[PATCH 5.14 785/849] smb3: do not error on fsync when readonly

Greg Kroah-Hartman
2021-11-15T23:25:58Z

From: Steve French <stfrench@microsoft.com>

commit 71e6864eacbef0b2645ca043cdfbac272cb6cea3 upstream.

Linux allows doing a flush/fsync on a file open for read-only,
but the protocol does not allow that. If the file passed in
on the flush is read-only try to find a writeable handle for
the same inode, if that is not possible skip sending the
fsync call to the server to avoid breaking the apps.

Reported-by: Julian Sikorski <belegdol@gmail.com>
Tested-by: Julian Sikorski <belegdol@gmail.com>
Suggested-by: Jeremy Allison <jra@samba.org>
Reviewed-by: Paulo Alcantara (SUSE) <pc@cjr.nz>
Signed-off-by: Steve French <stfrench@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
fs/cifs/file.c | 35 +++++++++++++++++++++++++++++------
1 file changed, 29 insertions(+), 6 deletions(-)

--- a/fs/cifs/file.c
+++ b/fs/cifs/file.c
@@ -2689,12 +2689,23 @@ int cifs_strict_fsync(struct file *file,
tcon = tlink_tcon(smbfile->tlink);
if (!(cifs_sb->mnt_cifs_flags & CIFS_MOUNT_NOSSYNC)) {
server = tcon->ses->server;
- if (server->ops->flush)
- rc = server->ops->flush(xid, tcon, &smbfile->fid);
- else
+ if (server->ops->flush == NULL) {
rc = -ENOSYS;
+ goto strict_fsync_exit;
+ }
+
+ if ((OPEN_FMODE(smbfile->f_flags) & FMODE_WRITE) == 0) {
+ smbfile = find_writable_file(CIFS_I(inode), FIND_WR_ANY);
+ if (smbfile) {
+ rc = server->ops->flush(xid, tcon, &smbfile->fid);
+ cifsFileInfo_put(smbfile);
+ } else
+ cifs_dbg(FYI, "ignore fsync for file not open for write\n");
+ } else
+ rc = server->ops->flush(xid, tcon, &smbfile->fid);
}

+strict_fsync_exit:
free_xid(xid);
return rc;
}
@@ -2706,6 +2717,7 @@ int cifs_fsync(struct file *file, loff_t
struct cifs_tcon *tcon;
struct TCP_Server_Info *server;
struct cifsFileInfo *smbfile = file->private_data;
+ struct inode *inode = file_inode(file);
struct cifs_sb_info *cifs_sb = CIFS_FILE_SB(file);

rc = file_write_and_wait_range(file, start, end);
@@ -2722,12 +2734,23 @@ int cifs_fsync(struct file *file, loff_t
tcon = tlink_tcon(smbfile->tlink);
if (!(cifs_sb->mnt_cifs_flags & CIFS_MOUNT_NOSSYNC)) {
server = tcon->ses->server;
- if (server->ops->flush)
- rc = server->ops->flush(xid, tcon, &smbfile->fid);
- else
+ if (server->ops->flush == NULL) {
rc = -ENOSYS;
+ goto fsync_exit;
+ }
+
+ if ((OPEN_FMODE(smbfile->f_flags) & FMODE_WRITE) == 0) {
+ smbfile = find_writable_file(CIFS_I(inode), FIND_WR_ANY);
+ if (smbfile) {
+ rc = server->ops->flush(xid, tcon, &smbfile->fid);
+ cifsFileInfo_put(smbfile);
+ } else
+ cifs_dbg(FYI, "ignore fsync for file not open for write\n");
+ } else
+ rc = server->ops->flush(xid, tcon, &smbfile->fid);
}

+fsync_exit:
free_xid(xid);
return rc;
}