linux-kernel - Re: [PATCH] IB/hfi1: replace deprecated strncpy

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Message-ID: <202309232019.BE78A9C0@keescook>
Date:   Sat, 23 Sep 2023 20:20:54 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Dean Luick <dean.luick@...nelisnetworks.com>
Cc:     Leon Romanovsky <leon@...nel.org>,
        Dennis Dalessandro <dennis.dalessandro@...nelisnetworks.com>,
        Jason Gunthorpe <jgg@...pe.ca>,
        Justin Stitt <justinstitt@...gle.com>,
        linux-rdma@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-hardening@...r.kernel.org
Subject: Re: [PATCH] IB/hfi1: replace deprecated strncpy

On Fri, Sep 22, 2023 at 09:25:39AM -0500, Dean Luick wrote:
> On 9/22/2023 5:29 AM, Leon Romanovsky wrote:
> >
> > On Thu, 21 Sep 2023 07:17:47 +0000, Justin Stitt wrote:
> >> `strncpy` is deprecated for use on NUL-terminated destination strings
> >> [1] and as such we should prefer more robust and less ambiguous string
> >> interfaces.
> >>
> >> We see that `buf` is expected to be NUL-terminated based on it's use
> >> within a trace event wherein `is_misc_err_name` and `is_various_name`
> >> map to `is_name` through `is_table`:
> >> | TRACE_EVENT(hfi1_interrupt,
> >> |        TP_PROTO(struct hfi1_devdata *dd, const struct is_table *is_entry,
> >> |                 int src),
> >> |        TP_ARGS(dd, is_entry, src),
> >> |        TP_STRUCT__entry(DD_DEV_ENTRY(dd)
> >> |                         __array(char, buf, 64)
> >> |                         __field(int, src)
> >> |                         ),
> >> |        TP_fast_assign(DD_DEV_ASSIGN(dd);
> >> |                       is_entry->is_name(__entry->buf, 64,
> >> |                                         src - is_entry->start);
> >> |                       __entry->src = src;
> >> |                       ),
> >> |        TP_printk("[%s] source: %s [%d]", __get_str(dev), __entry->buf,
> >> |                  __entry->src)
> >> | );
> >>
> >> [...]
> >
> > Applied, thanks!
> 
> It is unfortunate that this and the qib patch was accepted so quickly.  The replacement is functionally correct.  However, I was going to suggest using strscpy() since the return value is never looked at and all use cases only require a NUL-terminated string.  Padding is not needed.

Is the trace buffer already guaranteed to be zeroed? Since this is
defined as a fixed-size string in the buffer, it made sense to me to be
sure that the unused bytes were 0 before copying them to userspace.

-Kees

> 
> >
> > [1/1] IB/hfi1: replace deprecated strncpy
> >       https://git.kernel.org/rdma/rdma/c/c2d0c5b28a77d5
> >
> > Best regards,
> 
> External recipient

-- 
Kees Cook