[PATCH 12/12] cifs: Fix race between hole punch and page fault

[Jan Kara <jack@suse.cz>]

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@samba.org>
CC: linux-cifs@vger.kernel.org
Signed-off-by: Jan Kara <jack@suse.cz>
---
 fs/cifs/smb2ops.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/fs/cifs/smb2ops.c b/fs/cifs/smb2ops.c
index f703204fb185..18231f9bc336 100644
--- a/fs/cifs/smb2ops.c
+++ b/fs/cifs/smb2ops.c
@@ -3543,6 +3543,7 @@ 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.
@@ -3560,6 +3561,7 @@ 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