[PATCH 01/23] gss_krb5: Introduce encryption type framework

steved
2010-03-17T17:03:11Z

Make the client and server code consistent regarding the extra buffer
space made available for the auth code when wrapping data.

Add some comments/documentation about the available buffer space
in the xdr_buf head and tail when gss_wrap is called.

Add a compile-time check to make sure we are not exceeding the available
buffer space.

Add a central function to shift head data.

Signed-off-by: Kevin Coffman <kwc@citi.umich.edu>
Signed-off-by: Steve Dickson <steved@redhat.com>
---
include/linux/sunrpc/gss_krb5.h | 25 +++++++++++++++++++++
net/sunrpc/auth_gss/auth_gss.c | 2 +-
net/sunrpc/auth_gss/gss_krb5_crypto.c | 38 +++++++++++++++++++++++++++++++++
net/sunrpc/auth_gss/gss_krb5_wrap.c | 6 +---
4 files changed, 66 insertions(+), 5 deletions(-)

diff --git a/include/linux/sunrpc/gss_krb5.h b/include/linux/sunrpc/gss_krb5.h
index e7bbdba..00dc5cf 100644
--- a/include/linux/sunrpc/gss_krb5.h
+++ b/include/linux/sunrpc/gss_krb5.h
@@ -40,6 +40,12 @@
#include <linux/sunrpc/gss_err.h>
#include <linux/sunrpc/gss_asn1.h>

+/* Maximum checksum function output for the supported crypto algorithms */
+#define GSS_KRB5_MAX_CKSUM_LEN (20)
+
+/* Maximum blocksize for the supported crypto algorithms */
+#define GSS_KRB5_MAX_BLOCKSIZE (16)
+
struct krb5_ctx {
int initiate; /* 1 = initiating, 0 = accepting */
struct crypto_blkcipher *enc;
@@ -113,6 +119,22 @@ enum seal_alg {
#define ENCTYPE_DES3_CBC_SHA1 0x0010
#define ENCTYPE_UNKNOWN 0x01ff

+/*
+ * This compile-time check verifies that we will not exceed the
+ * slack space allotted by the client and server auth_gss code
+ * before they call gss_wrap().
+ */
+#define GSS_KRB5_MAX_SLACK_NEEDED \
+ GSS_KRB5_TOK_HDR_LEN /* gss token header */ \
+ + GSS_KRB5_MAX_CKSUM_LEN /* gss token checksum */ \
+ + GSS_KRB5_MAX_BLOCKSIZE /* confounder */ \
+ + GSS_KRB5_MAX_BLOCKSIZE /* possible padding */ \
+ + GSS_KRB5_TOK_HDR_LEN /* encrypted hdr in v2 token */\
+ + GSS_KRB5_MAX_CKSUM_LEN /* encryption hmac */ \
+ + 4 + 4 /* RPC verifier */ \
+ + GSS_KRB5_TOK_HDR_LEN \
+ + GSS_KRB5_MAX_CKSUM_LEN
+
s32
make_checksum(char *, char *header, int hdrlen, struct xdr_buf *body,
int body_offset, struct xdr_netobj *cksum);
@@ -157,3 +179,6 @@ s32
krb5_get_seq_num(struct crypto_blkcipher *key,
unsigned char *cksum,
unsigned char *buf, int *direction, u32 *seqnum);
+
+int
+xdr_extend_head(struct xdr_buf *buf, unsigned int base, unsigned int shiftlen);
diff --git a/net/sunrpc/auth_gss/auth_gss.c b/net/sunrpc/auth_gss/auth_gss.c
index 0cfccc2..7c50ea6 100644
--- a/net/sunrpc/auth_gss/auth_gss.c
+++ b/net/sunrpc/auth_gss/auth_gss.c
@@ -61,7 +61,7 @@ static const struct rpc_credops gss_nullops;
# define RPCDBG_FACILITY RPCDBG_AUTH
#endif

-#define GSS_CRED_SLACK 1024
+#define GSS_CRED_SLACK (RPC_MAX_AUTH_SIZE * 2)
/* length of a krb5 verifier (48), plus data added before arguments when
* using integrity (two 4-byte integers): */
#define GSS_VERF_SLACK 100
diff --git a/net/sunrpc/auth_gss/gss_krb5_crypto.c b/net/sunrpc/auth_gss/gss_krb5_crypto.c
index c93fca2..52dfde0 100644
--- a/net/sunrpc/auth_gss/gss_krb5_crypto.c
+++ b/net/sunrpc/auth_gss/gss_krb5_crypto.c
@@ -326,3 +326,41 @@ gss_decrypt_xdr_buf(struct crypto_blkcipher *tfm, struct xdr_buf *buf,

return xdr_process_buf(buf, offset, buf->len - offset, decryptor, &desc);
}
+
+/*
+ * This function makes the assumption that it was ultimately called
+ * from gss_wrap().
+ *
+ * The client auth_gss code moves any existing tail data into a
+ * separate page before calling gss_wrap.
+ * The server svcauth_gss code ensures that both the head and the
+ * tail have slack space of RPC_MAX_AUTH_SIZE before calling gss_wrap.
+ *
+ * Even with that guarantee, this function may be called more than
+ * once in the processing of gss_wrap(). The best we can do is
+ * verify at compile-time (see GSS_KRB5_SLACK_CHECK) that the
+ * largest expected shift will fit within RPC_MAX_AUTH_SIZE.
+ * At run-time we can verify that a single invocation of this
+ * function doesn't attempt to use more the RPC_MAX_AUTH_SIZE.
+ */
+
+int
+xdr_extend_head(struct xdr_buf *buf, unsigned int base, unsigned int shiftlen)
+{
+ u8 *p;
+
+ if (shiftlen == 0)
+ return 0;
+
+ BUILD_BUG_ON(GSS_KRB5_MAX_SLACK_NEEDED > RPC_MAX_AUTH_SIZE);
+ BUG_ON(shiftlen > RPC_MAX_AUTH_SIZE);
+
+ p = buf->head[0].iov_base + base;
+
+ memmove(p + shiftlen, p, buf->head[0].iov_len - base);
+
+ buf->head[0].iov_len += shiftlen;
+ buf->len += shiftlen;
+
+ return 0;
+}
diff --git a/net/sunrpc/auth_gss/gss_krb5_wrap.c b/net/sunrpc/auth_gss/gss_krb5_wrap.c
index ae8e69b..8bc3701 100644
--- a/net/sunrpc/auth_gss/gss_krb5_wrap.c
+++ b/net/sunrpc/auth_gss/gss_krb5_wrap.c
@@ -156,11 +156,9 @@ gss_wrap_kerberos(struct gss_ctx *ctx, int offset,

ptr = buf->head[0].iov_base + offset;
/* shift data to make room for header. */
+ xdr_extend_head(buf, offset, headlen);
+
/* XXX Would be cleverer to encrypt while copying. */
- /* XXX bounds checking, slack, etc. */
- memmove(ptr + headlen, ptr, buf->head[0].iov_len - offset);
- buf->head[0].iov_len += headlen;
- buf->len += headlen;
BUG_ON((buf->len - offset - headlen) % blocksize);

g_make_token_header(&kctx->mech_used,
--
1.6.6.1