Re: [PATCH 2/3] net/scm: cleanup scm_detach_fds

Ido Schimmel
2020-05-13T09:58:24Z

On Wed, May 13, 2020 at 11:49:08AM +0200, Christoph Hellwig wrote:
> On Wed, May 13, 2020 at 12:29:18PM +0300, Ido Schimmel wrote:
> > On Mon, May 11, 2020 at 01:59:12PM +0200, Christoph Hellwig wrote:
> > > Factor out two helpes to keep the code tidy.
> > >
> > > Signed-off-by: Christoph Hellwig <hch@lst.de>
> >
> > Christoph,
> >
> > After installing net-next (fb9f2e92864f) on a Fedora 32 machine I cannot
> > ssh to it. Bisected it to this commit [1].
> >
> > When trying to connect I see these error messages in journal:
> >
> > sshd[1029]: error: mm_receive_fd: no message header
> > sshd[1029]: fatal: mm_pty_allocate: receive fds failed
> > sshd[1029]: fatal: mm_request_receive_expect: buffer error: incomplete message
> > sshd[1018]: fatal: mm_request_receive: read: Connection reset by peer
> >
> > Please let me know if more info is required. I can easily test a patch
> > if you need me to try something.
>
> To start we can try reverting just this commit, which requires a
> little manual work. Patch below:

Thanks for the quick reply. With the below patch ssh is working again.

>
> ---
> From fe4f53219b42aeded3c1464dbe2bbc9365f6a853 Mon Sep 17 00:00:00 2001
> From: Christoph Hellwig <hch@lst.de>
> Date: Wed, 13 May 2020 11:48:33 +0200
> Subject: Revert "net/scm: cleanup scm_detach_fds"
>
> This reverts commit 2618d530dd8b7ac0fdcb83f4c95b88f7b0d37ce6.
> ---
> net/core/scm.c | 94 +++++++++++++++++++++++---------------------------
> 1 file changed, 43 insertions(+), 51 deletions(-)
>
> diff --git a/net/core/scm.c b/net/core/scm.c
> index a75cd637a71ff..2d9aa5682bed2 100644
> --- a/net/core/scm.c
> +++ b/net/core/scm.c
> @@ -280,53 +280,18 @@ void put_cmsg_scm_timestamping(struct msghdr *msg, struct scm_timestamping_inter
> }
> EXPORT_SYMBOL(put_cmsg_scm_timestamping);
>
> -static int __scm_install_fd(struct file *file, int __user *ufd, int o_flags)
> -{
> - struct socket *sock;
> - int new_fd;
> - int error;
> -
> - error = security_file_receive(file);
> - if (error)
> - return error;
> -
> - new_fd = get_unused_fd_flags(o_flags);
> - if (new_fd < 0)
> - return new_fd;
> -
> - error = put_user(new_fd, ufd);
> - if (error) {
> - put_unused_fd(new_fd);
> - return error;
> - }
> -
> - /* Bump the usage count and install the file. */
> - sock = sock_from_file(file, &error);
> - if (sock) {
> - sock_update_netprioidx(&sock->sk->sk_cgrp_data);
> - sock_update_classid(&sock->sk->sk_cgrp_data);
> - }
> - fd_install(new_fd, get_file(file));
> - return error;
> -}
> -
> -static int scm_max_fds(struct msghdr *msg)
> -{
> - if (msg->msg_controllen <= sizeof(struct cmsghdr))
> - return 0;
> - return (msg->msg_controllen - sizeof(struct cmsghdr)) / sizeof(int);
> -}
> -
> void scm_detach_fds(struct msghdr *msg, struct scm_cookie *scm)
> {
> struct cmsghdr __user *cm
> = (__force struct cmsghdr __user*)msg->msg_control;
> - int o_flags = (msg->msg_flags & MSG_CMSG_CLOEXEC) ? O_CLOEXEC : 0;
> - int fdmax = min_t(int, scm_max_fds(msg), scm->fp->count);
> - int __user *cmsg_data = CMSG_USER_DATA(cm);
> +
> + int fdmax = 0;
> + int fdnum = scm->fp->count;
> + struct file **fp = scm->fp->fp;
> + int __user *cmfptr;
> int err = 0, i;
>
> - if (msg->msg_flags & MSG_CMSG_COMPAT) {
> + if (MSG_CMSG_COMPAT & msg->msg_flags) {
> scm_detach_fds_compat(msg, scm);
> return;
> }
> @@ -335,35 +300,62 @@ void scm_detach_fds(struct msghdr *msg, struct scm_cookie *scm)
> if (WARN_ON_ONCE(!msg->msg_control_is_user))
> return;
>
> - for (i = 0; i < fdmax; i++) {
> - err = __scm_install_fd(scm->fp->fp[i], cmsg_data + i, o_flags);
> + if (msg->msg_controllen > sizeof(struct cmsghdr))
> + fdmax = ((msg->msg_controllen - sizeof(struct cmsghdr))
> + / sizeof(int));
> +
> + if (fdnum < fdmax)
> + fdmax = fdnum;
> +
> + for (i=0, cmfptr =(int __user *)CMSG_USER_DATA(cm); i<fdmax;
> + i++, cmfptr++)
> + {
> + struct socket *sock;
> + int new_fd;
> + err = security_file_receive(fp[i]);
> if (err)
> break;
> + err = get_unused_fd_flags(MSG_CMSG_CLOEXEC & msg->msg_flags
> + ? O_CLOEXEC : 0);
> + if (err < 0)
> + break;
> + new_fd = err;
> + err = put_user(new_fd, cmfptr);
> + if (err) {
> + put_unused_fd(new_fd);
> + break;
> + }
> + /* Bump the usage count and install the file. */
> + sock = sock_from_file(fp[i], &err);
> + if (sock) {
> + sock_update_netprioidx(&sock->sk->sk_cgrp_data);
> + sock_update_classid(&sock->sk->sk_cgrp_data);
> + }
> + fd_install(new_fd, get_file(fp[i]));
> }
>
> - if (i > 0) {
> - int cmlen = CMSG_LEN(i * sizeof(int));
> -
> + if (i > 0)
> + {
> + int cmlen = CMSG_LEN(i*sizeof(int));
> err = put_user(SOL_SOCKET, &cm->cmsg_level);
> if (!err)
> err = put_user(SCM_RIGHTS, &cm->cmsg_type);
> if (!err)
> err = put_user(cmlen, &cm->cmsg_len);
> if (!err) {
> - cmlen = CMSG_SPACE(i * sizeof(int));
> + cmlen = CMSG_SPACE(i*sizeof(int));
> if (msg->msg_controllen < cmlen)
> cmlen = msg->msg_controllen;
> msg->msg_control += cmlen;
> msg->msg_controllen -= cmlen;
> }
> }
> -
> - if (i < scm->fp->count || (scm->fp->count && fdmax <= 0))
> + if (i < fdnum || (fdnum && fdmax <= 0))
> msg->msg_flags |= MSG_CTRUNC;
>
> /*
> - * All of the files that fit in the message have had their usage counts
> - * incremented, so we just free the list.
> + * All of the files that fit in the message have had their
> + * usage counts incremented, so we just free the list.
> */
> __scm_destroy(scm);
> }
> --
> 2.26.2
>