[PATCH v6 2/4] iomap: Fix use-after-free error in page_done callback

[Andreas Gruenbacher <agruenba@redhat.com>]

In iomap_write_end, we're not holding a page reference anymore when
calling the page_done callback, but the callback needs that reference to
access the page.  To fix that, move the put_page call in
__generic_write_end into the callers of __generic_write_end.  Then, in
iomap_write_end, put the page after calling the page_done callback.

Reported-by: Jan Kara <jack@suse.cz>
Fixes: 63899c6f8851 ("iomap: add a page_done callback")
Signed-off-by: Andreas Gruenbacher <agruenba@redhat.com>
Reviewed-by: Jan Kara <jack@suse.cz>
---
 fs/buffer.c | 5 +++--
 fs/iomap.c  | 1 +
 2 files changed, 4 insertions(+), 2 deletions(-)

diff --git a/fs/buffer.c b/fs/buffer.c
index ce357602f471..6e2c95160ce3 100644
--- a/fs/buffer.c
+++ b/fs/buffer.c
@@ -2104,7 +2104,6 @@ int __generic_write_end(struct inode *inode, loff_t pos, unsigned copied,
 	}
 
 	unlock_page(page);
-	put_page(page);
 
 	if (old_size < pos)
 		pagecache_isize_extended(inode, old_size, pos);
@@ -2160,7 +2159,9 @@ int generic_write_end(struct file *file, struct address_space *mapping,
 			struct page *page, void *fsdata)
 {
 	copied = block_write_end(file, mapping, pos, len, copied, page, fsdata);
-	return __generic_write_end(mapping->host, pos, copied, page);
+	copied = __generic_write_end(mapping->host, pos, copied, page);
+	put_page(page);
+	return copied;
 }
 EXPORT_SYMBOL(generic_write_end);
 
diff --git a/fs/iomap.c b/fs/iomap.c
index 2344c662e6fc..b01ed5a28d2c 100644
--- a/fs/iomap.c
+++ b/fs/iomap.c
@@ -780,6 +780,7 @@ iomap_write_end(struct inode *inode, loff_t pos, unsigned len,
 	ret = __generic_write_end(inode, pos, ret, page);
 	if (iomap->page_done)
 		iomap->page_done(inode, pos, copied, page, iomap);
+	put_page(page);
 
 	if (ret < len)
 		iomap_write_failed(inode, pos, len);
-- 
2.20.1