From: Cong Wang <[email protected]>
Date: Thu, 7 Jun 2018 13:39:49 -0700
> 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().
>
> sock_release() is called in many places, only the sock_close()
> path matters here. And fortunately, this should not affect normal
> sock_close() as it is only called when the last fd refcnt is gone.
> It only affects sock_close() with a parallel sockfs_setattr() in
> progress, which is not common.
>
> Fixes: 86741ec25462 ("net: core: Add a UID field to struct sock.")
> Reported-by: shankarapailoor <[email protected]>
> Cc: Tetsuo Handa <[email protected]>
> Cc: Lorenzo Colitti <[email protected]>
> Cc: Al Viro <[email protected]>
> Signed-off-by: Cong Wang <[email protected]>
I'm applying this for now, it is at least a step towards fixing
all of these issues.
If it is really offensive, I can revert, just tell me.
