[Bug 2864] New: ssh client 7.7p1: "Tunnel device open failed." (regression from 7.6p1)

[bugzilla-daemon at bugzilla.mindrot.org]

https://bugzilla.mindrot.org/show_bug.cgi?id=2864

            Bug ID: 2864
           Summary: ssh client 7.7p1: "Tunnel device open failed."
                    (regression from 7.6p1)
           Product: Portable OpenSSH
           Version: 7.7p1
          Hardware: amd64
                OS: Linux
            Status: NEW
          Severity: major
          Priority: P5
         Component: ssh
          Assignee: unassigned-bugs at mindrot.org
          Reporter: calimeroteknik at free.fr

Created attachment 3148
  --> https://bugzilla.mindrot.org/attachment.cgi?id=3148&action=edit
ssh -vvv -w0:0 remotehost for 7.6p1 and 7.7p1

I have tun0 set up on the local and remote host.

Here is what happens with 7.7p1:

calimero at localhost ~ $ ssh -w0:0 remotehost
Tunnel device open failed.
Could not request tunnel forwarding.
calimero at remotehost ~ $

For the verbose (-vvv) output, which didn't seem extremely helpful, see
attachment.


Here are strace excerpts:


For 7.6p1:

openat(AT_FDCWD, "/dev/net/tun", O_RDWR) = 4
ioctl(4, TUNSETIFF, 0x7fffaeea8490)     = 0
fcntl(4, F_SETFD, FD_CLOEXEC)           = 0
fcntl(4, F_GETFL)                       = 0x8002 (flags
O_RDWR|O_LARGEFILE)
fcntl(4, F_SETFL, O_RDWR|O_NONBLOCK|O_LARGEFILE) = 0
fcntl(4, F_GETFL)                       = 0x8802 (flags
O_RDWR|O_NONBLOCK|O_LARGEFILE)
getpid()                                = 4905
dup(0)                                  = 5
dup(1)                                  = 6
dup(2)                                  = 7


For 7.7p1:

openat(AT_FDCWD, "/dev/net/tun", O_RDWR) = 4
ioctl(4, TUNSETIFF, 0x7ffcb8813710)     = 0
close(4)                                = 0
write(2, "Tunnel device open failed.\r\n", 28Tunnel device open failed.
) = 28
write(2, "Could not request tunnel forward"..., 38Could not request
tunnel forwarding.
) = 38
dup(0)                                  = 4
dup(1)                                  = 5
dup(2)                                  = 6

Reproducible at will on this box running arch linux with kernel 4.16.6
(same bug also experienced on 4.16.4).
Upgrading or downgrading openssh takes seconds.

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