linux-ext4 - [PATCH 13/13] cifs: Fix race between hole punch and page fault

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Date:   Tue, 25 May 2021 15:50:50 +0200
From:   Jan Kara <jack@...e.cz>
To:     <linux-fsdevel@...r.kernel.org>
Cc:     Christoph Hellwig <hch@...radead.org>,
        Dave Chinner <david@...morbit.com>, ceph-devel@...r.kernel.org,
        Chao Yu <yuchao0@...wei.com>,
        Damien Le Moal <damien.lemoal@....com>,
        "Darrick J. Wong" <darrick.wong@...cle.com>,
        Jaegeuk Kim <jaegeuk@...nel.org>,
        Jeff Layton <jlayton@...nel.org>,
        Johannes Thumshirn <jth@...nel.org>,
        linux-cifs@...r.kernel.org, <linux-ext4@...r.kernel.org>,
        linux-f2fs-devel@...ts.sourceforge.net, <linux-mm@...ck.org>,
        <linux-xfs@...r.kernel.org>, Miklos Szeredi <miklos@...redi.hu>,
        Steve French <sfrench@...ba.org>, Ted Tso <tytso@....edu>,
        Matthew Wilcox <willy@...radead.org>, Jan Kara <jack@...e.cz>
Subject: [PATCH 13/13] cifs: Fix race between hole punch and page fault

Cifs has a following race between hole punching and page fault:

CPU1                                            CPU2
smb3_fallocate()
  smb3_punch_hole()
    truncate_pagecache_range()
                                                filemap_fault()
                                                  - loads old data into the
                                                    page cache
    SMB2_ioctl(..., FSCTL_SET_ZERO_DATA, ...)

And now we have stale data in the page cache. Fix the problem by locking
out faults (as well as reads) using mapping->invalidate_lock while hole
punch is running.

CC: Steve French <sfrench@...ba.org>
CC: linux-cifs@...r.kernel.org
Signed-off-by: Jan Kara <jack@...e.cz>
---
 fs/cifs/smb2ops.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/fs/cifs/smb2ops.c b/fs/cifs/smb2ops.c
index dd0eb665b680..b0a0f8b34add 100644
--- a/fs/cifs/smb2ops.c
+++ b/fs/cifs/smb2ops.c
@@ -3579,6 +3579,7 @@ static long smb3_punch_hole(struct file *file, struct cifs_tcon *tcon,
 		return rc;
 	}
 
+	down_write(&inode->i_mapping->invalidate_lock);
 	/*
 	 * We implement the punch hole through ioctl, so we need remove the page
 	 * caches first, otherwise the data may be inconsistent with the server.
@@ -3596,6 +3597,7 @@ static long smb3_punch_hole(struct file *file, struct cifs_tcon *tcon,
 			sizeof(struct file_zero_data_information),
 			CIFSMaxBufSize, NULL, NULL);
 	free_xid(xid);
+	up_write(&inode->i_mapping->invalidate_lock);
 	return rc;
 }
 
-- 
2.26.2