lkml.org 
[lkml]   [2020]   [May]   [29]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH v2 2/3] seccomp: Introduce addfd ioctl to seccomp user notifier
> 
> I mean, yes, that's certainly better, but it just seems a shame that
> everyone has to do the get_unused/put_unused dance just because of how
> SCM_RIGHTS does this weird put_user() in the middle.
>
> Can anyone clarify the expected failure mode from SCM_RIGHTS? Can we
> move the put_user() after instead? I think cleanup would just be:
> replace_fd(fd, NULL, 0)
>
> So:
>
> (updated to skip sock updates on failure; thank you Christian!)
>
> int file_receive(int fd, unsigned long flags, struct file *file)
> {
> struct socket *sock;
> int ret;
>
> ret = security_file_receive(file);
> if (ret)
> return ret;
>
> /* Install the file. */
> if (fd == -1) {
> ret = get_unused_fd_flags(flags);
> if (ret >= 0)
> fd_install(ret, get_file(file));
> } else {
> ret = replace_fd(fd, file, flags);
> }
>
> /* Bump the sock usage counts. */
> if (ret >= 0) {
> sock = sock_from_file(addfd->file, &err);
> if (sock) {
> sock_update_netprioidx(&sock->sk->sk_cgrp_data);
> sock_update_classid(&sock->sk->sk_cgrp_data);
> }
> }
>
> return ret;
> }
>
> scm_detach_fds()
> ...
> for (i=0, cmfptr=(__force int __user *)CMSG_DATA(cm); i<fdmax;
> i++, cmfptr++)
> {
> int new_fd;
>
> err = file_receive(-1, MSG_CMSG_CLOEXEC & msg->msg_flags
> ? O_CLOEXEC : 0, fp[i]);
> if (err < 0)
> break;
> new_fd = err;
>
Isn't the "right" way to do this to allocate a bunch of file descriptors,
and fill up the user buffer with them, and then install the files? This
seems to like half-install the file descriptors and then error out.

I know that's the current behaviour, but that seems like a bad idea. Do
we really want to perpetuate this half-broken state? I guess that some
userspace programs could be depending on this -- and their recovery
semantics could rely on this. I mean this is 10+ year old code.

> err = put_user(err, cmfptr);
> if (err) {
> /*
> * If we can't notify userspace that it got the
> * fd, we need to unwind and remove it again.
> */
> replace_fd(new_fd, NULL, 0);
> break;
> }
> }
> ...
>
>
>
> --
> Kees Cook

\
 
 \ /
  Last update: 2020-05-30 05:59    [W:0.097 / U:3.384 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site