Re: [PATCH 1/1] SUNRPC: fix krb5p mount to provide large enough buffer in rq_rcvsize

[Chuck Lever <chuck.lever@oracle.com>]

> 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.


> 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