Hi Olga,
On Wed, 2020-03-25 at 17:01 -0400, Olga Kornievskaia wrote:
> From: Olga Kornievskaia <kolga@xxxxxxxxxx>
>
> 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 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]
>
> 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@xxxxxxxxxx>
> ---
> 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)
>
> 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;
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():
auth->au_rslack = auth->au_verfsize + 2 +
XDR_QUADLEN(savedlen - rcv_buf->len);
auth->au_ralign = auth->au_verfsize + 2 +
XDR_QUADLEN(savedlen - rcv_buf->len);
My questions would be
- Are we sure that the above calculation (in gss_unwrap_resp_priv()) is
correct?
- Are we sure that the above calculation always gives the same answer
over time? We probably should not store a value that keeps changing.
--
Trond Myklebust
Linux NFS client maintainer, Hammerspace
trond.myklebust@xxxxxxxxxxxxxxx
