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

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Message-Id: <20211108083840.4627-3-laoar.shao@gmail.com>
Date:   Mon,  8 Nov 2021 08:38:35 +0000
From:   Yafang Shao <laoar.shao@...il.com>
To:     akpm@...ux-foundation.org
Cc:     netdev@...r.kernel.org, bpf@...r.kernel.org,
        linux-perf-users@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        oliver.sang@...el.com, lkp@...el.com,
        Yafang Shao <laoar.shao@...il.com>,
        Kees Cook <keescook@...omium.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        Arnaldo Carvalho de Melo <arnaldo.melo@...il.com>,
        Alexei Starovoitov <alexei.starovoitov@...il.com>,
        Andrii Nakryiko <andrii.nakryiko@...il.com>,
        Michal Miroslaw <mirq-linux@...e.qmqm.pl>,
        Peter Zijlstra <peterz@...radead.org>,
        Matthew Wilcox <willy@...radead.org>,
        David Hildenbrand <david@...hat.com>,
        Al Viro <viro@...iv.linux.org.uk>,
        Petr Mladek <pmladek@...e.com>
Subject: [PATCH 2/7] fs/exec: make __get_task_comm always get a nul terminated string

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@...omium.org>
Suggested-by: Steven Rostedt <rostedt@...dmis.org>
Signed-off-by: Yafang Shao <laoar.shao@...il.com>
Reviewed-by: Kees Cook <keescook@...omium.org>
Cc: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
Cc: Arnaldo Carvalho de Melo <arnaldo.melo@...il.com>
Cc: Alexei Starovoitov <alexei.starovoitov@...il.com>
Cc: Andrii Nakryiko <andrii.nakryiko@...il.com>
Cc: Michal Miroslaw <mirq-linux@...e.qmqm.pl>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Steven Rostedt <rostedt@...dmis.org>
Cc: Matthew Wilcox <willy@...radead.org>
Cc: David Hildenbrand <david@...hat.com>
Cc: Al Viro <viro@...iv.linux.org.uk>
Cc: Kees Cook <keescook@...omium.org>
Cc: Petr Mladek <pmladek@...e.com>
---
 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