libceph: account for alignment in pages cursor

When a cursor for a page array data message is initialized it needs
to determine the initial value for cursor->last_piece.  Currently it
just checks if length is less than a page, but that's not correct.
The data in the first page in the array will be offset by a page
offset based on the alignment recorded for the data.  (All pages
thereafter will be aligned at the base of the page, so there's
no need to account for this except for the first page.)

Because this was wrong, there was a case where the length of a piece
would be calculated as all of the residual bytes in the message and
that plus the page offset could exceed the length of a page.

So fix this case.  Make sure the sum won't wrap.

This resolves a third issue described in:
    http://tracker.ceph.com/issues/4598

Signed-off-by: Alex Elder <elder@inktank.com>
Reviewed-by: Sage Weil <sage@inktank.com>

diff --git a/net/ceph/messenger.c b/net/ceph/messenger.c
index 198b9026288e54d5a06c74978c2856c6b1c5af1b..ee160864e8eabcbcea9d1f32e14bc9de01f763d7 100644 (file)
--- a/net/ceph/messenger.c
+++ b/net/ceph/messenger.c
@@ -839,9 +839,10 @@ static void ceph_msg_data_pages_cursor_init(struct ceph_msg_data *data,
        page_count = calc_pages_for(data->alignment, (u64)data->length);
        cursor->page_offset = data->alignment & ~PAGE_MASK;
        cursor->page_index = 0;
-       BUG_ON(page_count > (int) USHRT_MAX);
-       cursor->page_count = (unsigned short) page_count;
-       cursor->last_piece = length <= PAGE_SIZE;
+       BUG_ON(page_count > (int)USHRT_MAX);
+       cursor->page_count = (unsigned short)page_count;
+       BUG_ON(length > SIZE_MAX - cursor->page_offset);
+       cursor->last_piece = (size_t)cursor->page_offset + length <= PAGE_SIZE;
 }
 
 static struct page *ceph_msg_data_pages_next(struct ceph_msg_data *data,