[patch 13/55] fs/exec: replace strncpy with strscpy_pad in __get_task_comm

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From: Yafang Shao <laoar.shao@xxxxxxxxx>
Subject: fs/exec: replace strncpy with strscpy_pad in __get_task_comm

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 and zero padded.

Link: https://lkml.kernel.org/r/20211120112738.45980-3-laoar.shao@xxxxxxxxx
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>
Reviewed-by: David Hildenbrand <david@xxxxxxxxxx>
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>
Cc: Andrii Nakryiko <andrii@xxxxxxxxxx>
Cc: Dennis Dalessandro <dennis.dalessandro@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---

 fs/exec.c |    3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

--- a/fs/exec.c~fs-exec-replace-strncpy-with-strscpy_pad-in-__get_task_comm
+++ a/fs/exec.c
@@ -1207,7 +1207,8 @@ static int unshare_sighand(struct task_s
 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;
 }
_



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