Re: [PATCH v2 15/41] SUNRPC: Enable rpcsec_gss_krb5.ko to be built without CRYPTO_DES

[Chuck Lever III]

> On Mar 6, 2023, at 3:16 AM, Geert Uytterhoeven <geert@xxxxxxxxxxxxxx> wrote:
> 
> 	Hi Chuck,
> 
> On Sun, 15 Jan 2023, Chuck Lever wrote:
>> From: Chuck Lever <chuck.lever@xxxxxxxxxx>
>> 
>> Because the DES block cipher has been deprecated by Internet
>> standard, highly secure configurations might require that DES
>> support be blacklisted or not installed. NFS Kerberos should still
>> be able to work correctly with only the AES-based enctypes in that
>> situation.
>> 
>> Also note that MIT Kerberos has begun a deprecation process for DES
>> encryption types. Their README for 1.19.3 states:
>> 
>>> Beginning with the krb5-1.19 release, a warning will be issued
>>> if initial credentials are acquired using the des3-cbc-sha1
>>> encryption type.  In future releases, this encryption type will
>>> be disabled by default and eventually removed.
>>> 
>>> Beginning with the krb5-1.18 release, single-DES encryption
>>> types have been removed.
>> 
>> Aside from the CONFIG option name change, there are two important
>> policy changes:
>> 
>> 1. The 'insecure enctype' group is now disabled by default.
>>  Distributors have to take action to enable support for deprecated
>>  enctypes. Implementation of these enctypes will be removed in a
>>  future kernel release.
>> 
>> 2. des3-cbc-sha1 is now considered part of the 'insecure enctype'
>>  group, having been deprecated by RFC 8429, and is thus disabled
>>  by default
>> 
>> After this patch is applied, SunRPC support can be built with
>> Kerberos 5 support but without CRYPTO_DES enabled in the kernel.
>> And, when these enctypes are disabled, the Linux kernel's SunRPC
>> RPCSEC GSS implementation fully complies with BCP 179 / RFC 6649
>> and BCP 218 / RFC 8429.
>> 
>> Tested-by: Scott Mayhew <smayhew@xxxxxxxxxx>
>> Signed-off-by: Chuck Lever <chuck.lever@xxxxxxxxxx>
> 
> Thanks for your patch, which is now commit dfe9a123451a6e73 ("SUNRPC:
> Enable rpcsec_gss_krb5.ko to be built without CRYPTO_DES") in v6.3-rc1.
> 
>> --- a/net/sunrpc/Kconfig
>> +++ b/net/sunrpc/Kconfig
>> @@ -19,10 +19,10 @@ config SUNRPC_SWAP
>> config RPCSEC_GSS_KRB5
>> 	tristate "Secure RPC: Kerberos V mechanism"
>> 	depends on SUNRPC && CRYPTO
>> -	depends on CRYPTO_MD5 && CRYPTO_DES && CRYPTO_CBC && CRYPTO_CTS
>> -	depends on CRYPTO_ECB && CRYPTO_HMAC && CRYPTO_SHA1 && CRYPTO_AES
>> 	default y
>> 	select SUNRPC_GSS
>> +	select CRYPTO_SKCIPHER
>> +	select CRYPTO_HASH
>> 	help
>> 	  Choose Y here to enable Secure RPC using the Kerberos version 5
>> 	  GSS-API mechanism (RFC 1964).
> 
> While updating my defconfigs for v6.3-rc1, I noticed this change has an
> interesting side-effect: if any of the CRYPTO_* algorithms were modular
> before, RPCSEC_GSS_KRB5 was modular, too.
> After this change, RPCSEC_GSS_KRB5 is promoted to builtin.

I'm not following. Which CRYPTO_ options trigger the behavior?
On my test system, CONFIG_RPCSEC_GSS_KRB5=m and the CRYPTO stuff
is all =y.


> This is not necessarily bad in-se, but you might want to be aware of it,
> and perhaps change the "default y".

Well that might be there to address the need for GSS to be
enabled if NFSv4 support is built. See commit df486a25900f
("NFS: Fix the selection of security flavours in Kconfig")

I'm not claiming I understand exactly how that fix works.

--
Chuck Lever