linux-hardening - Re: [PATCH] NFSD: Replace all non-returning strlcpy with strscpy

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Date:   Thu, 11 May 2023 09:32:31 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Chuck Lever III <chuck.lever@...cle.com>,
        Steven Rostedt <rostedt@...dmis.org>
Cc:     Azeem Shaikh <azeemshaikh38@...il.com>,
        Jeff Layton <jlayton@...nel.org>,
        "linux-hardening@...r.kernel.org" <linux-hardening@...r.kernel.org>,
        Linux NFS Mailing List <linux-nfs@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] NFSD: Replace all non-returning strlcpy with strscpy

On Thu, May 11, 2023 at 02:47:54PM +0000, Chuck Lever III wrote:
> Hello Azeem -
> 
> > On May 10, 2023, at 3:09 PM, Azeem Shaikh <azeemshaikh38@...il.com> 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().
> > No return values were used, so direct replacement is safe.
> 
> Actually netid should use the __string() and __assign_str()
> macros rather than open-coding a string copy, I think.

Ah, hm, yeah, this is tracing wrappers.

Steve, is there a reason __assign_str() is using "strcpy" and not
strscpy()?

> Fixes: 3c92fba557c6 ("NFSD: Enhance the nfsd_cb_setup tracepoint")

Yeah, that works. I was on the fence about adding Fixes for these kinds
of refactoring. Like, it's not really _broken_; we're just trying to
remove the API.

> > Signed-off-by: Azeem Shaikh <azeemshaikh38@...il.com>
> > ---
> > fs/nfsd/trace.h |    2 +-
> > 1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > diff --git a/fs/nfsd/trace.h b/fs/nfsd/trace.h
> > index 4183819ea082..9b32cda54808 100644
> > --- a/fs/nfsd/trace.h
> > +++ b/fs/nfsd/trace.h
> > @@ -1370,7 +1370,7 @@ TRACE_EVENT(nfsd_cb_setup,
> > TP_fast_assign(
> > __entry->cl_boot = clp->cl_clientid.cl_boot;
> > __entry->cl_id = clp->cl_clientid.cl_id;
> > - strlcpy(__entry->netid, netid, sizeof(__entry->netid));
> > + strscpy(__entry->netid, netid, sizeof(__entry->netid));
> > __entry->authflavor = authflavor;
> > __assign_sockaddr(addr, &clp->cl_cb_conn.cb_addr,
> >  clp->cl_cb_conn.cb_addrlen)

Leaving code context for Steve to see...

-- 
Kees Cook