fuse: fix fuse_write_end() if zero bytes were copied

If pos is at the beginning of a page and copied is zero then page is not
zeroed but is marked uptodate.

Fix by skipping everything except unlock/put of page if zero bytes were
copied.

Reported-by: Al Viro <viro@zeniv.linux.org.uk>
Fixes: 6b12c1b37e55 ("fuse: Implement write_begin/write_end callbacks")
Cc: <stable@vger.kernel.org> # v3.15+
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>

1 files changed, 6 insertions, 0 deletions

diff --git a/fs/fuse/file.c b/fs/fuse/file.c
index abc66a6237fd..2401c5dabb2a 100644
--- a/fs/fuse/file.c
+++ b/fs/fuse/file.c
@@ -1985,6 +1985,10 @@ static int fuse_write_end(struct file *file, struct address_space *mapping,
 {
         struct inode *inode = page->mapping->host;
 
+        /* Haven't copied anything?  Skip zeroing, size extending, dirtying. */
+        if (!copied)
+                goto unlock;
+
         if (!PageUptodate(page)) {
                 /* Zero any unwritten bytes at the end of the page */
                 size_t endoff = (pos + copied) & ~PAGE_MASK;
@@ -1995,6 +1999,8 @@ static int fuse_write_end(struct file *file, struct address_space *mapping,
 
         fuse_write_update_size(inode, pos + copied);
         set_page_dirty(page);
+
+unlock:
         unlock_page(page);
         put_page(page);