On Wed, Mar 25, 2020 at 5:55 PM Chuck Lever <chuck.lever@xxxxxxxxxx> wrote:
>
>
>
> > On Mar 25, 2020, at 5:52 PM, Trond Myklebust <trondmy@xxxxxxxxxxxxxxx> wrote:
> >
> > On Wed, 2020-03-25 at 17:43 -0400, Chuck Lever wrote:
> >>> On Mar 25, 2020, at 5:33 PM, Trond Myklebust <
> >>> trondmy@xxxxxxxxxxxxxxx> wrote:
> >>>
> >>> 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 refe
> >>>> ren
> >>>> 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);
> >>
> >> 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
> >>>
> >>> - 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.
> >>
> >
> > OK. So you're both saying that as long as the initial value is correct,
> > we're good for the duration of the GSS session? Fair enough, I'll apply
> > this patch for 5.7 then.
>
> Thanks, please see my one-line correction. I think the definition of
> GSS_RESP_SLACK should not include the "<< 2", I would like Olga to
> confirm.
Yes I do.
> > Let's also fix up the above in a separate patch to not keep setting
> > auth->au_rslack / auth->au_ralign if their values are not changing.
> > That should prevent unnecessary cache line bouncing.
>
> I volunteer, unless Olga wants to take it.
Please do the fix (as because I'm not understanding what needs to be
fixed and I'd be bugging you folks to explain it first).
>
>
> --
> Chuck Lever
>
>
>
