[PATCH] netfs: Miscellaneous fixes

[David Howells]

Fix some miscellaneous things in the new netfs lib[1]:

 (1) The kerneldoc for netfs_readpage() shouldn't say netfs_page().

 (2) netfs_readpage() can get an integer overflow on 32-bit when it
     multiplies page_index(page) by PAGE_SIZE.  It should use
     page_offset() instead.

 (3) netfs_write_begin() should also use page_offset() to avoid the same
     overflow.

 (4) Use page_mapping() in netfs_write_begin() rather than page->mapping.

Reported-by: Matthew Wilcox <willy at infradead.org>
Signed-off-by: David Howells <dhowells at redhat.com>
Link: https://lore.kernel.org/r/161789062190.6155.12711584466338493050.stgit@warthog.procyon.org.uk/ [1]
---
 fs/netfs/read_helper.c |    8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/fs/netfs/read_helper.c b/fs/netfs/read_helper.c
index 1d3b50c5db6d..568e26352309 100644
--- a/fs/netfs/read_helper.c
+++ b/fs/netfs/read_helper.c
@@ -933,7 +933,7 @@ void netfs_readahead(struct readahead_control *ractl,
 EXPORT_SYMBOL(netfs_readahead);
 
 /**
- * netfs_page - Helper to manage a readpage request
+ * netfs_readpage - Helper to manage a readpage request
  * @file: The file to read from
  * @page: The page to read
  * @ops: The network filesystem's operations for the helper to use
@@ -968,7 +968,7 @@ int netfs_readpage(struct file *file,
 		return -ENOMEM;
 	}
 	rreq->mapping	= page_file_mapping(page);
-	rreq->start	= page_index(page) * PAGE_SIZE;
+	rreq->start	= page_offset(page);
 	rreq->len	= thp_size(page);
 
 	if (ops->begin_cache_operation) {
@@ -1105,8 +1105,8 @@ int netfs_write_begin(struct file *file, struct address_space *mapping,
 	rreq = netfs_alloc_read_request(ops, netfs_priv, file);
 	if (!rreq)
 		goto error;
-	rreq->mapping		= page->mapping;
-	rreq->start		= page->index * PAGE_SIZE;
+	rreq->mapping		= page_file_mapping(page);
+	rreq->start		= page_offset(page);
 	rreq->len		= thp_size(page);
 	rreq->no_unlock_page	= page->index;
 	__set_bit(NETFS_RREQ_NO_UNLOCK_PAGE, &rreq->flags);