Description of problem:

OpenSSH 7.6p1 sshd segfaults when closing SSH connection after which a coredump is generated by systemd. 

Version-Release number of selected component (if applicable):

Name         : openssh-server
Version      : 7.6p1
Release      : 2.fc27
Arch         : x86_64


How reproducible:

Update to openssh-server 7.6p1, establish a SSH connection to the machine using openssh, close the connection by issueing ctrl+d. 

Steps to Reproduce:
1. Establish a SSH connection to the machine using KiTTY 0.70.0.0 (Win10)
2. Close SSH connection by issueing ctrl+d
3. sshd segfaults, a core dump is generated.

Actual results:

Dec 11 02:42:52 oahu audit[1366]: ANOM_ABEND auid=0 uid=0 gid=0 ses=21 subj=unconfined_u:unconfined_r:unconfined_t:s0-s0:c0.c1023 pid=1366 comm="sshd" exe="/usr/sbin/sshd" sig=11 res=1
Dec 11 02:42:52 oahu kernel: sshd[1366]: segfault at 18 ip 0000564ac2e57c90 sp 00007ffe43b8c460 error 4 in sshd[564ac2e08000+c6000]
Dec 11 02:42:52 oahu systemd[1]: Started Process Core Dump (PID 1393/UID 0).
Dec 11 02:42:52 oahu systemd-coredump[1394]: Process 1366 (sshd) of user 0 dumped core.#012#012Stack trace of thread 1366:#012#0  0x0000564ac2e57c90 cipher_free (sshd)#012#1  0x0000564ac2e5be99 ssh_packet_close_internal (sshd)#012#2  0x0000564ac2e60c20 packet_close (sshd)#012#3  0x0000564ac2e1698e main (sshd)#012#4  0x00007f3931aac03a __libc_start_main (libc.so.6)#012#5  0x0000564ac2e17cfa _start (sshd)
Dec 11 02:42:52 oahu sshd[1355]: pam_unix(sshd:session): session closed for user fedorarules


Expected results:

Dec 11 02:43:40 palau sshd[2495]: pam_unix(sshd:session): session closed for user fedorarules


Additional info:

After downgrading to openssh-server 7.5p1 the problem is gone. This is the latest version of Kitty, the problem also happens with several tested older versions.