[PATCH 11/11] cifs: Fix race between hole punch and page fault

Jan Kara
2021-05-12T13:46:55Z

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 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