From 419e9c38aa075ed0cd3c13d47e15954b686bcdb6 Mon Sep 17 00:00:00 2001
From: Jan Kara <jack@suse.cz>
Date: Thu, 21 Nov 2019 16:14:38 -0800
Subject: [PATCH] iomap: Fix pipe page leakage during splicing
Git-commit: 419e9c38aa075ed0cd3c13d47e15954b686bcdb6
Patch-mainline: v5.5-rc1
References: bsc#1158651

When splicing using iomap_dio_rw() to a pipe, we may leak pipe pages
because bio_iov_iter_get_pages() records that the pipe will have full
extent worth of data however if file size is not block size aligned
iomap_dio_rw() returns less than what bio_iov_iter_get_pages() set up
and splice code gets confused leaking a pipe page with the file tail.

Handle the situation similarly to the old direct IO implementation and
revert iter to actually returned read amount which makes iter consistent
with value returned from iomap_dio_rw() and thus the splice code is
happy.

Fixes: ff6a9292e6f6 ("iomap: implement direct I/O")
Cc: stable@vger.kernel.org
Reported-by: syzbot+991400e8eba7e00a26e1@syzkaller.appspotmail.com
Signed-off-by: Jan Kara <jack@suse.cz>
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Acked-by: Jan Kara <jack@suse.cz>

---
 fs/iomap.c |    9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

--- a/fs/iomap.c
+++ b/fs/iomap.c
@@ -1046,8 +1046,15 @@ iomap_dio_rw(struct kiocb *iocb, struct
 		}
 		pos += ret;
 
-		if (iov_iter_rw(iter) == READ && pos >= dio->i_size)
+		if (iov_iter_rw(iter) == READ && pos >= dio->i_size) {
+			/*
+			 * We only report that we've read data up to i_size.
+			 * Revert iter to a state corresponding to that as
+			 * some callers (such as splice code) rely on it.
+			 */
+			iov_iter_revert(iter, pos - dio->i_size);
 			break;
+		}
 	} while ((count = iov_iter_count(iter)) > 0);
 	blk_finish_plug(&plug);