[PATCH] Split buffer overflow checking out of struct nfs4_compound

Here is the a pre-patch in the attempt to get rid of 'struct
nfs4_compound', and the associated horrible union in 'struct
nfs4_op'.

It splits out the fields that are meant to do buffer overflow checking
and iovec adjusting on the XDR received/sent data. It moves support
for that nto the dedicated structure 'xdr_stream', and the associated
functions 'xdr_reserve_space()', 'xdr_inline_decode()'.

The patch also expands out the all macros ENCODE_HEAD, ENCODE_TAIL,
ADJUST_ARGS and DECODE_HEAD, as well as most of the DECODE_TAILs.

1 files changed, 87 insertions, 0 deletions

diff --git a/include/linux/sunrpc/xdr.h b/include/linux/sunrpc/xdr.h
index 0233988f40b4..74c5260b2343 100644
--- a/include/linux/sunrpc/xdr.h
+++ b/include/linux/sunrpc/xdr.h
@@ -155,6 +155,93 @@ typedef size_t (*skb_read_actor_t)(skb_reader_t *desc, void *to, size_t len);
 extern void xdr_partial_copy_from_skb(struct xdr_buf *, unsigned int,
 		skb_reader_t *, skb_read_actor_t);
 
+/*
+ * Provide some simple tools for XDR buffer overflow-checking etc.
+ */
+struct xdr_stream {
+	uint32_t *p;		/* start of available buffer */
+	struct xdr_buf *buf;	/* XDR buffer to read/write */
+
+	uint32_t *end;		/* end of available buffer space */
+	struct iovec *iov;	/* pointer to the current iovec */
+};
+
+/*
+ * Initialize an xdr_stream for encoding data.
+ *
+ * Note: at the moment the RPC client only passes the length of our
+ *	 scratch buffer in the xdr_buf's header iovec. Previously this
+ *	 meant we needed to call xdr_adjust_iovec() after encoding the
+ *	 data. With the new scheme, the xdr_stream manages the details
+ *	 of the buffer length, and takes care of adjusting the iovec
+ *	 length for us.
+ */
+static inline void
+xdr_init_encode(struct xdr_stream *xdr, struct xdr_buf *buf, uint32_t *p)
+{
+	struct iovec *iov = buf->head;
+
+	xdr->buf = buf;
+	xdr->iov = iov;
+	xdr->end = (uint32_t *)((char *)iov->iov_base + iov->iov_len);
+	buf->len = iov->iov_len = (char *)p - (char *)iov->iov_base;
+	xdr->p = p;
+}
+
+/*
+ * Check that we have enough buffer space to encode 'nbytes' more
+ * bytes of data. If so, update the total xdr_buf length, and
+ * adjust the length of the current iovec.
+ */
+static inline uint32_t *
+xdr_reserve_space(struct xdr_stream *xdr, size_t nbytes)
+{
+	uint32_t *p = xdr->p;
+	uint32_t *q;
+
+	/* align nbytes on the next 32-bit boundary */
+	nbytes += 3;
+	nbytes &= ~3;
+	q = p + (nbytes >> 2);
+	if (unlikely(q > xdr->end || q < p))
+		return NULL;
+	xdr->p = q;
+	xdr->iov->iov_len += nbytes;
+	xdr->buf->len += nbytes;
+	return p;
+}
+
+/*
+ * Initialize an xdr_stream for decoding data.
+ */
+static inline void
+xdr_init_decode(struct xdr_stream *xdr, struct xdr_buf *buf, uint32_t *p)
+{
+	struct iovec *iov = buf->head;
+	xdr->buf = buf;
+	xdr->iov = iov;
+	xdr->p = p;
+	xdr->end = (uint32_t *)((char *)iov->iov_base + iov->iov_len);
+}
+
+/*
+ * Check if the input buffer is long enough to enable us to decode
+ * 'nbytes' more bytes of data starting at the current position.
+ * If so return the current pointer, then update the current
+ * position.
+ */
+static inline uint32_t *
+xdr_inline_decode(struct xdr_stream *xdr, size_t nbytes)
+{
+	uint32_t *p = xdr->p;
+	uint32_t *q = p + XDR_QUADLEN(nbytes);
+
+	if (unlikely(q > xdr->end || q < p))
+		return NULL;
+	xdr->p = q;
+	return p;
+}
+
 #endif /* __KERNEL__ */
 
 #endif /* _SUNRPC_XDR_H_ */