Received-SPF: pass (google.com: best guess record for domain of linux-nfs-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
Content-Type: text/plain;
        charset=us-ascii
Mime-Version: 1.0 (Mac OS X Mail 12.4 \(3445.104.11\))
Subject: Re: [PATCH 1/1] SUNRPC: fix krb5p mount to provide large enough
 buffer in rq_rcvsize
From:   Chuck Lever <chuck.lever@oracle.com>
In-Reply-To: <7363e7b550dc5adad3f00fb84d9586764b8ec4fb.camel@hammerspace.com>
Date:   Wed, 25 Mar 2020 17:43:47 -0400
Cc:     Anna Schumaker <anna.schumaker@netapp.com>,
        Olga Kornievskaia <olga.kornievskaia@gmail.com>,
        Linux NFS Mailing List <linux-nfs@vger.kernel.org>
Content-Transfer-Encoding: quoted-printable
Message-Id: <8A8EC7E8-9EB6-49DA-8393-241B4977E67E@oracle.com>
References: <20200325210136.2826-1-olga.kornievskaia@gmail.com>
 <7363e7b550dc5adad3f00fb84d9586764b8ec4fb.camel@hammerspace.com>
To:     Trond Myklebust <trondmy@hammerspace.com>
Sender: linux-nfs-owner@vger.kernel.org
Precedence: bulk


