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

Christoph Hellwig
2020-05-13T10:03:17Z

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:

---
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