In order to increase the size of current->comm[] and to avoid breaking any
existing code, replace memcpy() with copy_task_comm(). This new function
makes sure that the copy is NUL terminated. This is crucial given that the
source buffer might be larger than the destination buffer and could
truncate the NUL character out of it.

Signed-off-by: André Almeida <andrealmeid@igalia.com>
---
Changes from v3:
 - Simplify copy_task_comm() to a memcpy + NUL char at the end of buffer

Changes from v2:
 - Bring back custom function.

Changes from v1:
 - New patch, dropped strtostr() from last version
---
 include/linux/coredump.h        |  2 +-
 include/linux/sched.h           | 11 +++++++++++
 include/linux/tracepoint.h      |  4 ++--
 include/trace/events/block.h    | 10 +++++-----
 include/trace/events/coredump.h |  2 +-
 include/trace/events/f2fs.h     |  4 ++--
 include/trace/events/oom.h      |  2 +-
 include/trace/events/osnoise.h  |  2 +-
 include/trace/events/sched.h    | 10 +++++-----
 include/trace/events/signal.h   |  2 +-
 include/trace/events/task.h     |  7 ++++---
 kernel/printk/nbcon.c           |  2 +-
 kernel/printk/printk.c          |  2 +-
 13 files changed, 36 insertions(+), 24 deletions(-)

diff --git a/include/linux/coredump.h b/include/linux/coredump.h
index 7b38ee2e7913..dee82e3c350a 100644
--- a/include/linux/coredump.h
+++ b/include/linux/coredump.h
@@ -58,7 +58,7 @@ extern void vfs_coredump(const kernel_siginfo_t *siginfo);
 	do {	\
 		char comm[TASK_COMM_LEN];	\
 		/* This will always be NUL terminated. */ \
-		memcpy(comm, current->comm, sizeof(comm)); \
+		copy_task_comm(comm, current, sizeof(comm)); \
 		printk_ratelimited(Level "coredump: %d(%*pE): " Format "\n",	\
 			task_tgid_vnr(current), (int)strlen(comm), comm, ##__VA_ARGS__);	\
 	} while (0)	\
diff --git a/include/linux/sched.h b/include/linux/sched.h
index 2714c81bc708..9b6a413f6618 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -2021,6 +2021,17 @@ extern void __set_task_comm(struct task_struct *tsk, const char *from, bool exec
 	__set_task_comm(tsk, from, false);		\
 })
 
+/*
+ * Copy task name to a buffer. Final result is always a NUL-terminated string.
+ */
+static __always_inline void copy_task_comm(char *dst, struct task_struct *tsk, size_t len)
+{
+	const char *_src = tsk->comm;
+
+	memcpy(dst, _src, len);
+	dst[len - 1] = '\0';
+}
+
 static __always_inline void scheduler_ipi(void)
 {
 	/*
diff --git a/include/linux/tracepoint.h b/include/linux/tracepoint.h
index e0d838c9ce93..9b0094fa44c6 100644
--- a/include/linux/tracepoint.h
+++ b/include/linux/tracepoint.h
@@ -637,10 +637,10 @@ static inline struct tracepoint *tracepoint_ptr_deref(tracepoint_ptr_t *p)
  *	*
  *
  *	TP_fast_assign(
- *		memcpy(__entry->next_comm, next->comm, TASK_COMM_LEN);
+ *		copy_task_comm(__entry->next_comm, next, TASK_COMM_LEN);
  *		__entry->prev_pid	= prev->pid;
  *		__entry->prev_prio	= prev->prio;
- *		memcpy(__entry->prev_comm, prev->comm, TASK_COMM_LEN);
+ *		copy_task_comm(__entry->prev_comm, prev, TASK_COMM_LEN);
  *		__entry->next_pid	= next->pid;
  *		__entry->next_prio	= next->prio;
  *	),
diff --git a/include/trace/events/block.h b/include/trace/events/block.h
index 9c97a16850b9..1e3a9ded03bd 100644
--- a/include/trace/events/block.h
+++ b/include/trace/events/block.h
@@ -213,7 +213,7 @@ DECLARE_EVENT_CLASS(block_rq,
 
 		blk_fill_rwbs(__entry->rwbs, rq->cmd_flags);
 		__get_str(cmd)[0] = '\0';
-		memcpy(__entry->comm, current->comm, TASK_COMM_LEN);
+		copy_task_comm(__entry->comm, current, TASK_COMM_LEN);
 	),
 
 	TP_printk("%d,%d %s %u (%s) %llu + %u %s,%u,%u [%s]",
@@ -410,7 +410,7 @@ DECLARE_EVENT_CLASS(block_bio,
 		__entry->sector		= bio->bi_iter.bi_sector;
 		__entry->nr_sector	= bio_sectors(bio);
 		blk_fill_rwbs(__entry->rwbs, bio->bi_opf);
-		memcpy(__entry->comm, current->comm, TASK_COMM_LEN);
+		copy_task_comm(__entry->comm, current, TASK_COMM_LEN);
 	),
 
 	TP_printk("%d,%d %s %llu + %u [%s]",
@@ -493,7 +493,7 @@ TRACE_EVENT(block_plug,
 	),
 
