vfs: fix uninitialized flags in splice_to_pipe()

commit 5a81e6a1 upstream.

Flags (PIPE_BUF_FLAG_PACKET, PIPE_BUF_FLAG_GIFT) could remain on the
unused part of the pipe ring buffer.  Previously splice_to_pipe() left
the flags value alone, which could result in incorrect behavior.

Uninitialized flags appears to have been there from the introduction of
the splice syscall.
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
[bwh: Backported to 3.16: adjust context, indentation]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

fs/splice.c

@@ -212,6 +212,7 @@ ssize_t splice_to_pipe(struct pipe_inode_info *pipe,
 			buf->len = spd->partial[page_nr].len;
 			buf->private = spd->partial[page_nr].private;
 			buf->ops = spd->ops;
+			buf->flags = 0;
 			if (spd->flags & SPLICE_F_GIFT)
 				buf->flags |= PIPE_BUF_FLAG_GIFT;