untrusted comment: signature from openbsd 6.1 base secret key
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OpenBSD 6.1 errata 021, August 3, 2017:

An uninitialized variable in ptrace() may result in an info leak.

Apply by doing:
   signify -Vep /etc/signify/openbsd-61-base.pub -x 021_ptrace.patch.sig \
       -m - | (cd /usr/src && patch -p0)

And then rebuild and install a new kernel:
   KK=`sysctl -n kern.osversion | cut -d# -f1`
   cd /usr/src/sys/arch/`machine`/compile/$KK
   make obj
   make config
   make
   make install

Index: sys/kern/sys_process.c
===================================================================
RCS file: /cvs/src/sys/kern/sys_process.c,v
--- sys/kern/sys_process.c      25 Jan 2017 07:35:04 -0000      1.76
+++ sys/kern/sys_process.c      19 Jul 2017 14:17:49 -0000      1.77
@@ -101,7 +101,7 @@ sys_ptrace(struct proc *p, void *v, regi
       register_t wcookie;
#endif
       int error, write;
-       int temp;
+       int temp = 0;
       int req = SCARG(uap, req);
       pid_t pid = SCARG(uap, pid);
       caddr_t addr = SCARG(uap, addr);