From:   Yafang Shao <laoar.shao@gmail.com>
To:     akpm@linux-foundation.org
Cc:     netdev@vger.kernel.org, bpf@vger.kernel.org,
        linux-perf-users@vger.kernel.org, linux-fsdevel@vger.kernel.org,
        linux-mm@kvack.org, linux-kernel@vger.kernel.org,
        oliver.sang@intel.com, lkp@intel.com,
        Yafang Shao <laoar.shao@gmail.com>,
        Kees Cook <keescook@chromium.org>,
        Steven Rostedt <rostedt@goodmis.org>,
        David Hildenbrand <david@redhat.com>,
        Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
        Arnaldo Carvalho de Melo <arnaldo.melo@gmail.com>,
        Alexei Starovoitov <alexei.starovoitov@gmail.com>,
        Andrii Nakryiko <andrii.nakryiko@gmail.com>,
        Michal Miroslaw <mirq-linux@rere.qmqm.pl>,
        Peter Zijlstra <peterz@infradead.org>,
        Matthew Wilcox <willy@infradead.org>,
        Al Viro <viro@zeniv.linux.org.uk>,
        Petr Mladek <pmladek@suse.com>
Subject: [PATCH v2 2/7] fs/exec: replace strncpy with strscpy_pad in __get_task_comm
Date:   Sat, 20 Nov 2021 11:27:33 +0000
Message-Id: <20211120112738.45980-3-laoar.shao@gmail.com>
In-Reply-To: <20211120112738.45980-1-laoar.shao@gmail.com>
References: <20211120112738.45980-1-laoar.shao@gmail.com>
MIME-Version: 1.0
Content-Transfer-Encoding: 8bit
Precedence: bulk

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.

Suggested-by: Kees Cook <keescook@chromium.org>
Suggested-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Yafang Shao <laoar.shao@gmail.com>
Reviewed-by: Kees Cook <keescook@chromium.org>
Reviewed-by: David Hildenbrand <david@redhat.com>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Arnaldo Carvalho de Melo <arnaldo.melo@gmail.com>
Cc: Alexei Starovoitov <alexei.starovoitov@gmail.com>
Cc: Andrii Nakryiko <andrii.nakryiko@gmail.com>
Cc: Michal Miroslaw <mirq-linux@rere.qmqm.pl>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: David Hildenbrand <david@redhat.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Kees Cook <keescook@chromium.org>
Cc: Petr Mladek <pmladek@suse.com>
---
 fs/exec.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/fs/exec.c b/fs/exec.c
index 51d3cb4e3cdf..fa142638b191 100644
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -1207,7 +1207,8 @@ 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