SUNRPC: Convert svcauth_unix_accept() to use xdr_stream

Done as part of hardening the server-side RPC header decoding path.

Since the server-side of the Linux kernel SunRPC implementation
ignores the contents of the Call's machinename field, there's no
need for its RPC_AUTH_UNIX authenticator to reject names that are
larger than UNX_MAXNODENAME.
Reviewed-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>

include/linux/sunrpc/msg_prot.h

@@ -34,6 +34,11 @@ enum rpc_auth_flavors {
 	RPC_AUTH_GSS_SPKMP = 390011,
 };
 
+/* Maximum size (in octets) of the machinename in an AUTH_UNIX
+ * credential (per RFC 5531 Appendix A)
+ */
+#define RPC_MAX_MACHINENAME	(255)
+
 /* Maximum size (in bytes) of an rpc credential or verifier */
 #define RPC_MAX_AUTH_SIZE (400)
 

net/sunrpc/svcauth_unix.c

@@ -867,26 +867,45 @@ struct auth_ops svcauth_tls = {
 };
 
 
+/**
+ * svcauth_unix_accept - Decode and validate incoming RPC_AUTH_SYS credential
+ * @rqstp: RPC transaction
+ *
+ * Return values:
+ *   %SVC_OK: Both credential and verifier are valid
+ *   %SVC_DENIED: Credential or verifier is not valid
+ *   %SVC_GARBAGE: Failed to decode credential or verifier
+ *   %SVC_CLOSE: Temporary failure
+ *
+ * rqstp->rq_auth_stat is set as mandated by RFC 5531.
+ */
 static int
 svcauth_unix_accept(struct svc_rqst *rqstp)
 {
-	struct kvec	*argv = &rqstp->rq_arg.head[0];
 	struct kvec	*resv = &rqstp->rq_res.head[0];
+	struct xdr_stream *xdr = &rqstp->rq_arg_stream;
 	struct svc_cred	*cred = &rqstp->rq_cred;
 	struct user_namespace *userns;
-	u32		slen, i;
-	int		len   = argv->iov_len;
+	u32 flavor, len, i;
+	void *body;
+	__be32 *p;
+
+	svcxdr_init_decode(rqstp);
 
-	if ((len -= 3*4) < 0)
+	/*
+	 * This implementation ignores the length of the Call's
+	 * credential body field and the timestamp and machinename
+	 * fields.
+	 */
+	p = xdr_inline_decode(xdr, XDR_UNIT * 3);
+	if (!p)
+		return SVC_GARBAGE;
+	len = be32_to_cpup(p + 2);
+	if (len > RPC_MAX_MACHINENAME)
+		return SVC_GARBAGE;
+	if (!xdr_inline_decode(xdr, len))
 		return SVC_GARBAGE;
 
-	svc_getu32(argv);			/* length */
-	svc_getu32(argv);			/* time stamp */
-	slen = XDR_QUADLEN(svc_getnl(argv));	/* machname length */
-	if (slen > 64 || (len -= (slen + 3)*4) < 0)
-		goto badcred;
-	argv->iov_base = (void*)((__be32*)argv->iov_base + slen);	/* skip machname */
-	argv->iov_len -= slen*4;
 	/*
 	 * Note: we skip uid_valid()/gid_valid() checks here for
 	 * backwards compatibility with clients that use -1 id's.
@@ -896,20 +915,33 @@ svcauth_unix_accept(struct svc_rqst *rqstp)
 	 */
 	userns = (rqstp->rq_xprt && rqstp->rq_xprt->xpt_cred) ?
 		rqstp->rq_xprt->xpt_cred->user_ns : &init_user_ns;
-	cred->cr_uid = make_kuid(userns, svc_getnl(argv)); /* uid */
-	cred->cr_gid = make_kgid(userns, svc_getnl(argv)); /* gid */
-	slen = svc_getnl(argv);			/* gids length */
-	if (slen > UNX_NGROUPS || (len -= (slen + 2)*4) < 0)
+	if (xdr_stream_decode_u32(xdr, &i) < 0)
+		return SVC_GARBAGE;
+	cred->cr_uid = make_kuid(userns, i);
+	if (xdr_stream_decode_u32(xdr, &i) < 0)
+		return SVC_GARBAGE;
+	cred->cr_gid = make_kgid(userns, i);
+
+	if (xdr_stream_decode_u32(xdr, &len) < 0)
+		return SVC_GARBAGE;
+	if (len > UNX_NGROUPS)
 		goto badcred;
-	cred->cr_group_info = groups_alloc(slen);
+	p = xdr_inline_decode(xdr, XDR_UNIT * len);
+	if (!p)
+		return SVC_GARBAGE;
+	cred->cr_group_info = groups_alloc(len);
 	if (cred->cr_group_info == NULL)
 		return SVC_CLOSE;
-	for (i = 0; i < slen; i++) {
-		kgid_t kgid = make_kgid(userns, svc_getnl(argv));
+	for (i = 0; i < len; i++) {
+		kgid_t kgid = make_kgid(userns, be32_to_cpup(p++));
 		cred->cr_group_info->gid[i] = kgid;
 	}
 	groups_sort(cred->cr_group_info);
-	if (svc_getu32(argv) != htonl(RPC_AUTH_NULL) || svc_getu32(argv) != 0) {
+
+	/* Call's verf field: */
+	if (xdr_stream_decode_opaque_auth(xdr, &flavor, &body, &len) < 0)
+		return SVC_GARBAGE;
+	if (flavor != RPC_AUTH_NULL || len != 0) {
 		rqstp->rq_auth_stat = rpc_autherr_badverf;
 		return SVC_DENIED;
 	}
@@ -919,7 +951,6 @@ svcauth_unix_accept(struct svc_rqst *rqstp)
 	svc_putnl(resv, 0);
 
 	rqstp->rq_cred.cr_flavor = RPC_AUTH_UNIX;
-	svcxdr_init_decode(rqstp);
 	return SVC_OK;
 
 badcred: