From: Chuck Lever <chuck.lever@xxxxxxxxxx>
Other common Kerberos implementations use a fully random confounder
for encryption. For a Kerberos implementation that is part of an O/S
I/O stack, this is impractical. However, using a fast PRG that does
not deplete the system entropy pool is possible and desirable.
Use an atomic type to ensure that confounder generation
deterministically generates a unique and pseudo-random result in the
face of concurrent execution, and make the confounder generation
materials unique to each Keberos context. The latter has several
benefits:
- the internal counter will wrap less often
- no way to guess confounders based on other Kerberos-encrypted
traffic
- better scalability
Since confounder generation is part of Kerberos itself rather than
the GSS-API Kerberos mechanism, the function is renamed and moved.
Tested-by: Scott Mayhew <smayhew@xxxxxxxxxx>
Signed-off-by: Chuck Lever <chuck.lever@xxxxxxxxxx>
---
include/linux/sunrpc/gss_krb5.h | 7 +++---
net/sunrpc/auth_gss/gss_krb5_crypto.c | 28 ++++++++++++++++++++++-
net/sunrpc/auth_gss/gss_krb5_internal.h | 13 +++++++++++
net/sunrpc/auth_gss/gss_krb5_mech.c | 17 +++++++-------
net/sunrpc/auth_gss/gss_krb5_wrap.c | 38 ++-----------------------------
5 files changed, 56 insertions(+), 47 deletions(-)
create mode 100644 net/sunrpc/auth_gss/gss_krb5_internal.h
diff --git a/include/linux/sunrpc/gss_krb5.h b/include/linux/sunrpc/gss_krb5.h
index 51860e3a0216..192f5b37763f 100644
--- a/include/linux/sunrpc/gss_krb5.h
+++ b/include/linux/sunrpc/gss_krb5.h
@@ -38,6 +38,8 @@
#define _LINUX_SUNRPC_GSS_KRB5_H
#include <crypto/skcipher.h>
+#include <linux/siphash.h>
+
#include <linux/sunrpc/auth_gss.h>
#include <linux/sunrpc/gss_err.h>
#include <linux/sunrpc/gss_asn1.h>
@@ -106,6 +108,8 @@ struct krb5_ctx {
atomic_t seq_send;
atomic64_t seq_send64;
time64_t endtime;
+ atomic64_t confounder;
+ siphash_key_t confkey;
struct xdr_netobj mech_used;
u8 initiator_sign[GSS_KRB5_MAX_KEYLEN];
u8 acceptor_sign[GSS_KRB5_MAX_KEYLEN];
@@ -311,7 +315,4 @@ gss_krb5_aes_decrypt(struct krb5_ctx *kctx, u32 offset, u32 len,
struct xdr_buf *buf, u32 *plainoffset,
u32 *plainlen);
-void
-gss_krb5_make_confounder(char *p, u32 conflen);
-
#endif /* _LINUX_SUNRPC_GSS_KRB5_H */
diff --git a/net/sunrpc/auth_gss/gss_krb5_crypto.c b/net/sunrpc/auth_gss/gss_krb5_crypto.c
index 8aa5610ef660..6d962079aa95 100644
--- a/net/sunrpc/auth_gss/gss_krb5_crypto.c
+++ b/net/sunrpc/auth_gss/gss_krb5_crypto.c
@@ -47,10 +47,36 @@
#include <linux/sunrpc/gss_krb5.h>
#include <linux/sunrpc/xdr.h>
+#include "gss_krb5_internal.h"
+
#if IS_ENABLED(CONFIG_SUNRPC_DEBUG)
# define RPCDBG_FACILITY RPCDBG_AUTH
#endif
+/**
+ * krb5_make_confounder - Generate a unique pseudorandom string
+ * @kctx: Kerberos context
+ * @p: memory location into which to write the string
+ * @conflen: string length to write, in octets
+ *
+ * To avoid draining the system's entropy pool when under heavy
+ * encrypted I/O loads, the @kctx has a small amount of random seed
+ * data that is then hashed to generate each pseudorandom confounder
+ * string.
