rpc: define xdr_restrict_buflen

With this xdr_reserve_space can help us enforce various limits.

Signed-off-by: J. Bruce Fields <bfields@redhat.com>

2 files changed, 30 insertions, 0 deletions

diff --git a/include/linux/sunrpc/xdr.h b/include/linux/sunrpc/xdr.h
index b23d69ffd5ec..70c6b92e15a7 100644
--- a/include/linux/sunrpc/xdr.h
+++ b/include/linux/sunrpc/xdr.h
@@ -217,6 +217,7 @@ extern void xdr_init_encode(struct xdr_stream *xdr, struct xdr_buf *buf, __be32
 extern __be32 *xdr_reserve_space(struct xdr_stream *xdr, size_t nbytes);
 extern void xdr_commit_encode(struct xdr_stream *xdr);
 extern void xdr_truncate_encode(struct xdr_stream *xdr, size_t len);
+extern int xdr_restrict_buflen(struct xdr_stream *xdr, int newbuflen);
 extern void xdr_write_pages(struct xdr_stream *xdr, struct page **pages,
                 unsigned int base, unsigned int len);
 extern unsigned int xdr_stream_pos(const struct xdr_stream *xdr);
diff --git a/net/sunrpc/xdr.c b/net/sunrpc/xdr.c
index 2b546e8ce43d..39928444c7fb 100644
--- a/net/sunrpc/xdr.c
+++ b/net/sunrpc/xdr.c
@@ -649,6 +649,35 @@ void xdr_truncate_encode(struct xdr_stream *xdr, size_t len)
 EXPORT_SYMBOL(xdr_truncate_encode);
 
 /**
+ * xdr_restrict_buflen - decrease available buffer space
+ * @xdr: pointer to xdr_stream
+ * @newbuflen: new maximum number of bytes available
+ *
+ * Adjust our idea of how much space is available in the buffer.
+ * If we've already used too much space in the buffer, returns -1.
+ * If the available space is already smaller than newbuflen, returns 0
+ * and does nothing.  Otherwise, adjusts xdr->buf->buflen to newbuflen
+ * and ensures xdr->end is set at most offset newbuflen from the start
+ * of the buffer.
+ */
+int xdr_restrict_buflen(struct xdr_stream *xdr, int newbuflen)
+{
+        struct xdr_buf *buf = xdr->buf;
+        int left_in_this_buf = (void *)xdr->end - (void *)xdr->p;
+        int end_offset = buf->len + left_in_this_buf;
+
+        if (newbuflen < 0 || newbuflen < buf->len)
+                return -1;
+        if (newbuflen > buf->buflen)
+                return 0;
+        if (newbuflen < end_offset)
+                xdr->end = (void *)xdr->end + newbuflen - end_offset;
+        buf->buflen = newbuflen;
+        return 0;
+}
+EXPORT_SYMBOL(xdr_restrict_buflen);
+
+/**
  * xdr_write_pages - Insert a list of pages into an XDR buffer for sending
  * @xdr: pointer to xdr_stream
  * @pages: list of pages