From: Miklos Szeredi <mszeredi@redhat.com>
Date: Thu, 18 Aug 2016 07:10:44 +0000 (+0200)
Subject: fuse: fix fuse_write_end() if zero bytes were copied
X-Git-Tag: v5.15~12469^2
X-Git-Url: http://review.tizen.org/git/?a=commitdiff_plain;h=59c3b76cc61d1d676f965c192cc7969aa5cb2744;p=platform%2Fkernel%2Flinux-starfive.git

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>
---

diff --git a/fs/fuse/file.c b/fs/fuse/file.c
index abc66a6..2401c5d 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);