Messages in this thread | | | From | "Eric W. Biederman" <> | Date | Tue, 08 Feb 2022 16:25:02 -0600 | Subject | Re: [PATCH] copy_process(): Move fd_install() out of sighand->siglock critical section |
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Al Viro <viro@zeniv.linux.org.uk> writes:
> On Tue, Feb 08, 2022 at 03:59:06PM -0600, Eric W. Biederman wrote: > >> The fd is being installed in the fdtable of the parent process, >> and the siglock and tasklist_lock are held to protect the child. >> >> >> Further fd_install is exposing the fd to userspace where it can be used >> by the process_madvise and the process_mrelease system calls, from >> anything that shares the fdtable of the parent thread. Which means it >> needs to be guaranteed that kernel_clone will call wake_up_process >> before it is safe to call fd_install. > > You mean "no calling fd_install() until after we are past the last possible > failure exit, by which point we know that wake_up_process() will eventually > be called", hopefully? If so (as I assumed all along), anything downstream > of > if (fatal_signal_pending(current)) { > retval = -EINTR; > goto bad_fork_cancel_cgroup; > } > > should be fine...
Except for the problems of calling fd_install under siglock, and tasklist_lock, which protect nothing and cause lockdep splats.
There may also be assumptions on the task actually being fully setup, if not today then in a future use pidfd. So I am not particularly comfortable with fd_install coming before we drop tasklist_lock.
I was pointing out that to resolve the locking issue we fundamentally can not move the fd_install earlier, to resolve the locking issues.
Eric
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