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nfsd: Lower NFSv4.1 callback message size limit

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The maximum size of a backchannel message on RPC-over-RDMA depends
on the connection's inline threshold. Today that threshold is
typically 1024 bytes, making the maximum message size 996 bytes.

The Linux server's CREATE_SESSION operation checks that the size
of callback Calls can be as large as 1044 bytes, to accommodate
RPCSEC_GSS. Thus CREATE_SESSION fails if a client advertises the
true message size maximum of 996 bytes.

But the server's backchannel currently does not support RPCSEC_GSS.
The actual maximum size it needs is much smaller. It is safe to
reduce the limit to enable NFSv4.1 on RDMA backchannel operation.

Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Signed-off-by: J. Bruce Fields <bfields@redhat.com>
This commit is contained in:
Chuck Lever 2016-03-01 13:06:02 -05:00 committed by J. Bruce Fields
parent f6763c29ab
commit 4500632f60
4 changed files with 24 additions and 14 deletions
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21
fs/nfsd/nfs4state.c
View File

@ -2587,21 +2587,26 @@ static __be32 check_forechannel_attrs(struct nfsd4_channel_attrs *ca, struct nfs
return nfs_ok;
}
/*
* Server's NFSv4.1 backchannel support is AUTH_SYS-only for now.
* These are based on similar macros in linux/sunrpc/msg_prot.h .
*/
#define RPC_MAX_HEADER_WITH_AUTH_SYS \
(RPC_CALLHDRSIZE + 2 * (2 + UNX_CALLSLACK))
#define RPC_MAX_REPHEADER_WITH_AUTH_SYS \
(RPC_REPHDRSIZE + (2 + NUL_REPLYSLACK))
#define NFSD_CB_MAX_REQ_SZ ((NFS4_enc_cb_recall_sz + \
RPC_MAX_HEADER_WITH_AUTH) * sizeof(__be32))
RPC_MAX_HEADER_WITH_AUTH_SYS) * sizeof(__be32))
#define NFSD_CB_MAX_RESP_SZ ((NFS4_dec_cb_recall_sz + \
RPC_MAX_REPHEADER_WITH_AUTH) * sizeof(__be32))
RPC_MAX_REPHEADER_WITH_AUTH_SYS) * \
sizeof(__be32))
static __be32 check_backchannel_attrs(struct nfsd4_channel_attrs *ca)
{
ca->headerpadsz = 0;
/*
* These RPC_MAX_HEADER macros are overkill, especially since we
* don't even do gss on the backchannel yet. But this is still
* less than 1k. Tighten up this estimate in the unlikely event
* it turns out to be a problem for some client:
*/
if (ca->maxreq_sz < NFSD_CB_MAX_REQ_SZ)
return nfserr_toosmall;
if (ca->maxresp_sz < NFSD_CB_MAX_RESP_SZ)

7
include/linux/sunrpc/auth.h
View File

@ -20,11 +20,18 @@
#include <linux/uidgid.h>
#include <linux/utsname.h>
/*
* Maximum size of AUTH_NONE authentication information, in XDR words.
*/
#define NUL_CALLSLACK (4)
#define NUL_REPLYSLACK (2)
/*
* Size of the nodename buffer. RFC1831 specifies a hard limit of 255 bytes,
* but Linux hostnames are actually limited to __NEW_UTS_LEN bytes.
*/
#define UNX_MAXNODENAME __NEW_UTS_LEN
#define UNX_CALLSLACK (21 + XDR_QUADLEN(UNX_MAXNODENAME))
struct rpcsec_gss_info;

4
net/sunrpc/auth_null.c
View File

@ -113,8 +113,8 @@ const struct rpc_authops authnull_ops = {
static
struct rpc_auth null_auth = {
.au_cslack = 4,
.au_rslack = 2,
.au_cslack = NUL_CALLSLACK,
.au_rslack = NUL_REPLYSLACK,
.au_ops = &authnull_ops,
.au_flavor = RPC_AUTH_NULL,
.au_count = ATOMIC_INIT(0),

6
net/sunrpc/auth_unix.c
View File

@ -23,8 +23,6 @@ struct unx_cred {
};
#define uc_uid uc_base.cr_uid
#define UNX_WRITESLACK (21 + XDR_QUADLEN(UNX_MAXNODENAME))
#if IS_ENABLED(CONFIG_SUNRPC_DEBUG)
# define RPCDBG_FACILITY RPCDBG_AUTH
#endif
@ -228,8 +226,8 @@ const struct rpc_authops authunix_ops = {
static
struct rpc_auth unix_auth = {
.au_cslack = UNX_WRITESLACK,
.au_rslack = 2, /* assume AUTH_NULL verf */
.au_cslack = UNX_CALLSLACK,
.au_rslack = NUL_REPLYSLACK,
.au_ops = &authunix_ops,
.au_flavor = RPC_AUTH_UNIX,
.au_count = ATOMIC_INIT(0),