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From:   Olga Kornievskaia <olga.kornievskaia@gmail.com>
Date:   Thu, 26 Mar 2020 08:04:13 -0400
Message-ID: <CAN-5tyEDRQZX-saVrbfn7G7pzmSOyROipEzxjVPxF1WV8rK+vg@mail.gmail.com>
Subject: Re: [PATCH 1/1] SUNRPC: fix krb5p mount to provide large enough
 buffer in rq_rcvsize
To:     Chuck Lever <chuck.lever@oracle.com>
Cc:     Trond Myklebust <trond.myklebust@hammerspace.com>,
        Anna Schumaker <anna.schumaker@netapp.com>,
        Linux NFS Mailing List <linux-nfs@vger.kernel.org>
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On Wed, Mar 25, 2020 at 5:34 PM Chuck Lever <chuck.lever@oracle.com> wrote:
>
>
>
> > On Mar 25, 2020, at 5:01 PM, Olga Kornievskaia <olga.kornievskaia@gmail.com> wrote:
> >
> > From: Olga Kornievskaia <kolga@netapp.com>
> >
> > 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.
> >
> > Since 5.1, v3 mount with sec=krb5p fails against an Ontap server
> > because client's receive buffer it too small.
> >
> > For gss krb5p, we need to account for the mic token in the verifier,
> > and the wrap token in the wrap token.
> >
> > 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.
> >
> > that's 16bytes (GSS_KRB5_TOK_HDR_LEN) + chksum
> >
> > 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.
> >
> > Also 16bytes of header (GSS_KRB5_TOK_HDR_LEN), encrypted data, and cksum
> > (other things like padding)
> >
> > RFC 3961 defines known cksum sizes:
> > Checksum type              sumtype        checksum         section or
> >                                value            size         reference
> >   ---------------------------------------------------------------------
> >   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]
> >
> > Linux kernel now mainly supports type 15,16 so max cksum size is 20bytes.
> > (GSS_KRB5_MAX_CKSUM_LEN)
> >
> > 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).
> >
> > 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(-)
> >
> > 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)
>
> GSS_KRB5_MAX_SLACK_NEEDED is already in bytes. Shouldn't need the "<< 2" here.


Ok yes just for my own understanding I convinced myself that indeed
"<<2" is not needed here because clnt.c will do rq_rcvsize is <<=2.

Now question: Do I even need to introduce GSS_RES_SLACK at all or
perhaps just use GSS_KRB5_MAX_SLACK_NEEDED to initialize?

> > 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 = &gss_auth->rpc_auth;
> >       auth->au_cslack = GSS_CRED_SLACK >> 2;
> > -     auth->au_rslack = GSS_VERF_SLACK >> 2;
> > +     auth->au_rslack = GSS_RESP_SLACK >> 2;
> >       auth->au_verfsize = GSS_VERF_SLACK >> 2;
> >       auth->au_ralign = GSS_VERF_SLACK >> 2;
> >       auth->au_flags = 0;
> > --
> > 1.8.3.1
> >
>
> --
> Chuck Lever
>
>
>