[PATCH 10/18] SUNRPC: Switch MIC token verification to crypto/krb5

[Chuck Lever <cel@kernel.org>]

From: Chuck Lever <chuck.lever@oracle.com>

gss_krb5_verify_mic_v2() currently recomputes a checksum using
gss_krb5_checksum() and then compares it against the received
checksum with memcmp(). Replace this with a call to
crypto_krb5_verify_mic(), which performs the hash, comparison,
and offset/length adjustment in a single operation through the
crypto/krb5 library.

The scatterlist layout required by RFC 4121 Section 4.2.4 is
constructed via gss_krb5_mic_build_sg(), the shared helper
introduced in the preceding commit. The received checksum
occupies the first scatterlist entry, pointing directly into
the token buffer.

The errno result from crypto_krb5_verify_mic() is mapped to a
GSS major status code via gss_krb5_errno_to_status(), which
returns GSS_S_BAD_SIG for -EBADMSG (checksum mismatch).

Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
---
 net/sunrpc/auth_gss/gss_krb5_unseal.c | 36 ++++++++++++++++++++++-------------
 1 file changed, 23 insertions(+), 13 deletions(-)

diff --git a/net/sunrpc/auth_gss/gss_krb5_unseal.c b/net/sunrpc/auth_gss/gss_krb5_unseal.c
index ef0e6af9fc95..b5fb70419faa 100644
--- a/net/sunrpc/auth_gss/gss_krb5_unseal.c
+++ b/net/sunrpc/auth_gss/gss_krb5_unseal.c
@@ -60,6 +60,8 @@
 #include <linux/types.h>
 #include <linux/jiffies.h>
 #include <linux/sunrpc/gss_krb5.h>
+#include <linux/scatterlist.h>
+#include <linux/slab.h>
 
 #include "gss_krb5_internal.h"
 
@@ -71,18 +73,19 @@ u32
 gss_krb5_verify_mic_v2(struct krb5_ctx *ctx, struct xdr_buf *message_buffer,
 		       struct xdr_netobj *read_token)
 {
-	struct crypto_ahash *tfm = ctx->initiate ?
-				   ctx->acceptor_sign : ctx->initiator_sign;
-	char cksumdata[GSS_KRB5_MAX_CKSUM_LEN];
-	struct xdr_netobj cksumobj = {
-		.len	= ctx->gk5e->cksumlength,
-		.data	= cksumdata,
-	};
+	const struct krb5_enctype *krb5 = ctx->krb5e;
+	struct crypto_shash *shash = ctx->initiate ?
+		ctx->acceptor_sign_shash : ctx->initiator_sign_shash;
+	unsigned int cksum_len = krb5->cksum_len;
+	struct scatterlist sg_head[XDR_BUF_TO_SG_NENTS];
+	struct scatterlist *sg_overflow;
+	size_t mic_offset, mic_len;
 	u8 *ptr = read_token->data;
 	__be16 be16_ptr;
 	time64_t now;
 	u8 flags;
-	int i;
+	int nsg, i;
+	int ret;
 
 	dprintk("RPC:       %s\n", __func__);
 
@@ -104,13 +107,20 @@ gss_krb5_verify_mic_v2(struct krb5_ctx *ctx, struct xdr_buf *message_buffer,
 		if (ptr[i] != 0xff)
 			return GSS_S_DEFECTIVE_TOKEN;
 
-	if (gss_krb5_checksum(tfm, ptr, GSS_KRB5_TOK_HDR_LEN,
-			      message_buffer, 0, &cksumobj))
+	nsg = gss_krb5_mic_build_sg(message_buffer,
+				    ptr + GSS_KRB5_TOK_HDR_LEN,
+				    cksum_len, ptr,
+				    sg_head, &sg_overflow);
+	if (nsg < 0)
 		return GSS_S_FAILURE;
 
-	if (memcmp(cksumobj.data, ptr + GSS_KRB5_TOK_HDR_LEN,
-				ctx->gk5e->cksumlength))
-		return GSS_S_BAD_SIG;
+	mic_offset = 0;
+	mic_len = cksum_len + message_buffer->len + GSS_KRB5_TOK_HDR_LEN;
+	ret = crypto_krb5_verify_mic(krb5, shash, NULL, sg_head, nsg,
+				     &mic_offset, &mic_len);
+	kfree(sg_overflow);
+	if (ret)
+		return gss_krb5_errno_to_status(ret);
 
 	/* it got through unscathed.  Make sure the context is unexpired */
 	now = ktime_get_real_seconds();

-- 
2.53.0