linux-hardening - Re: [PATCH v3] NFSD: Remove open coding of string copy

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Date:   Tue, 16 May 2023 14:10:42 +0000
From:   Chuck Lever III <chuck.lever@...cle.com>
To:     David Laight <David.Laight@...LAB.COM>
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 v3] NFSD: Remove open coding of string copy



> On May 16, 2023, at 5:33 AM, David Laight <David.Laight@...LAB.COM> wrote:
> 
> From: Azeem Shaikh
>> Sent: 15 May 2023 03:41
>> 
>> Instead of open coding a __dynamic_array(), use the __string() and
>> __assign_str() helper macros that exist for this kind of use case.
> 
> Is this actually a dynamic array, or just a char[8] ?
> On 64 bit copying a short fixed-length string is far better
> than any kind of dynamic sized allocation.

I'd prefer to use a string helper, since the netid is a string,
and this documents the data type better and it is not subject
to sudden breakage if someone creates a standard netid longer
than 8 characters.

The nfsd_cb_setup tracepoint is not in a performance-sensitive
path.

In addition, trace consumers should be able to count on the
string helpers to perform memory copies without overrunning
either the source or destination buffers... one less source
of error.


> David
> 
>> 
>> Part of an effort to remove deprecated strlcpy() [1] completely from the
>> kernel[2].
>> 
>> [1] https://www.kernel.org/doc/html/latest/process/deprecated.html#strlcpy
>> [2] https://github.com/KSPP/linux/issues/89
>> 
>> Fixes: 3c92fba557c6 ("NFSD: Enhance the nfsd_cb_setup tracepoint")
>> Signed-off-by: Azeem Shaikh <azeemshaikh38@...il.com>
>> ---
>> fs/nfsd/trace.h |    6 +++---
>> 1 file changed, 3 insertions(+), 3 deletions(-)
>> 
>> diff --git a/fs/nfsd/trace.h b/fs/nfsd/trace.h
>> index 4183819ea082..72a906a053dc 100644
>> --- a/fs/nfsd/trace.h
>> +++ b/fs/nfsd/trace.h
>> @@ -1365,19 +1365,19 @@ TRACE_EVENT(nfsd_cb_setup,
>> __field(u32, cl_id)
>> __field(unsigned long, authflavor)
>> __sockaddr(addr, clp->cl_cb_conn.cb_addrlen)
>> - __array(unsigned char, netid, 8)
>> + __string(netid, netid)
>> ),
>> 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));
>> + __assign_str(netid, netid);
>> __entry->authflavor = authflavor;
>> __assign_sockaddr(addr, &clp->cl_cb_conn.cb_addr,
>>   clp->cl_cb_conn.cb_addrlen)
>> ),
>> TP_printk("addr=%pISpc client %08x:%08x proto=%s flavor=%s",
>> __get_sockaddr(addr), __entry->cl_boot, __entry->cl_id,
>> - __entry->netid, show_nfsd_authflavor(__entry->authflavor))
>> + __get_str(netid), show_nfsd_authflavor(__entry->authflavor))
>> );
>> 
>> TRACE_EVENT(nfsd_cb_setup_err,
>> --
>> 2.40.1.606.ga4b1b128d6-goog
>> 
> 
> -
> Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK
> Registration No: 1397386 (Wales)


--
Chuck Lever