linux-hardening - Re: [PATCH] tracing/boot: Replace strlcpy with strscpy

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Date:   Wed, 14 Jun 2023 10:13:30 -0700
From:   Eric Biggers <ebiggers@...nel.org>
To:     Azeem Shaikh <azeemshaikh38@...il.com>
Cc:     Kees Cook <keescook@...omium.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        linux-hardening@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-trace-kernel@...r.kernel.org
Subject: Re: [PATCH] tracing/boot: Replace strlcpy with strscpy

On Wed, Jun 14, 2023 at 10:01:57AM -0400, Azeem Shaikh wrote:
> On Tue, Jun 13, 2023 at 3:27 PM Kees Cook <keescook@...omium.org> wrote:
> >
> > On Tue, Jun 13, 2023 at 12:41:25AM +0000, Azeem Shaikh wrote:
> > > strlcpy() reads the entire source buffer first.
> > > This read may exceed the destination size limit.
> > > This is both inefficient and can lead to linear read
> > > overflows if a source string is not NUL-terminated [1].
> > > In an effort to remove strlcpy() completely [2], replace
> > > strlcpy() here with strscpy().
> > >
> > > Direct replacement is safe here since return value of -E2BIG
> > > is used to check for truncation instead of sizeof(dest).
> >
> > This looks technically correct, but I wonder if "< 0" is a better test?
> 
> Agreed. "< 0" might more generically represent -errno. Happy to send
> over a v2 if you prefer that instead of sticking with this patch.

Please go with "< 0", since it's easier to read and less error-prone.  (It would
be easy to mistype -E2BIG as -EFBIG, or E2BIG, for example...)

- Eric