linux/sched.h b/include/linux/sched.h
index e12b524426b0..b387b5943db4 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1051,7 +1051,7 @@ struct task_struct {
 	 * - access it with [gs]et_task_comm()
 	 * - lock it with task_lock()
 	 */
-	char				comm[TASK_COMM_LEN];
+	char				*comm;
 
 	struct nameidata		*nameidata;
 
diff --git a/kernel/fork.c b/kernel/fork.c
index 38681ad44c76..227aec240501 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -721,6 +721,20 @@ static void mmdrop_async(struct mm_struct *mm)
 	}
 }
 
+static int task_comm_alloc(struct task_struct *p)
+{
+	p->comm = kzalloc(TASK_COMM_LEN, GFP_KERNEL);
+	if (!p->comm)
+		return -ENOMEM;
+
+	return 0;
+}
+
+static void task_comm_free(struct task_struct *p)
+{
+	kfree(p->comm);
+}
+
 static inline void free_signal_struct(struct signal_struct *sig)
 {
 	taskstats_tgid_free(sig);
@@ -753,6 +767,7 @@ void __put_task_struct(struct task_struct *tsk)
 	bpf_task_storage_free(tsk);
 	exit_creds(tsk);
 	delayacct_tsk_free(tsk);
+	task_comm_free(tsk);
 	put_signal_struct(tsk->signal);
 	sched_core_free(tsk);
 
@@ -2076,6 +2091,10 @@ static __latent_entropy struct task_struct *copy_process(
 	if (data_race(nr_threads >= max_threads))
 		goto bad_fork_cleanup_count;
 
+	retval = task_comm_alloc(p);
+	if (retval)
+		goto bad_fork_cleanup_count;
+
 	delayacct_tsk_init(p);	/* Must remain after dup_task_struct() */
 	p->flags &= ~(PF_SUPERPRIV | PF_WQ_WORKER | PF_IDLE | PF_NO_SETAFFINITY);
 	p->flags |= PF_FORKNOEXEC;
-- 
2.17.1