From db809e440eda6cc9a7e6633420668ea14c16ce6a Mon Sep 17 00:00:00 2001 From: Jeff Layton Date: Tue, 2 Sep 2008 19:25:05 +0000 Subject: cifs: fix O_APPEND on directio mounts commit 838726c4756813576078203eb7e1e219db0da870 upstream The direct I/O write codepath for CIFS is done through cifs_user_write(). That function does not currently call generic_write_checks() so the file position isn't being properly set when the file is opened with O_APPEND. It's also not doing the other "normal" checks that should be done for a write call. The problem is currently that when you open a file with O_APPEND on a mount with the directio mount option, the file position is set to the beginning of the file. This makes any subsequent writes clobber the data in the file starting at the beginning. This seems to fix the problem in cursory testing. It is, however important to note that NFS disallows the combination of (O_DIRECT|O_APPEND). If my understanding is correct, the concern is races with multiple clients appending to a file clobbering each others' data. Since the write model for CIFS and NFS is pretty similar in this regard, CIFS is probably subject to the same sort of races. What's unclear to me is why this is a particular problem with O_DIRECT and not with buffered writes... Regardless, disallowing O_APPEND on an entire mount is probably not reasonable, so we'll probably just have to deal with it and reevaluate this flag combination when we get proper support for O_DIRECT. In the meantime this patch at least fixes the existing problem. Signed-off-by: Jeff Layton Signed-off-by: Steve French Signed-off-by: Greg Kroah-Hartman --- fs/cifs/file.c | 4 ++++ 1 file changed, 4 insertions(+) diff --git a/fs/cifs/file.c b/fs/cifs/file.c index 0aac824371a..8da903b775b 100644 --- a/fs/cifs/file.c +++ b/fs/cifs/file.c @@ -832,6 +832,10 @@ ssize_t cifs_user_write(struct file *file, const char __user *write_data, return -EBADF; open_file = (struct cifsFileInfo *) file->private_data; + rc = generic_write_checks(file, poffset, &write_size, 0); + if (rc) + return rc; + xid = GetXid(); if (*poffset > file->f_path.dentry->d_inode->i_size) -- cgit v1.2.3-18-g5258