On Thu, Jun 07, 2018 at 02:45:58PM -0700, Cong Wang wrote: > On Thu, Jun 7, 2018 at 2:26 PM, Al Viro <v...@zeniv.linux.org.uk> wrote: > > On Thu, Jun 07, 2018 at 01:39:49PM -0700, Cong Wang wrote: > >> fchownat() doesn't even hold refcnt of fd until it figures out > >> fd is really needed (otherwise is ignored) and releases it after > >> it resolves the path. This means sock_close() could race with > >> sockfs_setattr(), which leads to a NULL pointer dereference > >> since typically we set sock->sk to NULL in ->release(). > >> > >> As pointed out by Al, this is unique to sockfs. So we can fix this > >> in socket layer by acquiring inode_lock in sock_close() and > >> checking against NULL in sockfs_setattr(). > > > > That looks like a massive overkill - it's way heavier than it should be. > > I don't see any other quick way to fix this. My initial thought is > to keep that refcnt until path_put(), apparently you don't like it > either.
You do realize that the same ->setattr() can be called by way of chown() on /proc/self/fd/<n>, right? What would you do there - bump refcount on that struct file when traversing that symlink and hold it past the end of pathname resolution, until... what exactly?
