linux-kernel - Re: [PATCH] SUNRPC: Replace strlcpy with strscpy

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Message-ID: <B3AC0B67-1629-44AC-8015-B28F020B018C@oracle.com>
Date:   Tue, 13 Jun 2023 19:43:44 +0000
From:   Chuck Lever III <chuck.lever@...cle.com>
To:     Kees Cook <keescook@...omium.org>
CC:     Azeem Shaikh <azeemshaikh38@...il.com>,
        Jeff Layton <jlayton@...nel.org>,
        "linux-hardening@...r.kernel.org" <linux-hardening@...r.kernel.org>,
        Neil Brown <neilb@...e.de>,
        Olga Kornievskaia <kolga@...app.com>,
        Dai Ngo <dai.ngo@...cle.com>, Tom Talpey <tom@...pey.com>,
        Linux NFS Mailing List <linux-nfs@...r.kernel.org>,
        open list <linux-kernel@...r.kernel.org>,
        Trond Myklebust <trond.myklebust@...merspace.com>,
        Anna Schumaker <anna@...nel.org>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: Re: [PATCH] SUNRPC: Replace strlcpy with strscpy



> On Jun 13, 2023, at 3:42 PM, Kees Cook <keescook@...omium.org> wrote:
> 
> On Tue, Jun 13, 2023 at 02:18:06PM +0000, Chuck Lever III wrote:
>> 
>> 
>>> On Jun 12, 2023, at 8:40 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().
>> 
>> Using sprintf() seems cleaner to me: it would get rid of
>> the undocumented naked integer. Would that work for you?
> 
> This is changing the "get" routine for reporting module parameters out
> of /sys. I think the right choice here is sysfs_emit(), as it performs
> the size tracking correctly. (Even the "default" sprintf() call should
> be replaced too, IMO.)

Agreed, that's even better.


>>> Direct replacement is safe here since the getter in kernel_params_ops
>>> handles -errorno return [3].
>> 
>> s/errorno/errno/
>> 
>> 
>>> [1] https://www.kernel.org/doc/html/latest/process/deprecated.html#strlcpy
>>> [2] https://github.com/KSPP/linux/issues/89
>>> [3] https://elixir.bootlin.com/linux/v6.4-rc6/source/include/linux/moduleparam.h#L52
>>> 
>>> Signed-off-by: Azeem Shaikh <azeemshaikh38@...il.com>
>>> ---
>>> net/sunrpc/svc.c |    8 ++++----
>>> 1 file changed, 4 insertions(+), 4 deletions(-)
>>> 
>>> diff --git a/net/sunrpc/svc.c b/net/sunrpc/svc.c
>>> index e6d4cec61e47..e5f379c4fdb3 100644
>>> --- a/net/sunrpc/svc.c
>>> +++ b/net/sunrpc/svc.c
>>> @@ -109,13 +109,13 @@ param_get_pool_mode(char *buf, const struct kernel_param *kp)
>>> switch (*ip)
>>> {
>>> case SVC_POOL_AUTO:
>>> - return strlcpy(buf, "auto\n", 20);
>>> + return strscpy(buf, "auto\n", 20);
> 
> e.g.
> return sysfs_emit(buf, "auto\n");
> ...
> 
>>> case SVC_POOL_GLOBAL:
>>> - return strlcpy(buf, "global\n", 20);
>>> + return strscpy(buf, "global\n", 20);
>>> case SVC_POOL_PERCPU:
>>> - return strlcpy(buf, "percpu\n", 20);
>>> + return strscpy(buf, "percpu\n", 20);
>>> case SVC_POOL_PERNODE:
>>> - return strlcpy(buf, "pernode\n", 20);
>>> + return strscpy(buf, "pernode\n", 20);
>>> default:
>>> return sprintf(buf, "%d\n", *ip);
> 
> and:
> 
> return sysfs_emit(buf, "%d\n", *ip);
> 
> 
> -Kees
> 
> -- 
> Kees Cook


--
Chuck Lever