From 838726c4756813576078203eb7e1e219db0da870 Mon Sep 17 00:00:00 2001 From: Jeff Layton Date: Thu, 28 Aug 2008 07:54:59 -0400 Subject: [PATCH] cifs: fix O_APPEND on directio mounts 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 Cc: Stable Tree Signed-off-by: Steve French --- fs/cifs/file.c | 4 ++++ 1 file changed, 4 insertions(+) diff --git a/fs/cifs/file.c b/fs/cifs/file.c index ff14d14903..cbefe1f1f9 100644 --- a/fs/cifs/file.c +++ b/fs/cifs/file.c @@ -833,6 +833,10 @@ 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) -- 2.39.5