+ */
+void
+krb5_make_confounder(struct krb5_ctx *kctx, u8 *p, int conflen)
+{
+ u64 *q = (u64 *)p;
+
+ WARN_ON_ONCE(conflen < sizeof(*q));
+ while (conflen > 0) {
+ *q++ = siphash_1u64(atomic64_inc_return(&kctx->confounder),
+ &kctx->confkey);
+ conflen -= sizeof(*q);
+ }
+}
+
u32
krb5_encrypt(
struct crypto_sync_skcipher *tfm,
@@ -630,7 +656,7 @@ gss_krb5_aes_encrypt(struct krb5_ctx *kctx, u32 offset,
offset += GSS_KRB5_TOK_HDR_LEN;
if (xdr_extend_head(buf, offset, conflen))
return GSS_S_FAILURE;
- gss_krb5_make_confounder(buf->head[0].iov_base + offset, conflen);
+ krb5_make_confounder(kctx, buf->head[0].iov_base + offset, conflen);
offset -= GSS_KRB5_TOK_HDR_LEN;
if (buf->tail[0].iov_base != NULL) {
diff --git a/net/sunrpc/auth_gss/gss_krb5_internal.h b/net/sunrpc/auth_gss/gss_krb5_internal.h
new file mode 100644
index 000000000000..6249124aba1d
--- /dev/null
+++ b/net/sunrpc/auth_gss/gss_krb5_internal.h
@@ -0,0 +1,13 @@
+/* SPDX-License-Identifier: GPL-2.0 or BSD-3-Clause */
+/*
+ * SunRPC GSS Kerberos 5 mechanism internal definitions
+ *
+ * Copyright (c) 2022 Oracle and/or its affiliates.
+ */
+
+#ifndef _NET_SUNRPC_AUTH_GSS_KRB5_INTERNAL_H
+#define _NET_SUNRPC_AUTH_GSS_KRB5_INTERNAL_H
+
+void krb5_make_confounder(struct krb5_ctx *kctx, u8 *p, int conflen);
+
+#endif /* _NET_SUNRPC_AUTH_GSS_KRB5_INTERNAL_H */
diff --git a/net/sunrpc/auth_gss/gss_krb5_mech.c b/net/sunrpc/auth_gss/gss_krb5_mech.c
index 08a86ece665e..6d59794c9b69 100644
--- a/net/sunrpc/auth_gss/gss_krb5_mech.c
+++ b/net/sunrpc/auth_gss/gss_krb5_mech.c
@@ -550,16 +550,17 @@ gss_import_sec_context_kerberos(const void *p, size_t len,
ret = gss_import_v1_context(p, end, ctx);
else
ret = gss_import_v2_context(p, end, ctx, gfp_mask);
-
- if (ret == 0) {
- ctx_id->internal_ctx_id = ctx;
- if (endtime)
- *endtime = ctx->endtime;
- } else
+ if (ret) {
kfree(ctx);
+ return ret;
+ }
- dprintk("RPC: %s: returning %d\n", __func__, ret);
- return ret;
+ ctx_id->internal_ctx_id = ctx;
+ if (endtime)
+ *endtime = ctx->endtime;
+ atomic64_set(&ctx->confounder, get_random_u64());
+ get_random_bytes(&ctx->confkey, sizeof(ctx->confkey));
+ return 0;
}
static void
diff --git a/net/sunrpc/auth_gss/gss_krb5_wrap.c b/net/sunrpc/auth_gss/gss_krb5_wrap.c
index bd068e936947..374214f3c463 100644
--- a/net/sunrpc/auth_gss/gss_krb5_wrap.c
+++ b/net/sunrpc/auth_gss/gss_krb5_wrap.c
@@ -32,9 +32,10 @@
#include <linux/types.h>
#include <linux/jiffies.h>
#include <linux/sunrpc/gss_krb5.h>
-#include <linux/random.h>
#include <linux/pagemap.h>
+#include "gss_krb5_internal.h"
+
#if IS_ENABLED(CONFIG_SUNRPC_DEBUG)
# define RPCDBG_FACILITY RPCDBG_AUTH
#endif
@@ -113,39 +114,6 @@ gss_krb5_remove_padding(struct xdr_buf *buf, int blocksize)
return 0;
}
-void
-gss_krb5_make_confounder(char *p, u32 conflen)
-{
- static u64 i = 0;
- u64 *q = (u64 *)p;
-
- /* rfc1964 claims this should be "random". But all that's really
- * necessary is that it be unique. And not even that is necessary in
- * our case since our "gssapi" implementation exists only to support
- * rpcsec_gss, so we know that the only buffers we will ever encrypt
- * already begin with a unique sequence number. Just to hedge my bets
- * I'll make a half-hearted attempt at something unique, but ensuring
- * uniqueness would mean worrying about atomicity and rollover, and I
- * don't care enough. */
-
- /* initialize to random value */
- if (i == 0) {
- i = get_random_u32();
- i = (i << 32) | get_random_u32();
- }
-
- switch (conflen) {
- case 16:
- *q++ = i++;
- fallthrough;
- case 8:
- *q++ = i++;
- break;
- default:
- BUG();
- }
-}
-
/* Assumptions: the head and tail of inbuf are ours to play with.
* The pages, however, may be real pages in the page cache and we replace
* them with scratch pages from **pages before writing to them. */
@@ -211,7 +179,7 @@ gss_wrap_kerberos_v1(struct krb5_ctx *kctx, int offset,
ptr[6] = 0xff;
ptr[7] = 0xff;
- gss_krb5_make_confounder(msg_start, conflen);
+ krb5_make_confounder(kctx, msg_start, conflen);
if (kctx->gk5e->keyed_cksum)
cksumkey = kctx->cksum;