> On Mar 25, 2020, at 5:33 PM, Trond Myklebust <trondmy@hammerspace.com> =
wrote:
>=20
> Hi Olga,
>=20
> On Wed, 2020-03-25 at 17:01 -0400, Olga Kornievskaia wrote:
>> From: Olga Kornievskaia <kolga@netapp.com>
>>=20
>> Ever since commit 2c94b8eca1a2 ("SUNRPC: Use au_rslack when computing
>> reply buffer size"). It changed how "req->rq_rcvsize" is calculated.
>> It
>> used to use au_cslack value which was nice and large and changed it
>> to
>> au_rslack value which turns out to be too small.
>>=20
>> Since 5.1, v3 mount with sec=3Dkrb5p fails against an Ontap server
>> because client's receive buffer it too small.
>>=20
>> For gss krb5p, we need to account for the mic token in the verifier,
>> and the wrap token in the wrap token.
>>=20
>> RFC 4121 defines:
>> mic token
>> Octet no   Name        Description
>>         ----------------------------------------------------------
>> ----
>>         0..1     TOK_ID     Identification field.  Tokens emitted by
>>                             GSS_GetMIC() contain the hex value 04 04
>>                             expressed in big-endian order in this
>>                             field.
>>         2        Flags      Attributes field, as described in
>> section
>>                             4.2.2.
>>         3..7     Filler     Contains five octets of hex value FF.
>>         8..15    SND_SEQ    Sequence number field in clear text,
>>                             expressed in big-endian order.
>>         16..last SGN_CKSUM  Checksum of the "to-be-signed" data and
>>                             octet 0..15, as described in section
>> 4.2.4.
>>=20
>> that's 16bytes (GSS_KRB5_TOK_HDR_LEN) + chksum
>>=20
>> wrap token
>> Octet no   Name        Description
>>         ----------------------------------------------------------
>> ----
>>          0..1     TOK_ID    Identification field.  Tokens emitted by
>>                             GSS_Wrap() contain the hex value 05 04
>>                             expressed in big-endian order in this
>>                             field.
>>          2        Flags     Attributes field, as described in
>> section
>>                             4.2.2.
>>          3        Filler    Contains the hex value FF.
>>          4..5     EC        Contains the "extra count" field, in
>> big-
>>                             endian order as described in section
>> 4.2.3.
>>          6..7     RRC       Contains the "right rotation count" in
>> big-
>>                             endian order, as described in section
>>                             4.2.5.
>>          8..15    SND_SEQ   Sequence number field in clear text,
>>                             expressed in big-endian order.
>>          16..last Data      Encrypted data for Wrap tokens with
>>                             confidentiality, or plaintext data
>> followed
>>                             by the checksum for Wrap tokens without
>>                             confidentiality, as described in section
>>                             4.2.4.
>>=20
>> Also 16bytes of header (GSS_KRB5_TOK_HDR_LEN), encrypted data, and
>> cksum
>> (other things like padding)
>>=20
>> RFC 3961 defines known cksum sizes:
>> Checksum type              sumtype        checksum         section or
>>                                value            size         referen
>> ce
>>   ----------------------------------------------------------------
>> -----
>>   CRC32                            1               4           6.1.3
>>   rsa-md4                          2              16           6.1.2
>>   rsa-md4-des                      3              24           6.2.5
>>   des-mac                          4              16           6.2.7
>>   des-mac-k                        5               8           6.2.8
>>   rsa-md4-des-k                    6              16           6.2.6
>>   rsa-md5                          7              16           6.1.1
>>   rsa-md5-des                      8              24           6.2.4
>>   rsa-md5-des3                     9              24             ??
>>   sha1 (unkeyed)                  10              20             ??
>>   hmac-sha1-des3-kd               12              20            6.3
>>   hmac-sha1-des3                  13              20             ??
>>   sha1 (unkeyed)                  14              20             ??
>>   hmac-sha1-96-aes128             15              20         [KRB5-
>> AES]
>>   hmac-sha1-96-aes256             16              20         [KRB5-
>> AES]
>>   [reserved]                  0x8003               ?         [GSS-
>> KRB5]
>>=20
>> Linux kernel now mainly supports type 15,16 so max cksum size is
>> 20bytes.
>> (GSS_KRB5_MAX_CKSUM_LEN)
>>=20
>> Re-use already existing define of GSS_KRB5_MAX_SLACK_NEEDED that's
>> used
>> for encoding the gss_wrap tokens (same tokens are used in reply).
>>=20
>> Fixes: 2c94b8eca1a2 ("SUNRPC: Use au_rslack when computing reply
>> buffer size")
>> Signed-off-by: Olga Kornievskaia <kolga@netapp.com>
>> ---
>> net/sunrpc/auth_gss/auth_gss.c | 5 ++++-
>> 1 file changed, 4 insertions(+), 1 deletion(-)
>>=20
>> diff --git a/net/sunrpc/auth_gss/auth_gss.c
>> b/net/sunrpc/auth_gss/auth_gss.c
>> index 24ca861..5a733a6 100644
>> --- a/net/sunrpc/auth_gss/auth_gss.c
>> +++ b/net/sunrpc/auth_gss/auth_gss.c
>> @@ -20,6 +20,7 @@
>> #include <linux/sunrpc/clnt.h>
>> #include <linux/sunrpc/auth.h>
>> #include <linux/sunrpc/auth_gss.h>
>> +#include <linux/sunrpc/gss_krb5.h>
>> #include <linux/sunrpc/svcauth_gss.h>
>> #include <linux/sunrpc/gss_err.h>
>> #include <linux/workqueue.h>
>> @@ -51,6 +52,8 @@
>> /* length of a krb5 verifier (48), plus data added before arguments
>> when
>>  * using integrity (two 4-byte integers): */
>> #define GSS_VERF_SLACK		100
>> +/* covers lengths of gss_unwrap() extra kerberos mic and wrap token
>> */
>> +#define GSS_RESP_SLACK		(GSS_KRB5_MAX_SLACK_NEEDED <<
>> 2)
>>=20
>> static DEFINE_HASHTABLE(gss_auth_hash_table, 4);
>> static DEFINE_SPINLOCK(gss_auth_hash_lock);
>> @@ -1050,7 +1053,7 @@ static void gss_pipe_free(struct gss_pipe *p)
>> 		goto err_put_mech;
>> 	auth =3D &gss_auth->rpc_auth;
>> 	auth->au_cslack =3D GSS_CRED_SLACK >> 2;
>> -	auth->au_rslack =3D GSS_VERF_SLACK >> 2;
>> +	auth->au_rslack =3D GSS_RESP_SLACK >> 2;
>> 	auth->au_verfsize =3D GSS_VERF_SLACK >> 2;
>> 	auth->au_ralign =3D GSS_VERF_SLACK >> 2;
>> 	auth->au_flags =3D 0;
>=20
> Is this a sufficient fix, though? It looks to me as if the above is
> just an initial value that gets adjusted on the fly in
> gss_unwrap_resp_priv():
>=20
>        auth->au_rslack =3D auth->au_verfsize + 2 +
>                          XDR_QUADLEN(savedlen - rcv_buf->len);
>        auth->au_ralign =3D auth->au_verfsize + 2 +
>                          XDR_QUADLEN(savedlen - rcv_buf->len);

That's correct. The GSS_*_SLACK value is a _sz value that is
the largest possible expected size of the extra GSS data.


> My questions would be
>=20
> - Are we sure that the above calculation (in gss_unwrap_resp_priv()) =
is
> correct?

Yes, this is the correct computation.

We know this because if the initial au_rslack value is large
enough, then subsequent Replies have the correct amount of buffer
space and always succeed.


> - Are we sure that the above calculation always gives the same answer
> over time? We probably should not store a value that keeps changing.

It does not change after the first Reply. au_rslack is typically
adjusted downwards from the initial value based on the size of the
first received Reply.

Not setting these variables after the first Reply has been received
would be a minor optimization that could be done after Olga's fix.

--
Chuck Lever