 	TP_fast_assign(
-		memcpy(__entry->comm, current->comm, TASK_COMM_LEN);
+		copy_task_comm(__entry->comm, current, TASK_COMM_LEN);
 	),
 
 	TP_printk("[%s]", __entry->comm)
@@ -512,7 +512,7 @@ DECLARE_EVENT_CLASS(block_unplug,
 
 	TP_fast_assign(
 		__entry->nr_rq = depth;
-		memcpy(__entry->comm, current->comm, TASK_COMM_LEN);
+		copy_task_comm(__entry->comm, current, TASK_COMM_LEN);
 	),
 
 	TP_printk("[%s] %d", __entry->comm, __entry->nr_rq)
@@ -563,7 +563,7 @@ TRACE_EVENT(block_split,
 		__entry->sector		= bio->bi_iter.bi_sector;
 		__entry->new_sector	= new_sector;
 		blk_fill_rwbs(__entry->rwbs, bio->bi_opf);
-		memcpy(__entry->comm, current->comm, TASK_COMM_LEN);
+		copy_task_comm(__entry->comm, current, TASK_COMM_LEN);
 	),
 
 	TP_printk("%d,%d %s %llu / %llu [%s]",
diff --git a/include/trace/events/coredump.h b/include/trace/events/coredump.h
index c7b9c53fc498..fdd20bc46bb0 100644
--- a/include/trace/events/coredump.h
+++ b/include/trace/events/coredump.h
@@ -32,7 +32,7 @@ TRACE_EVENT(coredump,
 
 	TP_fast_assign(
 		__entry->sig = sig;
-		memcpy(__entry->comm, current->comm, TASK_COMM_LEN);
+		copy_task_comm(__entry->comm, current, TASK_COMM_LEN);
 	),
 
 	TP_printk("sig=%d comm=%s",
diff --git a/include/trace/events/f2fs.h b/include/trace/events/f2fs.h
index 270c1a2c24c4..7d22650b4c78 100644
--- a/include/trace/events/f2fs.h
+++ b/include/trace/events/f2fs.h
@@ -2505,7 +2505,7 @@ TRACE_EVENT(f2fs_lock_elapsed_time,
 
 	TP_fast_assign(
 		__entry->dev		= sbi->sb->s_dev;
-		memcpy(__entry->comm, p->comm, TASK_COMM_LEN);
+		copy_task_comm(__entry->comm, p, TASK_COMM_LEN);
 		__entry->pid		= p->pid;
 		__entry->prio		= p->prio;
 		__entry->ioprio_class	= IOPRIO_PRIO_CLASS(ioprio);
@@ -2558,7 +2558,7 @@ DECLARE_EVENT_CLASS(f2fs_priority_update,
 
 	TP_fast_assign(
 		__entry->dev		= sbi->sb->s_dev;
-		memcpy(__entry->comm, p->comm, TASK_COMM_LEN);
+		copy_task_comm(__entry->comm, p, TASK_COMM_LEN);
 		__entry->pid		= p->pid;
 		__entry->lock_name	= lock_name;
 		__entry->is_write	= is_write;
diff --git a/include/trace/events/oom.h b/include/trace/events/oom.h
index 9f0a5d1482c4..8bcdc4ffc8d3 100644
--- a/include/trace/events/oom.h
+++ b/include/trace/events/oom.h
@@ -23,7 +23,7 @@ TRACE_EVENT(oom_score_adj_update,
 
 	TP_fast_assign(
 		__entry->pid = task->pid;
-		memcpy(__entry->comm, task->comm, TASK_COMM_LEN);
+		copy_task_comm(__entry->comm, task, TASK_COMM_LEN);
 		__entry->oom_score_adj = task->signal->oom_score_adj;
 	),
 
diff --git a/include/trace/events/osnoise.h b/include/trace/events/osnoise.h
index 3f4273623801..2cf047bb9fb7 100644
--- a/include/trace/events/osnoise.h
+++ b/include/trace/events/osnoise.h
@@ -116,7 +116,7 @@ TRACE_EVENT(thread_noise,
 	),
 
 	TP_fast_assign(
-		memcpy(__entry->comm, t->comm, TASK_COMM_LEN);
+		copy_task_comm(__entry->comm, t, TASK_COMM_LEN);
 		__entry->pid = t->pid;
 		__entry->start = start;
 		__entry->duration = duration;
diff --git a/include/trace/events/sched.h b/include/trace/events/sched.h
index 535860581f15..afb24e9dac91 100644
--- a/include/trace/events/sched.h
+++ b/include/trace/events/sched.h
@@ -152,7 +152,7 @@ DECLARE_EVENT_CLASS(sched_wakeup_template,
 	),
 
 	TP_fast_assign(
-		memcpy(__entry->comm, p->comm, TASK_COMM_LEN);
+		copy_task_comm(__entry->comm, p, TASK_COMM_LEN);
 		__entry->pid		= p->pid;
 		__entry->prio		= p->prio; /* XXX SCHED_DEADLINE */
 		__entry->target_cpu	= task_cpu(p);
@@ -237,11 +237,11 @@ TRACE_EVENT(sched_switch,
 	),
 
