[PATCH 2/7] fs/exec: make __get_task_comm always get a nul terminated string

[Yafang Shao]

If the dest buffer size is smaller than sizeof(tsk->comm), the buffer
will be without null ternimator, that may cause problem. Using
strscpy_pad() instead of strncpy() in __get_task_comm() can make the string
always nul ternimated.

Suggested-by: Kees Cook <keescook@xxxxxxxxxxxx>
Suggested-by: Steven Rostedt <rostedt@xxxxxxxxxxx>
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>
---
 fs/exec.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/fs/exec.c b/fs/exec.c
index 404156b5b314..013b707d995d 100644
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -1209,7 +1209,8 @@ static int unshare_sighand(struct task_struct *me)
 char *__get_task_comm(char *buf, size_t buf_size, struct task_struct *tsk)
 {
 	task_lock(tsk);
-	strncpy(buf, tsk->comm, buf_size);
+	/* Always NUL terminated and zero-padded */
+	strscpy_pad(buf, tsk->comm, buf_size);
 	task_unlock(tsk);
 	return buf;
 }
-- 
2.17.1