On Wed, Jan 27, 2021 at 12:21 PM Stefan Hajnoczi <stefa...@redhat.com> wrote:
}
> @@ -1654,9 +1677,11 @@ static void update_open_flags(int writeback, int
> allow_direct_io,
> static void lo_create(fuse_req_t req, fuse_ino_t parent, const char *name,
> mode_t mode, struct fuse_file_info *fi)
> {
> + int open_flags = (fi->flags | O_CREAT) & ~O_NOFOLLOW;
> int fd;
> struct lo_data *lo = lo_data(req);
> struct lo_inode *parent_inode;
> + struct lo_inode *existing_inode = NULL;
> struct fuse_entry_param e;
> int err;
> struct lo_cred old = {};
> @@ -1682,11 +1707,23 @@ static void lo_create(fuse_req_t req, fuse_ino_t
> parent, const char *name,
>
> update_open_flags(lo->writeback, lo->allow_direct_io, fi);
>
> - fd = openat(parent_inode->fd, name, (fi->flags | O_CREAT) & ~O_NOFOLLOW,
> - mode);
> + /* First, try to create a new file but don't open existing files */
> + fd = openat(parent_inode->fd, name, open_flags | O_EXCL, mode);
> err = fd == -1 ? errno : 0;
> +
> lo_restore_cred(&old);
>
> + /* Second, open existing files if O_EXCL was not specified */
> + if (err == EEXIST && !(fi->flags & O_EXCL)) {
> + existing_inode = lookup_name(req, parent, name);
> + if (existing_inode) {
> + fd = lo_inode_open(lo, existing_inode, open_flags);
> + if (fd < 0) {
> + err = -fd;
> + }
> + }
> + }
> +
> if (!err) {
> ssize_t fh;
It's more of a mess than I thought.
The problem here is there can also be a race between the open and the
subsequent lo_do_lookup().
At this point it's probably enough to verify that fuse_entry_param
refers to the same object as the fh (using fstat and comparing st_dev
and st_ino).
Also O_CREAT open is not supposed to return ENOENT, so failure to open
without O_CREAT (race between O_CREAT open and plain open) should at
least translate error to ESTALE or EIO.
Thanks,
Miklos