 	TP_fast_assign(
-		memcpy(__entry->prev_comm, prev->comm, TASK_COMM_LEN);
+		copy_task_comm(__entry->prev_comm, prev, TASK_COMM_LEN);
 		__entry->prev_pid	= prev->pid;
 		__entry->prev_prio	= prev->prio;
 		__entry->prev_state	= __trace_sched_switch_state(preempt, prev_state, prev);
-		memcpy(__entry->next_comm, next->comm, TASK_COMM_LEN);
+		copy_task_comm(__entry->next_comm, next, TASK_COMM_LEN);
 		__entry->next_pid	= next->pid;
 		__entry->next_prio	= next->prio;
 		/* XXX SCHED_DEADLINE */
@@ -346,7 +346,7 @@ TRACE_EVENT(sched_process_exit,
 	),
 
 	TP_fast_assign(
-		memcpy(__entry->comm, p->comm, TASK_COMM_LEN);
+		copy_task_comm(__entry->comm, p, TASK_COMM_LEN);
 		__entry->pid		= p->pid;
 		__entry->prio		= p->prio; /* XXX SCHED_DEADLINE */
 		__entry->group_dead	= group_dead;
@@ -787,7 +787,7 @@ TRACE_EVENT(sched_skip_cpuset_numa,
 	),
 
 	TP_fast_assign(
-		memcpy(__entry->comm, tsk->comm, TASK_COMM_LEN);
+		copy_task_comm(__entry->comm, tsk, TASK_COMM_LEN);
 		__entry->pid		 = task_pid_nr(tsk);
 		__entry->tgid		 = task_tgid_nr(tsk);
 		__entry->ngid		 = task_numa_group_id(tsk);
diff --git a/include/trace/events/signal.h b/include/trace/events/signal.h
index 1db7e4b07c01..8fffe6d9bdcc 100644
--- a/include/trace/events/signal.h
+++ b/include/trace/events/signal.h
@@ -67,7 +67,7 @@ TRACE_EVENT(signal_generate,
 	TP_fast_assign(
 		__entry->sig	= sig;
 		TP_STORE_SIGINFO(__entry, info);
-		memcpy(__entry->comm, task->comm, TASK_COMM_LEN);
+		copy_task_comm(__entry->comm, task, TASK_COMM_LEN);
 		__entry->pid	= task->pid;
 		__entry->group	= group;
 		__entry->result	= result;
diff --git a/include/trace/events/task.h b/include/trace/events/task.h
index b9a129eb54d9..62b7df4d22d0 100644
--- a/include/trace/events/task.h
+++ b/include/trace/events/task.h
@@ -21,7 +21,7 @@ TRACE_EVENT(task_newtask,
 
 	TP_fast_assign(
 		__entry->pid = task->pid;
-		memcpy(__entry->comm, task->comm, TASK_COMM_LEN);
+		copy_task_comm(__entry->comm, task, TASK_COMM_LEN);
 		__entry->clone_flags = clone_flags;
 		__entry->oom_score_adj = task->signal->oom_score_adj;
 	),
@@ -46,8 +46,9 @@ TRACE_EVENT(task_rename,
 
 	TP_fast_assign(
 		__entry->pid = task->pid;
-		memcpy(entry->oldcomm, task->comm, TASK_COMM_LEN);
-		strscpy(entry->newcomm, comm, TASK_COMM_LEN);
+		copy_task_comm(entry->oldcomm, task, TASK_COMM_LEN);
+		memcpy(entry->newcomm, comm, TASK_COMM_LEN);
+		entry->newcomm[TASK_COMM_LEN - 1] = '\0';
 		__entry->oom_score_adj = task->signal->oom_score_adj;
 	),
 
diff --git a/kernel/printk/nbcon.c b/kernel/printk/nbcon.c
index 4b03b019cd5e..f4c5ae8a3530 100644
--- a/kernel/printk/nbcon.c
+++ b/kernel/printk/nbcon.c
@@ -952,7 +952,7 @@ static void wctxt_load_execution_ctx(struct nbcon_write_context *wctxt,
 {
 	wctxt->cpu = pmsg->cpu;
 	wctxt->pid = pmsg->pid;
-	memcpy(wctxt->comm, pmsg->comm, sizeof(wctxt->comm));
+	copy_task_comm(wctxt->comm, pmsg, sizeof(wctxt->comm));
 	static_assert(sizeof(wctxt->comm) == sizeof(pmsg->comm));
 }
 #else
diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
index 019b11de262c..ec0c6734bbe1 100644
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -2255,7 +2255,7 @@ static void pmsg_load_execution_ctx(struct printk_message *pmsg,
 {
 	pmsg->cpu = printk_info_get_cpu(info);
 	pmsg->pid = printk_info_get_pid(info);
-	memcpy(pmsg->comm, info->comm, sizeof(pmsg->comm));
+	copy_task_comm(pmsg->comm, info, sizeof(pmsg->comm));
 	static_assert(sizeof(pmsg->comm) == sizeof(info->comm));
 }
 #else

-- 
2.55.0