[PATCH 01/22] gss_krb5: introduce encryption type framework

steved
2010-03-15T13:26:23Z

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 | 14 ++++++--
net/sunrpc/auth_gss/gss_krb5_crypto.c | 56 +++++++++++++++++++++++++++++++++
net/sunrpc/auth_gss/gss_krb5_wrap.c | 7 ++--
net/sunrpc/auth_gss/gss_mech_switch.c | 14 ++++++++
net/sunrpc/auth_gss/svcauth_gss.c | 15 +++++++++
6 files changed, 123 insertions(+), 8 deletions(-)

diff --git a/include/linux/sunrpc/gss_krb5.h b/include/linux/sunrpc/gss_krb5.h
index e7bbdba..5bb227e 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_SLACK_CHECK \
+ BUILD_BUG_ON(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 > RPC_MAX_AUTH_SIZE)
+
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
+shift_head_data(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..a268368 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
@@ -1317,15 +1317,21 @@ gss_wrap_req_priv(struct rpc_cred *cred, struct gss_cl_ctx *ctx,
inpages = snd_buf->pages + first;
snd_buf->pages = rqstp->rq_enc_pages;
snd_buf->page_base -= first << PAGE_CACHE_SHIFT;
- /* Give the tail its own page, in case we need extra space in the
- * head when wrapping: */
+ /*
+ * Give the tail its own page, in case we need extra space in the
+ * head when wrapping:
+ *
+ * call_allocate() allocates twice the slack space required
+ * by the authentication flavor to rq_callsize.
+ * For GSS, slack is GSS_CRED_SLACK.
+ */
if (snd_buf->page_len || snd_buf->tail[0].iov_len) {
tmp = page_address(rqstp->rq_enc_pages[rqstp->rq_enc_pages_num - 1]);
memcpy(tmp, snd_buf->tail[0].iov_base, snd_buf->tail[0].iov_len);
snd_buf->tail[0].iov_base = tmp;
}
maj_stat = gss_wrap(ctx->gc_gss_ctx, offset, snd_buf, inpages);
- /* RPC_SLACK_SPACE should prevent this ever happening: */
+ /* slack space should prevent this ever happening: */
BUG_ON(snd_buf->len > snd_buf->buflen);
status = -EIO;
/* We're assuming that when GSS_S_CONTEXT_EXPIRED, the encryption was
diff --git a/net/sunrpc/auth_gss/gss_krb5_crypto.c b/net/sunrpc/auth_gss/gss_krb5_crypto.c
index c93fca2..d0f3371 100644
--- a/net/sunrpc/auth_gss/gss_krb5_crypto.c
+++ b/net/sunrpc/auth_gss/gss_krb5_crypto.c
@@ -326,3 +326,59 @@ 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
+shift_head_data(struct xdr_buf *buf, unsigned int base, unsigned int shiftlen)
+{
+ u8 *p;
+
+ if (shiftlen == 0)
+ return 0;
+
+ GSS_KRB5_SLACK_CHECK;
+ BUG_ON(shiftlen > RPC_MAX_AUTH_SIZE);
+
+ /*
+ * If there is a tail, and it shares a page with the head,
+ * make sure we don't clobber the tail. This is a just a
+ * defensive check.
+ */
+ if (buf->tail[0].iov_base != NULL) {
+ if ((((long)buf->tail[0].iov_base >> PAGE_CACHE_SHIFT) ==
+ ((long)buf->head[0].iov_base >> PAGE_CACHE_SHIFT)) &&
+ buf->tail[0].iov_base - buf->head[0].iov_base < shiftlen) {
+ dprintk("%s: collision: head %p:%zu, tail %p:%zu, "
+ "shiftlen %u\n",
+ __func__, buf->head[0].iov_base,
+ buf->head[0].iov_len, buf->tail[0].iov_base,
+ buf->tail[0].iov_len, shiftlen);
+ return 1;
+ }
+ }
+
+ 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..a0660f5 100644
--- a/net/sunrpc/auth_gss/gss_krb5_wrap.c
+++ b/net/sunrpc/auth_gss/gss_krb5_wrap.c
@@ -144,6 +144,7 @@ gss_wrap_kerberos(struct gss_ctx *ctx, int offset,

dprintk("RPC: gss_wrap_kerberos\n");

+ GSS_KRB5_SLACK_CHECK;
now = get_seconds();

blocksize = crypto_blkcipher_blocksize(kctx->enc);
@@ -156,11 +157,9 @@ gss_wrap_kerberos(struct gss_ctx *ctx, int offset,

ptr = buf->head[0].iov_base + offset;
/* shift data to make room for header. */
+ shift_head_data(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,
diff --git a/net/sunrpc/auth_gss/gss_mech_switch.c b/net/sunrpc/auth_gss/gss_mech_switch.c
index 76e4c6f..28a84ef 100644
--- a/net/sunrpc/auth_gss/gss_mech_switch.c
+++ b/net/sunrpc/auth_gss/gss_mech_switch.c
@@ -285,6 +285,20 @@ gss_verify_mic(struct gss_ctx *context_handle,
mic_token);
}

+/*
+ * This function is called from both the client and server code.
+ * Each makes guarantees about how much "slack" space is available
+ * for the underlying function in "buf"'s head and tail while
+ * performing the wrap.
+ *
+ * The client and server code allocate RPC_MAX_AUTH_SIZE extra
+ * space in both the head and tail which is available for use by
+ * the wrap function.
+ *
+ * Underlying functions should verify they do not use more than
+ * RPC_MAX_AUTH_SIZE of extra space in either the head or tail
+ * when performing the wrap.
+ */
u32
gss_wrap(struct gss_ctx *ctx_id,
int offset,
diff --git a/net/sunrpc/auth_gss/svcauth_gss.c b/net/sunrpc/auth_gss/svcauth_gss.c
index e34bc53..4eec8ba 100644
--- a/net/sunrpc/auth_gss/svcauth_gss.c
+++ b/net/sunrpc/auth_gss/svcauth_gss.c
@@ -1314,6 +1314,14 @@ svcauth_gss_wrap_resp_priv(struct svc_rqst *rqstp)
inpages = resbuf->pages;
/* XXX: Would be better to write some xdr helper functions for
* nfs{2,3,4}xdr.c that place the data right, instead of copying: */
+
+ /*
+ * If there is currently tail data, make sure there is
+ * room for the head, tail, and 2 * RPC_MAX_AUTH_SIZE in
+ * the page, and move the current tail data such that
+ * there is RPC_MAX_AUTH_SIZE slack space available in
+ * both the head and tail.
+ */
if (resbuf->tail[0].iov_base) {
BUG_ON(resbuf->tail[0].iov_base >= resbuf->head[0].iov_base
+ PAGE_SIZE);
@@ -1326,6 +1334,13 @@ svcauth_gss_wrap_resp_priv(struct svc_rqst *rqstp)
resbuf->tail[0].iov_len);
resbuf->tail[0].iov_base += RPC_MAX_AUTH_SIZE;
}
+ /*
+ * If there is no current tail data, make sure there is
+ * room for the head data, and 2 * RPC_MAX_AUTH_SIZE in the
+ * allotted page, and set up tail information such that there
+ * is RPC_MAX_AUTH_SIZE slack space available in both the
+ * head and tail.
+ */
if (resbuf->tail[0].iov_base == NULL) {
if (resbuf->head[0].iov_len + 2*RPC_MAX_AUTH_SIZE > PAGE_SIZE)
return -ENOMEM;
--
1.6.6.1