On Tue, Oct 26, 2021 at 5:08 AM Kees Cook [off-list ref] wrote:

On Mon, Oct 25, 2021 at 08:33:05AM +0000, Yafang Shao wrote:

quoted

If the dest buffer size is smaller than sizeof(tsk->comm), the buffer
will be without null ternimator, that may cause problem. We can make sure
the buffer size not smaller than comm at the callsite to avoid that
problem, but there may be callsite that we can't easily change.

Using strscpy_pad() instead of strncpy() in __get_task_comm() can make
the string always nul ternimated.

Suggested-by: Kees Cook <redacted>
Suggested-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Yafang Shao <redacted>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Arnaldo Carvalho de Melo <redacted>
Cc: Andrii Nakryiko <redacted>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Kees Cook <redacted>
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 404156b5b314..bf2a7a91eeea 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);
+     /* The copied value is always null terminated */

This may could say "always NUL terminated and zero-padded"

Sure. I will change it.

quoted

+     strscpy_pad(buf, tsk->comm, buf_size);
      task_unlock(tsk);
      return buf;
 }
--
2.17.1

But for the replacement with strscpy_pad(), yes please:

Reviewed-by: Kees Cook <redacted>


--
Kees Cook

-- 
Thanks
Yafang